Updated on 2022/12/27

写真a

 
TAKENAKA Hiroshi
 
Organization
Faculty of Natural Science and Technology Professor
Position
Professor
External link

Degree

  • Master of Science ( Hokkaido University )

  • Doctor of Science ( Hokkaido University )

Research Interests

  • 地震防災

  • 波動計算

  • スタガード格子

  • 弾性波動

  • 地質波形

  • 地震波動シミュレーション

  • シミュレーション

  • 計算法

  • Q

  • 強震動

  • 地震波動

  • 1次元構造

  • イメージング

  • 火山体

  • 海溝型地震

  • 弾性波

  • 弾性波動論

  • 地球内部構造

  • 人工地震探査

  • 人工地震質探査

  • 自然災害

  • 減衰

  • 差分法

  • 地震

  • 平面波

  • 数値シミュレーション

  • 2.5次元

  • 理論地震記象

  • 粘弾性体

  • 地震波形

  • 固体地球物理学

  • 地球物理学

  • Strong motion

  • 地震工学

  • 震源過程

  • 地震学

  • 地震波

  • Seismology

  • Seismic wave

  • Earthquake engineering

Research Areas

  • Natural Science / Solid earth sciences

  • Social Infrastructure (Civil Engineering, Architecture, Disaster Prevention) / Disaster prevention engineering

  • Natural Science / Solid earth sciences

  • Social Infrastructure (Civil Engineering, Architecture, Disaster Prevention) / Disaster prevention engineering

Research History

  • Okayama University   学術研究院自然科学学域   Professor

    2021.4

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    Country:Japan

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  • Okayama University   大学院・自然科学研究科   Professor

    2013.5 - 2020.3

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Professional Memberships

  • 日本地震学会

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  • 日本火山学会

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  • 米国地震学会(Seismological Society of America)

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  • 米国応用数理学会(Society for Industrial and Applied Mathematics)

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  • 米国音響学会(Acoustical Society of American)

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  • 米国物理探査学会(Society of Exploration Geophysicists)

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  • 日本応用数理学会

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  • 物理探査学会

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  • 米国地球物理学連合(American Geophysical Union)

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  • 英国王立天文学会(The Royal Astronomical Society)

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Papers

  • High‐Resolution Fault‐Rupture Imaging by Combining a Backprojection Method With Binarized MUSIC Spectral Image Calculation Reviewed

    Mitsutaka Oshima, Hiroshi Takenaka, Makoto Matsubara

    Journal of Geophysical Research: Solid Earth   127 ( 11 )   2022.11

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union (AGU)  

    DOI: 10.1029/2022jb024003

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022JB024003

  • Enhancement of direct waves based on the probability density function of seismic wave amplitudes Reviewed

    Mitsutaka Oshima, Hiroshi Takenaka

    Geophysical Journal International   231 ( 1 )   327 - 354   2022.6

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Oxford University Press (OUP)  

    SUMMARY

    The enhancement of direct waves in seismic records is desirable in various seismological situations, where the accurate picking of seismic phases is necessary for hypocentre location, spectral inversion, waveform inversion and seismic tomography. In this study, we developed a new method to enhance direct waves in seismic waveforms based on the statistical distribution (probability density function, PDF) of the amplitudes of waveforms. The seismic waveform changes from a direct wave to a coda wave as time proceeds, which also causes the PDF of its amplitude to vary with time. The PDF becomes similar to a Gaussian or Rayleigh distribution with time, and hence, direct waves can be enhanced using the dissimilarity between the PDF of the amplitude of the seismic waveform and the Gaussian or Rayleigh distribution. In the proposed method, the Kullback–Leibler divergence is used to measure dissimilarity and it is applied as a weight. We confirmed that the method can effectively enhance direct P and S waves by applying it to seismic records of the 2016 Kumamoto earthquake, synthetic waveforms with noise and volcanic events. The method was also applied to waveforms of the 2008 Iwate–Miyagi Nairiku earthquake, which revealed that direct waves were enhanced, and an overview of the wave field and rupture process was obtained. The proposed method can detect direct waves even from subevents, thereby producing detailed information on the earthquake rupture process. We detected two significant pulses and determined their source location and rupture times. The estimated pulse sources were consistent with parts of the rupture scenario proposed by the previous studies. In addition, for local and teleseismic event records, the proposed method was compared with other methods to study its merits and demerits. The present method can enhance seismic phases on records of local and teleseismic events. Our method detects or enhances direct waves based neither on their amplitudes nor on their temporal variations but on the statistical distribution of their amplitudes, which has both advantages and disadvantages. Although polarization filtering is a powerful method that can enhance seismic phases, it requires three-component waveforms. The proposed method can be applied even to a single component record, which is a significant advantage.

    DOI: 10.1093/gji/ggac193

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    Other Link: https://academic.oup.com/gji/article-pdf/231/1/327/44160493/ggac193.pdf

  • Estimation of Seismic Attenuation of the Greenland Ice Sheet Using 3-D Waveform Modeling Reviewed

    Genti Toyokuni, Masanao Komatsu, Hiroshi Takenaka

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   126 ( 4 )   2021.4

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    We estimated the seismic attenuation (Q factor) of the Greenland Ice Sheet (GrIS) by comparing observed and theoretical Rayleigh waveforms. Observed waveforms are obtained by interfering noise waveforms in vertical-component seismograms between stations belonging to the latest broadband seismic network distributed throughout Greenland (GLISN network). Theoretical waveforms are calculated by parallel computation using the latest 3-D seismic waveform modeling method. Comparing the observed waveforms with the theoretical waveforms at different Q factors reveals that the GrIS has a low Q of 10 <= Q(P), Q(S) <= 50, indicating very high attenuation of seismic waves due to the ice. This study is the first to establish the low Q factor of ice sheets via ultra-long-distance propagation (350-1,000 km). The Q factors obtained in this study are indispensable for estimating the thermal state and density distribution of the GrIS, as well as for interpreting the characteristics of seismic waveform that propagates through the GrIS.Plain Language Summary Seismic anelastic attenuation refers to the energy loss caused by anelastic processes or internal friction during wave propagation and is quantified by the quality (Q) factor. The Q factor of ice sheets and glacial ice is especially important because it is highly sensitive to the thermal state and density distribution. We estimated the Q factor of the Greenland Ice Sheet (GrIS) by comparing observed and theoretical surface (Rayleigh) waveforms. Observed waveforms are extracted by the latest broadband seismic network distributed throughout Greenland (GLISN network). Theoretical waveforms are calculated using the latest 3-D seismic waveform modeling method. The results showed an extremely low Q (10-50) for the GrIS, indicating very high attenuation of seismic waves. Although previous studies have obtained similar results, they all used high frequency (>= 30 Hz) seismic waves with short propagation distances (<similar to 10 km). This study is the first to infer the large-scale, bulk Q property of the GrIS using low-frequency (0.1-0.3 Hz) waves and long (350-1,000 km) propagation distances. The Q factors obtained in this study are essential for estimating the internal state of the GrIS, as well as for interpreting the characteristics of seismic waveforms that propagate through it.

    DOI: 10.1029/2021JB021694

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  • DEEP SUBSURFACE S-WAVE VELOCITY STRUCTURE OF OKINAWA ISLANDS, JAPAN—FOR NUMERICAL MODELING Reviewed

    Nobuyuki YAMADA, Hiroshi TAKENAKA

    Journal of Japan Association for Earthquake Engineering   21 ( 3 )   3_119 - 3_134   2021

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Japan Association for Earthquake Engineering  

    DOI: 10.5610/jaee.21.3_119

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  • A P- and S-Wave Picking Technique Based on the Probabilistic Density Function of Seismic Waveform Amplitude (vol 110, pg 763, 2020)

    Mitsutaka Oshima, Hiroshi Takenaka

    BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA   110 ( 6 )   3211 - 3212   2020.12

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    Authorship:Last author   Language:English   Publisher:SEISMOLOGICAL SOC AMER  

    DOI: 10.1785/0120200291

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  • A P- and S-Wave Picking Technique Based on the Probabilistic Density Function of Seismic-Waveform Amplitude Reviewed

    Mitsutaka Oshima, Hiroshi Takenaka

    BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA   110 ( 2 )   763 - 782   2020.4

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:SEISMOLOGICAL SOC AMER  

    Picking of P and S waves is a fundamental process in seismology, and various kinds of picking techniques have been developed. Seismic waveforms change dramatically depending on the magnitude, the mechanism of the earthquake, and the positional relationship between the hypocenter and the seismic station.The availability of various picking techniques is supposed to be helpful for appropriately dealing with a variety of seismic records. Hence, in addition to the revision of conventional techniques, the development of new picking techniques is worthwhile. In the present study, we developed a new stochastic technique to detect P and S waves based on the statistical amplitude distribution in the seismic record amplitude.In the proposed method, the probabilistic density function (PDF) of the amplitude is calculated for each segment of seismic records, and the similarity between the PDF of the amplitude and that of the Rayleigh or Gaussian distribution is evaluated by divergence. Because Rayleigh and Gaussian distributions are typically found in amplitude distributions of highly random waves, such as coda waves, the divergence indicates the randomness of the seismic records. P and S waves are found by tracing the temporal change of the divergence.We tested the proposed method using local seismic records for a series of seismic events that occurred before and after the 2016 Kumamoto earthquake. The mean absolute errors for picking P and S waves are 2.72 x 10(-2) and 7.38 x 10(-2) s, respectively. The proposed method is a simple and new statistical picking method that enables automatic detection of P- and S-wave arrivals.

    DOI: 10.1785/0120190078

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  • Deep Subsurface S-wave Structure of Okinawa Islands, Japan Reviewed

    Nobuyuki YAMADA, Hiroshi TAKENAKA

    Journal of Japan Association for Earthquake Engineering   19 ( 4 )   4_156 - 4_169   2019.8

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    Authorship:Last author   Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Japan Association for Earthquake Engineering  

    DOI: 10.5610/jaee.19.4_156

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  • Evaluation of accuracy of synthetic waveforms for subduction-zone earthquakes by using a land-ocean unified 3D structure model Reviewed

    Taro Okamoto, Hiroshi Takenaka, Takeshi Nakamura

    EARTH PLANETS AND SPACE   70   2018.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    Seismic wave propagation from shallow subduction-zone earthquakes can be strongly affected by 3D heterogeneous structures, such as oceanic water and sedimentary layers with irregular thicknesses. Synthetic waveforms must incorporate these effects so that they reproduce the characteristics of the observed waveforms properly. In this paper, we evaluate the accuracy of synthetic waveforms for small earthquakes in the source area of the 2011 Tohoku-Oki earthquake (M-JMA 9.0) at the Japan Trench. We compute the synthetic waveforms on the basis of a land-ocean unified 3D structure model using our heterogeneity, oceanic layer, and topography finite-difference method. In estimating the source parameters, we apply the first-motion augmented moment tensor (FAMT) method that we have recently proposed to minimize biases due to inappropriate source parameters. We find that, among several estimates, only the FAMT solutions are located very near the plate interface, which demonstrates the importance of using a 3D model for ensuring the self-consistency of the structure model, source position, and source mechanisms. Using several different filter passbands, we find that the full waveforms with periods longer than about 10 s can be reproduced well, while the degree of waveform fitting becomes worse for periods shorter than about 10 s. At periods around 4 s, the initial body waveforms can be modeled, but the later large-amplitude surface waves are difficult to reproduce correctly. The degree of waveform fitting depends on the source location, with better fittings for deep sources near land. We further examine the 3D sensitivity kernels: for the period of 12.8 s, the kernel shows a symmetric pattern with respect to the straight path between the source and the station, while for the period of 6.1 s, a curved pattern is obtained. Also, the range of the sensitive area becomes shallower for the latter case. Such a 3D spatial pattern cannot be predicted by 1D Earth models and indicates the strong effects of 3D heterogeneity on short-period (less than or similar to 10s) waveforms. Thus, it would be necessary to consider such 3D effects when improving the structure and source models.

    DOI: 10.1186/s40623-018-0871-z

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  • Changes in Greenland ice bed conditions inferred from seismology Reviewed

    Genti Toyokuni, Hiroshi Takenaka, Ryota Takagi, Masaki Kanao, Seiji Tsuboi, Yoko Tono, Dean Childs, Dapeng Zhao

    PHYSICS OF THE EARTH AND PLANETARY INTERIORS   277   81 - 98   2018.4

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER  

    Basal conditions of the Greenland Ice Sheet (GrIS) are a key research topic in climate change studies. The recent construction of a seismic network has provided a new opportunity for direct, real-time, and continuous monitoring of the GrIS. Here we use ambient noise surface wave data from seismic stations all over Greenland for a 4.5-year period to detect changes in Rayleigh-wave phase velocity between seismic station pairs. We observe clear seasonal and long-term velocity changes for many pairs, and propose a plausible mechanism for these changes. Dominant factors driving the velocity changes might be seasonal and long-term pressurization/depressurization of the GrIS and shallow bedrock by air and ice mass loading/unloading. However, heterogeneity of the GrIS basal conditions might impose strong regionalities on the results. An interesting feature is that, even at adjacent two station pairs in the inland GrIS, one pair shows velocity decrease while another shows velocity increase as a response to the high air and snow pressure. The former pair might be located on a thawed bed that decreases velocity by increased meltwater due to pressure melting, whereas the latter pair might be located on a frozen bed that increases velocity by compaction of ice and shallow bedrock. The results suggest that surface waves are very sensitive to the GrIS basal conditions, and further observations will contribute to a more direct and quantitative estimation of water balance in the Arctic region.

    DOI: 10.1016/j.pepi.2017.10.010

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  • Deep Subsurface S-wave Structure of Sakishima (Miyako and Yaeyama) Islands, Southwestern Japan Reviewed

    Nobuyuki YAMADA, Hiroshi TAKENAKA

    Journal of Japan Association for Earthquake Engineering   18 ( 1 )   1_77 - 1_88   2018.2

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    Authorship:Last author   Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Japan Association for Earthquake Engineering  

    DOI: 10.5610/jaee.18.1_77

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  • Three-dimensional P- and S-wave attenuation structures around the source region of the 2016 Kumamoto earthquakes Reviewed

    Masanao Komatsu, Hiroshi Takenaka, Hitoshi Oda

    EARTH PLANETS AND SPACE   69   2017.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    We investigate the three-dimensional P- and S-wave attenuation (Q(P)(-1) and Q(S)(-1)) structures of the crust around the source region of the 2016 Kumamoto earthquakes, Japan. To estimate the attenuation structures, the path-averaged attenuation factor t* is estimated from the amplitude decay rate of the P- and S-wave spectra corrected for the source spectrum. The Q(P)(-1) and Q(S)(-1) structures are estimated by tomography using t* for the P- and S-waves, respectively. Several features are found in the attenuation structures as follows: In the source region, two high-Q(P) and high-Q(S) zones exist along the Futagawa and the Hinagu fault segments in the upper crust. The high-Q(P) and high-Q(S) zone along the Futagawa fault segment is found to include the large-slip area of the mainshock obtained from a source inversion study. In the lower crust, the low Q(P) is distributed beneath the entire source region. A low-Q(P) and low-Q(S) zone also exists beneath the Kuju and Aso volcanoes, which is consistent with the shallow limited depth extent of the seismogenic zone due to high temperature. The western edge of this zone adjoins the eastern edge of the high-Q(P) and high-Q(S) area, including the large-slip area.

    DOI: 10.1186/s40623-017-0683-6

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  • FDM simulation of earthquakes off western Kyushu, Japan, using a land-ocean unified 3D structure model Reviewed

    Taro Okamoto, Hiroshi Takenaka, Takeshi Nakamura, Tatsuhiko Hara

    EARTH PLANETS AND SPACE   69   2017.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    Seismic activity occurred off western Kyushu, Japan, at the northern end of the Okinawa Trough on May 6, 2016 (14:11 JST), 22 days after the onset of the 2016 Kumamoto earthquake sequence. The area is adjacent to the Beppu-Shimabara graben where the 2016 Kumamoto earthquake sequence occurred. In the area off western Kyushu, a M7.1 earthquake also occurred on November 14, 2015 (5:51 JST), and a tsunami with a height of 0.3 m was observed. In order to better understand these seismic activity and tsunamis, it is necessary to study the sources of, and strong motions due to, earthquakes in the area off western Kyushu. For such studies, validation of synthetic waveforms is important because of the presence of the oceanic water layer and thick sediments in the source area. We show the validation results for synthetic waveforms through nonlinear inversion analyses of small earthquakes (similar to M5). We use a land-ocean unified 3D structure model, 3D HOT finite-difference method ("HOT" stands for Heterogeneity, Ocean layer and Topography) and a multi-graphic processing unit (GPU) acceleration to simulate the wave propagations. We estimate the first-motion augmented moment tensor (FAMT) solution based on both the long-period surface waves and short-period body waves. The FAMT solutions systematically shift landward by about 13 km, on average, from the epicenters determined by the Japan Meteorological Agency. The synthetics provide good reproductions of the observed full waveforms with periods of 10 s or longer. On the other hand, for waveforms with shorter periods (down to 4 s), the later surface waves are not reproduced well, while the first parts of the waveforms (comprising P- and S-waves) are reproduced to some extent. These results indicate that the current 3D structure model around Kyushu is effective for generating full waveforms, including surface waves with periods of about 10 s or longer. Based on these findings, we analyze the 2015 M7.1 event using the cross-correlations between the observed and synthetic waveforms. The result suggests a rupture propagation toward the NNE, with a major radiation about 25 km north of the onset point.

    DOI: 10.1186/s40623-017-0672-9

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  • Quasi-Cartesian finite-difference computation of seismic wave propagation for a three-dimensional sub-global model Reviewed

    Hiroshi Takenaka, Masanao Komatsu, Genti Toyokuni, Takeshi Nakamura, Taro Okamoto

    EARTH PLANETS AND SPACE   69   2017.5

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    A simple and efficient finite-difference scheme is developed to calculate seismic wave propagation in a partial spherical shell model of a three-dimensionally (3-D) heterogeneous global Earth structure for modeling on regional or sub-global scales where the effects of the Earth's spherical geometry cannot be ignored. This scheme solves the elastodynamic equation in the quasi-Cartesian coordinate form similar to the local Cartesian one, instead of the spherical polar coordinate form, with a staggered-grid finite-difference method in time domain (FDTD) that is one of the most popular numerical methods in seismic-motion simulations for local-scale models. The proposed scheme may be a local-friendly approach for modeling on a sub-global scale to link regional-scale and local-scale simulations. It can be easily implemented using an available 3-D Cartesian FDTD local-scale modeling code by changing a very small part of the code. We implement the scheme in an existing Cartesian FDTD code and demonstrate the accuracy and validity of the present scheme and the feasibility to apply it to real large simulations through numerical examples.

    DOI: 10.1186/s40623-017-0651-1

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  • Special issue "The 2015 Gorkha, Nepal, earthquake and Himalayan studies: First results" PREFACE

    Hiroe Miyake, Soma Nath Sapkota, Bishal Nath Upreti, Laurent Bollinger, Tomokazu Kobayashi, Hiroshi Takenaka

    EARTH PLANETS AND SPACE   69   2017.1

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    Language:English   Publisher:SPRINGER HEIDELBERG  

    DOI: 10.1186/s40623-016-0597-8

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  • Long-period ocean-bottom motions in the source areas of large subduction earthquakes Reviewed

    Takeshi Nakamura, Hiroshi Takenaka, Taro Okamoto, Michihiro Ohori, Seiji Tsuboi

    SCIENTIFIC REPORTS   5   2015.11

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:NATURE PUBLISHING GROUP  

    Long-period ground motions in plain and basin areas on land can cause large-scale, severe damage to structures and buildings and have been widely investigated for disaster prevention and mitigation. However, such motions in ocean-bottom areas are poorly studied because of their relative insignificance in uninhabited areas and the lack of ocean-bottom strong-motion data. Here, we report on evidence for the development of long-period (10-20 s) motions using deep ocean-bottom data. The waveforms and spectrograms demonstrate prolonged and amplified motions that are inconsistent with attenuation patterns of ground motions on land. Simulated waveforms reproducing observed ocean-bottom data demonstrate substantial contributions of thick low-velocity sediment layers to development of these motions. This development, which could affect magnitude estimates and finite fault slip modelling because of its critical period ranges on their estimations, may be common in the source areas of subduction earthquakes where thick, low-velocity sediment layers are present.

    DOI: 10.1038/srep16648

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  • Global SH-wave propagation in a 2D whole Moon model using the parallel hybrid PSM/FDM method Reviewed

    Xianghua Jiang, Yanbin Wang, Yanfang Qin, Hiroshi Takenaka

    EARTHQUAKE SCIENCE   28 ( 3 )   163 - 174   2015.6

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER  

    We present numerical modeling of SH-wave propagation for the recently proposed whole Moon model and try to improve our understanding of lunar seismic wave propagation. We use a hybrid PSM/FDM method on staggered grids to solve the wave equations and implement the calculation on a parallel PC cluster to improve the computing efficiency. Features of global SH-wave propagation are firstly discussed for a 100-km shallow and 900-km deep moonquakes, respectively. Effects of frequency range and lateral variation of crust thickness are then investigated with various models. Our synthetic waveforms are finally compared with observed Apollo data to show the features of wave propagation that were produced by our model and those not reproduced by our models. Our numerical modeling show that the low-velocity upper crust plays significant role in the development of reverberating wave trains. Increasing frequency enhances the strength and duration of the reverberations. Surface multiples dominate wavefields for shallow event. Core-mantle reflections can be clearly identified for deep event at low frequency. The layered whole Moon model and the low-velocity upper crust produce the reverberating wave trains following each phases consistent with observation. However, more realistic Moon model should be considered in order to explain the strong and slow decay scattering between various phases shown on observation data.

    DOI: 10.1007/s11589-015-0121-4

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  • Numerical modeling of seismic waves for estimating the influence of the Greenland ice sheet on observed seismograms Reviewed

    Genti Toyokuni, Hiroshi Takenaka, Masaki Kanao, Seiji Tsuboi, Yoko Tono

    POLAR SCIENCE   9 ( 1 )   80 - 93   2015.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

    We calculate regional synthetic seismograms for a realistic structure model beneath Greenland, including surface topography and ice sheet thickness, for observations of the multinational GreenLand Ice Sheet monitoring Network (GLISN). The thick and heterogeneous Greenland ice sheet can cause distortion of the seismic waveforms observed at the GLISN stations on ice. We developed a numerical technique that calculates accurate regional seismic wavefields with low computational requirements. Here, we calculate the elastic wave propagation up to 2 Hz for four structural models of the Greenland ice sheet from a seismic source at various depths and with different mechanisms. Our computations for a realistic ice sheet model, the near-surface seismic source produced a very characteristic wave train with a group velocity smaller than the S-wavespeed in the ice, considered to be an ice-sheet guided S wave, developed by the superposition of post-critical reflections between the free surface and the ice bed. We named this wave "Le", analogous to the Lg wave, a crustally guided S wave. Furthermore, computation for a deeper seismic source resulted in reinforcement of the crustal Sg-coda wave with a group velocity range of similar to 3.1-2.6 km/s, which agrees with the characteristic waveform observed on the Greenland ice sheet. (C) 2014 Elsevier B.V. and NIPR. All rights reserved.

    DOI: 10.1016/j.polar.2014.12.001

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  • Anomalously large seismic amplifications in the seafloor area off the Kii peninsula Reviewed

    Takeshi Nakamura, Masaru Nakano, Naoki Hayashimoto, Narumi Takahashi, Hiroshi Takenaka, Taro Okamoto, Eiichiro Araki, Yoshiyuki Kaneda

    MARINE GEOPHYSICAL RESEARCH   35 ( 3 )   255 - 270   2014.9

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER  

    Seismic wave amplifications were investigated using strong-motion data obtained from the ground's surface (K-net) on the Kii peninsula (southwestern Japan) and from the network of twenty seismic stations on the seafloor (DONET) located off the peninsula near the Nankai trough. Observed seismograms show that seismic signals at DONET stations are significantly larger than those at K-net stations, independent of epicentral distances. In order to investigate the cause of such amplifications, seismic wavefields for local events were simulated using the finite-difference method, in which a realistic 3D velocity structure in and around the peninsula was incorporated. Our simulation results demonstrate that seismic waves are significantly amplified at DONET stations in relation to the presence of underlying low-velocity sediment layers with a total thickness of up to 10 km. Our simulations also show considerable variations in the degree of amplification among DONET stations, which is attributed to differences in the thickness of the sediment layers. The degree of amplification is relatively low at stations above thin sediment layers near the trough axis, but seismic signals are much more amplified at stations closer to the Kii peninsula, where sediment layers are thicker than those at the trough axis. Simulation results are consistent with observations. This study, based on seafloor observations and simulations, indicates that because seismic signals are amplified due to the ocean-specific structures, the magnitude of earthquakes would be overestimated if procedures applied to data observed at land stations are used without corrections.

    DOI: 10.1007/s11001-014-9211-2

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  • Seismic Wavefields in the Deep Seafloor Area from a Submarine Landslide Source Reviewed

    Takeshi Nakamura, Hiroshi Takenaka, Taro Okamoto, Yoshiyuki Kaneda

    PURE AND APPLIED GEOPHYSICS   171 ( 7 )   1153 - 1167   2014.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER BASEL AG  

    We use the finite difference method to simulate seismic wavefields at broadband land and seafloor stations for a given terrestrial landslide source, where the seafloor stations are located at water depths of 1,900-4,300 m. Our simulation results for the landslide source explain observations well at the seafloor stations for a frequency range of 0.05-0.1 Hz. Assuming the epicenter to be located in the vicinity of a large submarine slump, we also model wavefields at the stations for a submarine landslide source. We detect propagation of the Airy phase with an apparent velocity of 0.7 km/s in association with the seawater layer and an accretionary prism for the vertical component of waveforms at the seafloor stations. This later phase is not detected when the structural model does not consider seawater. For the model incorporating the seawater, the amplitude of the vertical component at seafloor stations can be up to four times that for the model that excludes seawater; we attribute this to the effects of the seawater layer on the wavefields. We also find that the amplification of the waveform depends not only on the presence of the seawater layer but also on the thickness of the accretionary prism, indicating low amplitudes at the land stations and at seafloor stations located near the trough but high amplitudes at other stations, particularly those located above the thick prism off the trough. Ignoring these characteristic structures in the oceanic area and simply calculating the wavefields using the same structural model used for land areas would result in erroneous estimates of the size of the submarine landslide and the mechanisms underlying its generation. Our results highlight the importance of adopting a structural model that incorporates the 3D accretionary prism and seawater layer into the simulation in order to precisely evaluate seismic wavefields in seafloor areas.

    DOI: 10.1007/s00024-013-0717-3

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  • Monitoring of the Greenland ice sheet using a broadband seismometer network: the GLISN project Reviewed

    Genti Toyokuni, Masaki Kanao, Yoko Tono, Tetsuto Himeno, Seiji Tsuboi, Dean Childs, Kent Anderson, Hiroshi Takenaka

    Antarctic Record   58 ( 1 )   1 - 18   2014.3

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    Global climate change is currently causing melting of the Greenland ice sheet. Recently, a new type of seismic event, referred to as a "glacial earthquake", has been recognized. Such earthquakes are generated by the movements of large masses of ice within the terminal regions of glacier, and represent a new approach for monitoring ice sheet dynamics. In 2009, the multinational GreenLand Ice Sheet monitoring Network (GLISN), a large broadband seismological network in and around Greenland, was initiated to monitor these events. Japan, a partner country of the GLISN project, has been sending a field team to Greenland each year since 2011, when a joint USA and Japanese team first established a dual seismic-GPS station (station code: ICESG-GLS2) on the Greenland ice sheet. In 2012, the same team contributed to the maintenance of ICESG-GLS2, as well as two other stations (NUUK and DY2G-GLS1). The quality of the long-period seismic waveform data obtained by these stations has been checked by comparing the data with global synthetic seismograms. Results indicate that the data from the three stations have not been substantially affected by noise, and that the quality is well controlled.

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  • Exploration of Deep S-Wave Velocity Structure in Fukuoka Area Reviewed

    YAMADA Nobuyuki, TAKENAKA Hiroshi

    Zisin (Journal of the Seismological Society of Japan. 2nd ser.)   67 ( 1 )   25 - 34   2014

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    DOI: 10.4294/zisin.67.25

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  • Modelling two-dimensional global seismic wave propagation in a laterally heterogeneous whole-Moon model Reviewed

    Yanbin Wang, Hiroshi Takenaka, Xianghua Jiang, Jianshe Lei

    GEOPHYSICAL JOURNAL INTERNATIONAL   192 ( 3 )   1271 - 1287   2013.3

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    The whole-Moon model was recently proposed by re-analyzing of lunar seismic data, which presumes efficient propagation of seismic waves within the Moon. However, common seismic body-wave or surface-wave phases observed for earthquake are absent or very weak in lunar seismic signals characterized by strong reverberations and coda. Hence, the process of seismic wave propagation in the Moon's interior is not well understood from limited lunar seismic data. We present numerical simulations of seismic body wave propagation in the whole Moon based on recently published whole-Moon model. Seismic wave equations are solved in a 2-D cross-section of spherical Moon with a staggered grid pseudospectral and finite difference hybrid method. Our simulation results provide the processes of seismic body wave propagation in the whole Moon for both deep and shallow moonquakes with sequential wavefield snapshots and synthetic waveforms. Effects of lateral heterogeneity on seismic wave propagation were investigated by simulations for a Moon tomographic model. Comparisons with the observed Apollo seismograms show that simulations predicted the arrivals of direct P and S waves and reproduced the reverberating nature of both direct and secondary waves. However, modelling with only the 1-D or tomographic model does not seem to be enough to produce the slow decay of energy in observations if other possible factors, such as scattering, are not considered in the model. Comparisons between different focal mechanisms suggest that great differences can be seen for the direct waves, but the structure model contributes significantly to the overall characteristics of synthetic seismograms. Numerical simulations demonstrated efficient propagation and interactions with various interfaces of seismic body waves within the whole Moon. Seismic energy propagating in the near surface low-velocity layer formed trapped waves, which propagate along the surface and appear as reverberations in the waveforms. Strength of the reverberations increases with dominant frequency and decreasing focal depth. Detectability of lunar seismic body-wave phases should be enhanced with deployment of very broad band seismometer network in the future lunar seismic experiment, which will further improve our knowledge of the Moon's interior.

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  • FDTD3C-A FORTRAN program to model multi-component seismic waves for vertically heterogeneous attenuative media Reviewed

    Arash JafarGandomi, Hiroshi Takenaka

    COMPUTERS & GEOSCIENCES   51   314 - 323   2013.2

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    Full-waveform seismic response of horizontally layered media can be calculated by semi-analytical methods. However, for gradient velocity and randomly heterogeneous structures the semi-analytical methods face difficulties. In such cases, numerical methods such as the finite-difference (FD) method have to be used. We develop an efficient numerical scheme to calculate plane-wave response of vertically heterogeneous attenuative media by applying Radon transform to the three-dimensional wave equation. The scheme employs fourth-order FD operator in space and second-order FD operator in time to solve the wave equation. In order to facilitate applicability of the scheme we introduce the FORTRAN code FDTD3C which implements the algorithm and provides multi-component response of the media to oblique incident P-, SV-, and SH-waves incoming from arbitrary azimuth. The calculated components are three particle velocity components in three Cartesian directions, and divergence and rotation of the wavefield. The code is extremely efficient and is capable of incorporating highly fluctuating subsurface velocity and attenuation models. This program is intended for all FD users who are concerned with full-waveform seismic modelling and inversion. Wide range of applicability of the code is demonstrated with a set of numerical examples. (c) 2012 Elsevier Ltd. All rights reserved.

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  • Seismic ground motion amplification in a 3D sedimentary basin: The effect of the vertical velocity gradient Reviewed

    Yanfang Qin, Yanbin Wang, Hiroshi Takenaka, Xianbing Zhang

    Journal of Geophysics and Engineering   9 ( 6 )   761 - 772   2012.12

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    Ground motion amplification in sedimentary basins has been observed in some moderate or large earthquakes, such as the 1994 Northridge and 1999 Chi-Chi event. Many numerical studies with simplified 2D models have shown significant effects of the vertical velocity gradient of sediment on basin amplification. However, we need to consider a more realistic 3D model and solve wave equations with 3D numerical methods in order to improve our understanding of basin amplification. In this study, we extend a 2D pseudospectral and finite difference hybrid method to a 3D case and investigate the effects of the vertical velocity gradient for a 3D basin model. Numerical simulations were performed for four basin models with increasing vertical velocity gradients on a PC cluster using 64 processors for 67 108 864 discretized grids. The results show that the vertical velocity gradient enhances basin amplification through strong secondary surface waves and basin trapped waves. The 3D geometry of the basin causes a wave-front focusing effect that contributes significantly to a localized strong amplification with the maximum peak ground velocity in the basin. The results of this study suggest that it is important to consider the detailed properties of sedimentary basins in seismic ground motion studies. © 2012 Sinopec Geophysical Research Institute.

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  • FDM simulation of seismic-wave propagation for an aftershock of the 2009 Suruga bay earthquake: Effects of ocean-bottom topography and seawater layer Reviewed

    Takeshi Nakamura, Hiroshi Takenaka, Taro Okamoto, Yoshiyuki Kaneda

    Bulletin of the Seismological Society of America   102 ( 6 )   2420 - 2435   2012.12

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    Feasibility studies on simulating seismic-wave propagation in media for a suboceanic earthquake, including both land and ocean-bottom topographies and a seawater layer, are scarce. Some of the conventional staggered-grid finite-difference method (FDM) simulations use a simplified structure model without a seawater layer and with a flat ocean-bottom topography. In this study, we apply our heterogeneity, oceanic layer, and topography scheme (HOT)-FDM and a 3D structure model including land and ocean-bottom topographies, a seawater layer, and a fluid-solid boundary condition to an aftershock (Mw 5.8) of the 2009 Suruga Bay earthquake.We attempt to reproduce observations at seismic stations near the coast and then simulate waveforms in the ocean-bottom stations. Our results show that a large difference between the cases with and without topographies can be seen in the coda part after the S wave in the simulated waveforms in terms of amplitudes and elongations. The synthetic waveforms in the model with topographies are in agreement with the observed waveforms. Our results also show that a significant difference in the amplification of the coda part between the cases with and without the seawater layer can be found at the ocean-bottom stations. This coda part is the S- and Rayleigh-wave propagation associated with the ocean and the underlying sediment layers. Our results show that a realistic model with topographies and a seawater layer is needed in FDM simulations in order to precisely reproduce observed waveforms or predict seismic motion for a suboceanic earthquake.

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  • Comparison of global synthetic seismograms calculated using the spherical 2.5-D finite-difference method with observed long-period waveforms including data from the intra-Antarctic region Reviewed

    Genti Toyokuni, Hiroshi Takenaka, Masaki Kanao, Douglas A. Wiens, Andrew Nyblade

    Polar Science   6 ( 2 )   155 - 164   2012.7

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    We have been developing an accurate and efficient numerical scheme, which uses the finite-difference method (FDM) in spherical coordinates, for the computation of global seismic wave propagation through laterally heterogeneous realistic Earth models. In the field of global seismology, traditional axisymmetric modeling has been used widely as an efficient approach since it can solve the 3-D elastodynamic equation in spherical coordinates on a 2-D cross-section of the Earth, assuming structures to be invariant with respect to the axis through the seismic source. However, it has the severe disadvantages that asymmetric structures about the axis cannot be incorporated and the source mechanisms with arbitrary shear dislocation have not been attempted for a long time. Our scheme is based on the framework of axisymmetric modeling but has been extended to treat asymmetric structures, arbitrary moment-tensor point sources, anelastic attenuation, and the Earth center which is a singularity of wave equations in spherical coordinates. All these types of schemes which solve 3-D wavefields on a 2-D model cross-section are classified as 2.5-D modeling, so we have named our scheme the spherical 2.5-D FDM. In this study, we compare synthetic seismograms calculated using our FDM scheme with three-component observed long-period seismograms including data from stations newly installed in Antarctica in conjunction with the International Polar Year (IPY) 2007-2008. Seismic data from inland Antarctica are expected to reveal images of the Earth's deep interior with enhanced resolution because of the high signal-to-noise ratio and wide extent of this region, in addition to the rarity of sampling paths along the rotation axis of the Earth. We calculate synthetic seismograms through the preliminary reference earth model (PREM) including attenuation using a moment-tensor point source for the November 9, 2009 Fiji earthquake. Our results show quite good agreement between synthetic and observed seismograms, which indicates the accuracy of observations in the Antarctica, as well as the feasibility of the spherical 2.5-D modeling scheme. © 2012 Elsevier B.V. and NIPR.

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  • Accurate and efficient modeling of global seismic wave propagation for an attenuative Earth model including the center Reviewed

    Genti Toyokuni, Hiroshi Takenaka

    Physics of the Earth and Planetary Interiors   200-201   45 - 55   2012.6

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    We propose a method for modeling global seismic wave propagation through an attenuative Earth model including the center. This method enables accurate and efficient computations since it is based on the 2.5-D approach, which solves wave equations only on a 2-D cross section of the whole Earth and can correctly model 3-D geometrical spreading. We extend a numerical scheme for the elastic waves in spherical coordinates using the finite-difference method (FDM), to solve the viscoelastodynamic equation. For computation of realistic seismic wave propagation, incorporation of anelastic attenuation is crucial. Since the nature of Earth material is both elastic solid and viscous fluid, we should solve stress-strain relations of viscoelastic material, including attenuative structures. These relations represent the stress as a convolution integral in time, which has had difficulty treating viscoelasticity in time-domain computation such as the FDM. However, we now have a method using so-called memory variables, invented in the 1980s, followed by improvements in Cartesian coordinates. Arbitrary values of the quality factor (Q) can be incorporated into the wave equation via an array of Zener bodies. We also introduce the multi-domain, an FD grid of several layers with different grid spacings, into our FDM scheme. This allows wider lateral grid spacings with depth, so as not to perturb the FD stability criterion around the Earth center. In addition, we propose a technique to avoid the singularity problem of the wave equation in spherical coordinates at the Earth center. We develop a scheme to calculate wavefield variables on this point, based on linear interpolation for the velocity-stress, staggered-grid FDM. This scheme is validated through a comparison of synthetic seismograms with those obtained by the Direct Solution Method for a spherically symmetric Earth model, showing excellent accuracy for our FDM scheme. As a numerical example, we apply the method to simulate seismic waves affected by hemispherical variations of P-wavespeed and attenuation in the top 300. km of the inner core. © 2012 Elsevier B.V..

    DOI: 10.1016/j.pepi.2012.03.010

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  • SH-wavefield simulation for a laterally heterogeneous whole-Earth model using the pseudospectral method Reviewed

    YanBin Wang, Hiroshi Takenaka

    Science China Earth Sciences   54 ( 12 )   1940 - 1947   2011.12

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    We present a scheme to simulate SH-wave propagation in a whole-Earth model with arbitrary lateral heterogeneities employing the Fourier pseudospectral method. Wave equations are defined in two-dimensional cylindrical coordinates and the model is taken through a great circle of the Earth. Spatial derivatives in the wave equations are calculated in the wavenumber domain by multiplication, and the transformation between spatial and wavenumber domains is performed via fast Fourier transformation. Because of the high accuracy and high speed of the Fourier pseudospectral method, the scheme enables us to calculate a short-wavelength global SH-wavefield with accurate waveforms and arrival times for models with heterogeneities that can be approximated as azimuthally symmetric. Comparing with two-dimensional simulation methods based on an axisymmetric model, implementing the seismic source in the present scheme is more convenient. We calculated the global SH-wavefield for the preliminary reference Earth model to identify the generation, reflection and refraction of various seismic phases propagating in the Earth. Applications to a heterogeneous global model with low-velocity perturbation above the core-mantle boundary were conducted to analyze the effect of lateral heterogeneity on global SH-wave propagation. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.

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  • A Study of the Finite Difference Solution for 3D Seismic Wavefields near a Fluid-Solid Interface Reviewed

    NAKAMURA Takeshi, TAKENAKA Hiroshi, OKAMOTO Taro, KANEDA Yoshiyuki

    Zisin (Journal of the Seismological Society of Japan. 2nd ser.)   63 ( 3 )   189 - 196   2011

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  • A scheme to treat the singularity in global seismic wavefield simulation using pseudospectral method with staggered grids Reviewed

    Yanbin Wang, Hiroshi Takenaka

    Earthquake Science   23 ( 2 )   121 - 127   2010.4

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    The pseudospectral method has been applied to the simulation of seismic wave propagation in 2-D global Earth model. When a whole Earth model is considered, the center of the Earth is included in the model and then singularity arises at the center of the Earth where r = 0 since the 1/r term appears in the wave equations. In this paper, we extended the global seismic wavefield simulation algorithm for regular grid mesh to staggered grid configuration and developed a scheme to solve the numerical problems associated with the above singularity for a 2-D global Earth model defined on staggered grid using pseudospectral method. This scheme uses a coordinate transformation at the center of the model, in which the field variables at the center are calculated in Cartesian coordinates from the values on the grids around the center. It allows wave propagation through the center and hence the wavefield at the center can be stably calculated. Validity and accuracy of the scheme was tested by compared with the discrete wavenumber method. This scheme could also be suitable for other numerical methods or models parameterized in cylindrical or spherical coordinates when singularity arises at the center of the model.

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  • Three component 1D viscoelastic FDM for plane-wave oblique incidence Reviewed

    Arash Jafargandomi, Hiroshi Takenaka

    Advances in Geosciences: Volume 20: Solid Earth (SE)   299 - 312   2010.1

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    We propose a very efficient scheme for modeling three-component seismic plane waves in vertically heterogeneous attenuative media using the finitedifference (FD) method in the time domain. The scheme is able to represent P, SV, and SH waves incoming from different direction. The algorithm can also calculate the plane-wave responses of media for different incident angels. In the algorithm, neglecting lateral heterogeneity, the wave equation is rewritten for plane waves by applying a 2D Radon transform to the 3D general wave equation. QP and QS are incorporated via generalized Zener body rheological models for viscoelasticity to represent anelastic attenuation. Our FD scheme uses a 1D grid, which leads to a significant reduction in computation time and memory requirements as compared to the corresponding 3D or 2D computations. It may be an efficient tool for pre- or post-analysis of local structural effects including anelastic attenuation, before or after the large-scale seismic wave simulation. To demonstrate the ability and efficiency of the scheme, we calculate a synthetic vertical seismic profile (VSP) for a borehole with a highly heterogeneous velocity model and frequency dependent attenuation model in the Kanto area of Japan.

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  • Accelerating large-scale simulation of seismic wave propagation by multi-GPUs and three-dimensional domain decomposition Reviewed

    Taro Okamoto, Hiroshi Takenaka, Takeshi Nakamura, Takayuki Aoki

    Earth, Planets and Space   62 ( 12 )   939 - 942   2010

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    We adopted the GPU (graphics processing unit) to accelerate the large-scale finite-difference simulation of seismic wave propagation. The simulation can benefit from the high-memory bandwidth of GPU because it is a "memory intensive" problem. In a single-GPU case we achieved a performance of about 56 GFlops, which was about 45-fold faster than that achieved by a single core of the host central processing unit (CPU). We confirmed that the optimized use of fast shared memory and registers were essential for performance. In the multi-GPU case with three-dimensional domain decomposition, the non-contiguous memory alignment in the ghost zones was found to impose quite long time in data transfer between GPU and the host node. This problem was solved by using contiguous memory buffers for ghost zones. We achieved a performance of about 2.2 TFlops by using 120 GPUs and 330 GB of total memory: nearly (or more than) 2200 cores of host CPUs would be required to achieve the same performance. The weak scaling was nearly proportional to the number of GPUs. We therefore conclude that GPU computing for large-scale simulation of seismic wave propagation is a promising approach as a faster simulation is possible with reduced computational resources compared to CPUs. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Science (SGEPSS).

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  • ACE-A FORTRAN subroutine for analytical computation of effective grid parameters for finite-difference seismic waveform modeling with standard Earth models Reviewed

    Genti Toyokuni, Hiroshi Takenaka

    Computers and Geosciences   35 ( 3 )   635 - 643   2009.3

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    Despite the broad use of the heterogeneous finite-difference (FD) method for seismic waveform modeling, accurate treatment of material discontinuities inside the grid cells has been a serious problem for many years. One possible way to solve this problem is to introduce effective grid elastic moduli and densities (effective parameters) calculated by the volume harmonic averaging of elastic moduli and volume arithmetic averaging of densities in grid cells. This scheme enables us to place a material discontinuity in an arbitrary position in the spatial grids. Standard Earth models have made a significant contribution to synthetic seismogram calculations with a variety of numerical procedures such as the FD method. For the FD computation of seismic waveform with these models, we must first ensure accurate treatment of material discontinuities in the radius (or depth). The present paper introduces a FORTRAN subroutine ACE which calculates effective parameters analytically for an arbitrary spatial region in either the radius or depth direction for four major standard Earth models, namely, the PREM, IASP91, SP6, and AK135. This program is intended for all FD users who are concerned with seismic wave simulation for these models. © 2008 Elsevier Ltd. All rights reserved.

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  • Effect of near-source trench structure on teleseismic body waveforms: An application of a 2.5D FDM to the Java trench Reviewed

    Taro Okamoto, Hiroshi Takenaka

    Advances in Geosciences: Volume 13: Solid Earth (SE)   215 - 230   2009.1

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    We study strong effect of near-source structure on teleseismic body waveforms from two well-recorded aftershocks of the 2006 Java tsunami earthquake. We assume a two-dimensional, heterogeneous model of the Java trench structure on the basis of recent seismic surveys. We compute synthetic waveforms by an efficient “2.5-dimensional” (2.5D) finite-difference method. A “waveform relocation technique” which combines a non-linear inversion of source parameters with a grid search procedure is applied in order to correct possible systematic bias in hypocentral parameters. Simulation of inversion shows that the resolution of the source position obtained by using 2.5D Green’s functions is better than that for 1D Green’s functions. The synthetic waveforms obtained by the inversion of true data with 2.5D Green’s functions reproduce well the observed large later phases, and retrieved moment tensors are similar to those of Global CMT. Thus, the effect of the near-source structure can be reproduced by 2.5D model, and with the 2.5D synthetics we can obtain improved source parameters at the trench regions where only teleseismic data are available.

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  • Waveform inversion for slip distribution of the 2006 Java tsunami earthquake by using 2.5D finite-difference Green&apos;s function Reviewed

    Taro Okamoto, Hiroshi Takenaka

    EARTH PLANETS AND SPACE   61 ( 5 )   E17 - E20   2009

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    We first incorporate the large effect of near-source heterogeneity on teleseismic body waveforms in the inversion of the slip distribution of the 2006 Java tsunami earthquake. We incorporate the effect by computing the response of an assumed "2.5D" model structure of the Java trench by a 2.5D finite-difference method. Based on a simulation of inversion, we suggest that intense smearing is possible when we apply 1D Green&apos;s functions in the analysis, and that it may obscure the slip pattern. In the inversion of real data, we confirm macroscopic features, such as a long duration (similar to 165 s) and a slow rupture velocity (similar to 1.25 km/s). The region of the initial rupture is found to be isolated from the eastern broad region in which we further identify a heterogeneous slip distribution. Most of these regions are likely to be at the sedimentary plate interface where the accreted sediment and the subducting plate are in contact. In particular, the nearly "isolated" feature of a shallow slip region suggests a possible faulting in the shallowest part of the sedimentary plate interface without being strongly enforced by the rupture propagated from the deeper part of the fault. Such heterogeneity suggests a highly variable frictional behavior at the sedimentary plate interface.

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  • Rupture process at the beginning of the 2007 Chuetsu-oki, Niigata, Japan, earthquake Reviewed

    Hiroshi Takenaka, Yosuke Yamamoto, Hirokazu Yamasaki

    EARTH PLANETS AND SPACE   61 ( 2 )   279 - 283   2009

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    The rupture process at the beginning stage of the 2007 Chuetsu-oki, Niigata, Japan, earthquake (M(w), 6.6) is investigated by analyzing P-wave records from local strong-motion stations. The P-wave portion of the near-source strong-motion records shows about 2 s of small but increasing amplitude arrival (so-called "initial rupture phase") followed by the onset of the main energy release ("main rupture phase"), Two issues are addressed in this paper: (I) where the initial rupture process occurred and (2) where the seismic energy corresponding to the main rupture phase was released at the primary stage of the main rupture. The first Issue is addressed by locating the main rupture onset position, and the second issue is then approached by introducing a method for mapping the wave energy onto plausible fault planes. Eventually, the following were revealed, The rupture initiated and propagated oil the NW-dipping plane, which is a nodal plane of the focal mechanism Solution. At 2.1 s after rupture initiation the subsequent main rupture started at a position of approximately 4 km away. southwestward and updipward from the hypocenter. The main rupture at this stage has two possible rupture planes: the same plane as the initial rupture plane, and the Conjugated plane, which shares the main rupture onset point with the initial rupture plane. Although it is difficult to determine which plane was actually ruptured at the primary stage of the main rupture, we found that the possible areas radiating strong wave energy oil the two possible planes, which could correspond to the first asperity of this earthquake, are located between the hypocenter and the Kashiwazaki-Kariwa nuclear power plant.

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  • Stochastic ground motion simulation of the 12 October 1992 Dahshour earthquake Reviewed

    Sayed S.R. Moustafa, Hiroshi Takenaka

    Acta Geophysica   57 ( 3 )   636 - 656   2009

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    The stochastic method for finite faults is applied to simulate the ground motion of the 12 October 1992, m b = 5.9, Dahshour earthquake. The method includes discritization of the fault plane into certain number of subfaults, and a ω-squared spectrum is assigned to each of them. Contributions from all subfaults are then empirically attenuated to the observation sites, where they are summed to produce the synthetic acceleration time-history. The method is first tested against its ability of reproducing the recording at Kottamya station. The calibrated model is then applied to calculate the synthetics at a large number of grid points covering the area around the fault plane. Simulated peak values are subsequently used to produce the synthetic peak horizontal acceleration map for the area. We compare the peak horizontal acceleration with the attenuation laws proposed for Egypt as well as the macroseismic intensity map of the 1992 Dahshour earthquake. The peak horizontal acceleration contours estimated using the calibrated model are mostly consistent with the observed intensity values and evidences of strong ground motions. Our results encourage the application of the approach as a supplementary tool for site-specific strong ground motion prediction. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.

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  • Non-standard FDTD for elastic wave simulation: Two-dimensional P-SV case Reviewed

    Arash JafarGandomi, Hiroshi Takenaka

    Geophysical Journal International   178 ( 1 )   282 - 302   2009

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    A scheme for the non-standard finite-difference method in the time-domain (NS-FDTD), 2-Box scheme, is proposed for elastic wave simulations in two dimensions (P-SV). The method improves the accuracy and efficiently reduces grid dispersion and anisotropy. The proposed non-standard scheme is based on two main operations. The first operation replaces spatial grid spacing and time step by their frequency optimized counterparts, called the correction functions, and the second operation introduces an optimum grid stencil for the finite-difference operator of the 2-D Laplacian. The optimal stencil is obtained by introducing two optimization parameters estimated for a design frequency. Error analysis of the proposed scheme (2-Box scheme) shows that specifying the maximum frequency as the design frequency leads to a significant reduction of the grid dispersion over a wide frequency band. We derive the formulations of grid dispersion and stability condition for the scheme. The grid dispersion is investigated, and it is shown that the proposed scheme reduces not only the grid dispersion but also the grid anisotropy significantly. The grid dispersion is insensitive to the Poisson's ratio and size of the time step within the stability limit. Since the wide spatial stencil of the 2-Box scheme might become difficult to implement at the computational domain boundaries, two additional non-standard schemes - 1-Box and 0-Box schemes - are also introduced. The 1-Box scheme uses narrower stencil than the 2-Box scheme, and the 0-Box scheme uses the same stencil as the standard FDTD. Numerical experiments of elastic wave propagation demonstrate the significant superiority of the proposed non-standard schemes over the commonly used standard one. With six grid spacings per minimum wavelength, the 2-Box and 1-Box schemes represent excellent results and the 0-Box scheme has higher accuracy than the standard scheme with seven grid spacings per minimum wavelength. © 2009 The Authors, Journal compilation © 2009 RAS.

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  • Source Modeling of the 2007 Niigataken Chuetsu-oki Earthquake Using the Empirical Green's Function Method Reviewed

    YAMAMOTO Yosuke, TAKENAKA Hiroshi

    Zisin (Journal of the Seismological Society of Japan. 2nd ser.)   62 ( 2 )   137 - 138   2009

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  • A compact representation of spatio-temporal slip distribution on a rupturing fault Reviewed

    Hiroshi Takenaka, Yushiro Fujii

    Journal of Seismology   12 ( 2 )   281 - 293   2008.4

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    We propose a mathematical representation to qualitatively describe the spatio-temporal slip evolution during earthquake rupture in an efficient and easy-to-use manner for numerical simulations of strong ground motion. It is based on three basis functions and associated expansion coefficients. It is an extension of the approach of Ide and Takeo, (J Geophys Res, 102:27379-27391, 1997). We compare our approach and theirs using simple kinematic source models to illustrate differences between the two approaches, and show that our approach more accurately represents the spatio-temporal slip evolution. We also propose a technique based on our representation for extracting a spatio-temporal slip velocity function from a kinematic source model obtained by the conventional source inversion. We then demonstrate the feasibility of our procedure with application to an inverted source model of the 26 March 1997 Northwestern Kagoshima, Japan, earthquake (MW 6.1). In the simulations for actual earthquakes, source models obtained from kinematic source inversions are commonly employed. Our scheme could be used as an interpolation method of slip time functions from relatively coarse finite-source models obtained by conventional kinematic source inversions. © Springer Science+Business Media B.V. 2008.

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  • A study of characters of the Umi fault along the eastern margin of the Fukuoka Plain, southwest Japan Reviewed

    Shimoyama Shoichi, Matsusue Kazuyuki, Matsuyama Hisanori, Yamamori Kunio, Iso Nozomi, Chida Noboru, Okamura Makoto, Matsuoka Hiromi, Ikeda Yasutaka, Matsuda Tokihiko, Takenaka Hiroshi, Ishimura Daisuke

    Active Fault Research   2008 ( 29 )   59 - 70   2008

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    The Umi fault was first described by Ikeda et al. (2004) as an active fault'of about 9km in length. Fukuoka Prefectural Government organized a research committee for examination and investigation of the Umi fault in 2005. The present study is based on air-photograph analysis, geological and topographical field surveys, soundreflection surveys in the marine areas, drilling and trenching, and tephrochronological studies. Some characters of the Umi fault are clarified through this intensive study.<BR>The Umi fault extends father north and south than was previously known, but it does not extend as far north as Hakata Bay and the Genkainada Sea. The length of the fault is 17km at least. The average vertical slip rate in the late Quaternary is estimated to be 0.02-0.03m/kyr (Activity Rank C in Matsuda 1975). This slip rate of the Umi fault is lower than those of the neighboring Kego and Nishiyama faults. The last activity of the fault was confirmed to be younger than 4300y. B. P. by the trenching study at Yamaura.<BR>The average recurrence interval of the activity is estimated at 29 kyr. This estimation is based on the assumption that the observed slip at the Yamaura trench (0.6m) occurred in one earthquake event and that the slip at Uenohara (1.9m), which is observed on middle terrace surface, formed immediately after the Aso-4 pyroclastic flow, is a result of repeated earthquake events of the same size slip.

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  • Efficient FDTD algorithm for plane-wave simulation for vertically heterogeneous attenuative media (vol 72, pg H43, 2007)

    Arash Jafar-Gandomi, Hiroshi Takenaka

    GEOPHYSICS   72 ( 6 )   Y7 - Y7   2007.11

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    DOI: 10.1190/1.2817659

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  • Efficient FDTD algorithm for plane-wave simulation for vertically heterogeneous attenuative media Reviewed

    Arash JafarGandomi, Hiroshi Takenaka

    GEOPHYSICS   72 ( 4 )   H43 - H53   2007.7

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    We propose an efficient algorithm for modeling seismic plane-wave propagation in vertically heterogeneous viscoelastic media using a finite-difference tirne-domain (FDTD) technique. In the algorithm, the wave equation is rewritten for plane waves by applying a Radon transform to the 2D general wave equation. Arbitrary values of the quality factor for P- and S-waves (Q(p) and Q(s)) are incorporated into the wave equation via a generalized Zener body rheological model. An FDTD staggered-grid technique is used to numerically solve the derived plane-wave equations. The scheme uses a 1 D grid that reduces computation time and memory requirements significantly more than corresponding 2D or 3D computations. Comparing the finite-difference solutions to their corresponding analytical results, we find that the methods are sufficiently accurate. The proposed algorithm is able to calculate synthetic waveforms efficiently and represent viscoelastic attenuation even in very attenuative media. The technique is then used to estimate the plane-wave responses of a sedimentary system to normal and inclined incident waves in the Kanto area of Japan via synthetic vertical seismic profiles.

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  • Evidence for a metastable olivine wedge inside the subducted Mariana slab Reviewed

    Satoshi Kaneshima, Taro Okamoto, Hiroshi Takenaka

    Earth and Planetary Science Letters   258 ( 1-2 )   219 - 227   2007.6

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    An anomalous seismic velocity structure is revealed inside the subducted Pacific plate at northern Mariana near the deepest earthquake foci. We observe anomalous later phases in the P wave coda for a small cluster of deep earthquakes and an anomalous differential P wave slowness between a few pairs of the earthquakes belonging to the cluster. We interpret these observations with a 5% low velocity wedge which is nearly 25 km wide at the depth of 590 km and is truncated at 630 km. The wedge is bounded by two steeply dipping (60°-70°) transition layers with the thickness of about 4 km. The highly localized seismic anomaly inside the slab represents a wedge of metastable olivine (α) embedded in dry ringwoodite (γ). Deep earthquakes occur across only one of the boundaries of the metastable wedge, with some of them outside the wedge. The mechanism of deep earthquakes is discussed based on the spatial pattern of seismicity relative to the wedge. © 2007 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.epsl.2007.03.035

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  • FDM computation of seismic wavefield for an axisymmetric earth with a moment tensor point source Reviewed

    Genti Toyokuni, Hiroshi Takenaka

    EPS   58 ( 12 )   e29 - e32   2006.12

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    DOI: 10.1186/BF03352593

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  • A numerical analysis of seismic waves for an anisotropic fault zone Reviewed

    Takeshi Nakamura, Hiroshi Takenaka

    Earth, Planets and Space   58 ( 5 )   569 - 582   2006

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    In this study we examine the effects of anisotropy on the seismic wavefield in a fault zone from computation of the synthetic seismograms for a simple fault zone model and a variety of seismic wave sources. The fault zone is modeled by a homogeneous vertical layer with transverse isotropy, induced by cracks, sandwiched between isotropic half-spaces (host rocks). The symmetry axis of the transverse isotropy is horizontal and perpendicular to the fault zone strike. We calculate the synthetic seismograms for this anisotropic fault zone model using a semi-analytical method, the propagator matrix method. The synthetic seismograms show a later phase arriving after the main shear-wave in the horizontal component perpendicular to the fault zone strike at most stations near the fault zone. It is the slower shear-wave (q S2) and its reverberation. The amplitude of this phase and the time delay from the main shear-wave arrival are proportional to the degree of anisotropy, which suggests that observing such phase in field measurements may imply the presence of an anisotropic fault zone. We also perform the shear-wave splitting measurements by applying the cross-correlation method to the synthetic seismograms for various sources. For a strike-slip source, the synthetic seismograms show that the wavefield is more affected by the velocity structure than by the degree of anisotropy, which makes it difficult to estimate the anisotropic (shear-wave splitting) parameters. For normal and dip-slip fault sources with the strike parallel to or striking against the fault zone, the effects of anisotropy is so dominant that the anisotropic fault zone can be detected. These results suggest that the determination of the anisotropic properties in the fault zone would require an appropriate station deployment and the source type information. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)
    The Seismological Society of Japan
    The Volcanological Society of Japan
    The Geodetic Society of Japan
    The Japanese Society for Planetary Sciences
    TERRAPUB.

    DOI: 10.1186/BF03351954

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  • Precise location of the fault plane and the onset of the main rupture of the 2005 West Off Fukuoka Prefecture earthquake Reviewed

    Hiroshi Takenaka, Takeshi Nakamura, Yosuke Yamamoto, Genti Toyokuni, Hiroshi Kawase

    Earth, Planets and Space   58 ( 1 )   75 - 80   2006

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    Near-source strong-motion records of the 2005 West Off Fukuoka Prefecture earthquake have two remarkable features. One is the presence of a relatively long period pulse with large amplitude on the fault-normal component of the velocity and displacement records, which is the result of the forward rupture directivity. The other is that the records show several seconds of small but increasing amplitude arrival (‘ initial rupture phase‘ ) followed by the onset of the main energy release (‘ main rupture phase‘ ). We first determined the precise geometry of the fault plane of this earthquake by examining the horizontal particle motion of the main S-wave portion on the records, as follows: the strike is N304°E, and the dip angle is 87°. The dip direction of the fault plane is northeast, and the surface intersection of the fault plane passes by the eastern coast of Genkai Island. We also obtained the relative location of the onset of the main rupture with respect to the hypocenter, and the mean rupture velocity between them. The distance between them is 5.1 km, the onset of the main rupture is located southeast above the hypocenter. The mean rupture velocity along the straight path is 1.4 km/s. It is found that the main rupture began 3.6 sec later from the origin time, at the central point between the hypocenter and Genkai Island. Our results suggest that Genkai Island directly suffered the strong effects of the forward rupture directivity during the earthquake. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)
    The Seismological Society of Japan
    The Volcanological Society of Japan
    The Geodetic Society of Japan
    The Japanese Society for Planetary Sciences
    TERRAPUB. © 2006, The Seismological Society of Japan, Society of Geomagnetism and Earth, Planetary and Space Sciences, The Volcanological Society of Japan, The Geodetic Society of Japan, The Japanese Society for Planetary Sciences. All rights reserved.

    DOI: 10.1186/BF03351917

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  • Fluid-Solid Boundary Implementation in the Velocity-Stress Finite-Difference Method Reviewed

    OKAMOTO Taro, TAKENAKA Hiroshi

    Zisin : Journal of the Seismological Society of Japan   57 ( 3 )   355 - 364   2005.2

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  • A Three-dimensionally Heterogeneous Structure Model for Seismic Wavefield Simulation in Northwestern Kagoshima Region Reviewed

    FUJII Yushiro, TAKENAKA Hiroshi, MIYAMACHI Hiroki

    Zisin : Journal of the Seismological Society of Japan   57 ( 3 )   365 - 375   2005.2

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  • An Efficient FDTD Solution for Seismic Plane-wave Responses of Vertically Heterogeneous Media Reviewed

    TANAKA Hiroki, TAKENAKA Hiroshi

    Zisin : Journal of the Seismological Society of Japan   57 ( 3 )   343 - 354   2005.2

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  • Influence of Anisotropy in the Fault Zone on the Seismic Waves Reviewed

    NAKAMURA Takeshi, TAKENAKA Hiroshi

    Zisin : Journal of the Seismological Society of Japan   57 ( 3 )   331 - 342   2005.2

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  • Strong S-wave anisotropy in the aftershock region of the 2000 Tottori-ken Seibu, Japan, earthquake (Mw6.6) Reviewed

    Takeshi Nakamura, Hiroshi Takenaka, Sadaomi Suzuki

    Earth, Planets and Space   57 ( 11 )   1055 - 1062   2005

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    The 2000 Tottori-ken Seibu earthquake (Mw6.6) occurred in Tottori prefecture, western Japan on October 6, 2000. We conducted aftershock observation and analyzed S-wave anisotropy using the aftershocks Mjma2.0 to 3.5 observed at two stations near the aftershock region. The fast S-waves are polarized to almost E-W direction, which corresponds to the P-axis direction of the mainshock. The delay time of the split S-waves ranges between 20 and 100 ms. The crack density inside and outside the aftershock area is estimated from the delay time. The distribution of crack density shows a strong spatial variation and depends on the ratio of the path length inside the aftershock region against the whole path length. Assuming a uniform distribution of anisotropy inside and outside the aftershock region, the crack densities inside and outside are 0.017 and 0.007, respectively. It thus seems probable that in the aftershock region the distribution of cracks is intensive and cracks are opened due to the presence of fluids in seismogenic layers. This considerable spatial variation of anisotropy between inside and outside the aftershock region suggests that the aftershock region may have different mechanical properties from the surrounding area. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS)
    The Seismological Society of Japan
    The Volcanological Society of Japan
    The Geodetic Society of Japan
    The Japanese Society for Planetary Sciences
    TERRAPUB.

    DOI: 10.1186/BF03351884

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  • Strong attenuation of shear waves in the focal region of the 1997 Northwestern Kagoshima earthquakes, Japan Reviewed

    Y Mamada, H Takenaka

    BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA   94 ( 2 )   464 - 478   2004.4

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    In 1997, two moderate earthquakes (M-JMA 6.5 on March 26 and MJMA 6.3 on May 13) occurred in northwestern Kagoshima prefecture, Japan. Using the records of aftershocks with focal depths from 5 to 10 km, recorded at a station located above the center of the aftershock zone, attenuation values for shear waves (Q(S)(-1)) were determined for the focal region. This region consists of the aftershock zones, including the rupture zones of the two mainshocks. A coda normalization method was applied for the measurement of Q(S)(-1) and determined as a function of frequency in five frequency bands centered at 1.5, 3, 6, 12, and 24 Hz. Before applying the method, a correction for the effect of the radiation pattern of shear waves on the spectral amplitude was made for frequency bands centered at 3 Hz and lower. Estimated Q(S)(-1)'s have significantly larger values compared to other previous studies in the crust. From our results, Q(S)(-1) can be approximately represented as a function of frequency f by Q(S)(-1)(f) = (9.93 X 10(-2))f(-0.95).
    In order to check the significance of the large values of Q(S)(-1) in the focal region, we also determined the attenuation in the surrounding area, using shear waves that propagate through both the focal region and the surrounding region. Our results show that the estimated Q(S)(-1) outside the focal region can be approximately represented as a function of frequency by Q(S)(-1)(f) = (1.03 X 10(-2))f(-0.59). This is similar to the crustal Q(S)(-1) in the surrounding area obtained by Kato (1999), suggesting that the values of Q(s)(-1) in the focal region are correctly estimated. Comparison of the values of Q(S)(-1) demonstrates that attenuation of S waves in the focal region is several times larger than in the surrounding area.

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  • Seismic structure of the crust and uppermost mantle in the incipient stage of back arc rifting - northernmost Okinawa Trough Reviewed

    Kazuo Nakahigashi, Masanao Shinohara, Sadaomi Suzuki, Ryota Hino, Hajime Shiobara, Hiroshi Takenaka, Minoru Nishino, Takeshi Sato, Shinji Yoneshima, Toshihiko Kanazawa

    Geophys. Res. Lett.   31 ( 2 )   n/a - n/a   2004.1

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    In 1999, a marine seismic structure survey was conducted in the northernmost Okinawa Trough. Outcrops of the acoustic basement through the sedimentary layers are seen in the obtained structures. Velocities of lower layer in upper crust are varying laterally from 5.7 to 6.2 km/s and thickness of 6.0-km/s layer ranges from 3 to 9 km. The lower crust has uniform thickness of about 15 km. The Pn velocity is 7.7-7.8 km/s and the total crustal thickness is about 25 km including sedimentary layers. The structure is in a first approximation similar to that of island arcs. However, the large heterogeneity of upper crust can be interpreted as a result of crustal thinning. The low Pn velocity and the outcrops of the acoustic basement relate to igneous activity in this area. These results suggest that the northernmost part of the Okinawa Trough is in the incipient stage of a back arc rifting.

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  • Near-source effect on radiation pattern of high-frequency S waves: strong SH-SV mixing observed from aftershocks of the 1997 Northwestern Kagoshima, Japan, earthquakes Reviewed

    H Takenaka, Y Mamada, H Futamure

    PHYSICS OF THE EARTH AND PLANETARY INTERIORS   137 ( 1-4 )   31 - 43   2003.5

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    It has been empirically recognized that high-frequency components of S waves radiated from earthquake do not show a radiation pattern predicted from a double-couple source, while the low frequency components show the standard double-couple radiation pattern. In this paper, we investigate this frequency dependence of radiation pattern using the high quality single-station records from the aftershock events of the 26 March 1997 and 13 May 1997 Northwestern Kagoshima, Japan, earthquakes. We focus on frequency dependence of energy partition between SH and SV waves in the direct S-phase. From the variation of the SH energy fraction with frequency we find that the energy fraction can be well predicted by theoretical radiation coefficients for a double-couple source at frequencies lower than 2 Hz, while at 3.5 Hz or higher it cannot be predicted and shows stochastic behavior. The intermediate frequencies can be seen as a transition from deterministic to stochastic. This supports the assumption that the radiation patterns of SH and SV waves are purely stochastic for high frequencies. Analyses of events which are located close to each other suggest that this stochastic nature is ascribed to strong SH and SV mixing or coupling induced by local structural effects near the sources. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0031-9201(03)00006-2

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  • Transition zone thickness beneath Indonesia as inferred using the receiver function method for data from the JISNET regional broadband seismic network Reviewed

    T Saita, D Suetsugu, T Ohtaki, H Takenaka, K Kanjo, Purwana, I

    GEOPHYSICAL RESEARCH LETTERS   29 ( 7 )   2002.4

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    [1] We analyzed broadband waveforms recorded by the newly deployed Japan-Indonesia Seismic Network to determine the depths of the 410 km and 660 km discontinuities and thickness of the mantle transition zone beneath Indonesia by the receiver function method. The discontinuities have an undulation with a maximum difference of 40 km with respect to the Iasp91 model. The thickness of the transition zone is well correlated with seismicity and seismic velocity anomalies, suggesting that the topography is caused by temperature anomalies associated with the subducted slabs beneath Indonesia.

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  • 不規則成層構造における地震波動場の理論的研究

    竹中博士

    北海道大学学位論文   1990

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  • 近地地震波の伝播に関する理論 Reviewed

    纐纈一起, 竹中博士

    地震. 2輯   42 ( 3 )   391 - 403   1989

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    DOI: 10.4294/zisin1948.42.3_391

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  • CMT解による観測点補正値を用いた沖縄本島南東沖の地震の震源再決定

    小松正直, 喜多村萌以, 竹中博士

    日本地震学会秋季大会講演予稿集(Web) 2022   S04-01   2022.10

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  • 海水層および海底地盤構造が海面地震動に与える影響の評価

    中村武史, 竹中博士

    日本地震学会秋季大会講演予稿集(Web) 2022   2022.10

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  • 東北地方太平洋沖地震震源域の波形トモグラフィー:分解能行列の検討

    岡元太郎, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集(Web) 2022   2022.10

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  • Estimation of subsurface motion from surface seismic records (2): improvement of the method based on the quantitative evaluation

    渡邉禎貢, 竹中博士, 小松正直, 大島光貴

    日本地球惑星科学連合大会予稿集(Web)   2022.5

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  • 地形を考慮した陸海統合3 次元地震波速度構造モデルを用いた大分県周辺の長周期地震動シミュレーション

    奥仲達也, 小松正直, 竹中博士, 吉見雅行, 中村武史, 岡元太郎

    岡山大学地球科学研究報告   28 ( 1 )   27 - 103   2022.3

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    DOI: 10.18926/ESR/63515

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  • 東北地方太平洋沖地震震源域の波形トモグラフィーに向けた波動場の検討

    岡元太郎, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集(Web) 2021   S01P-05   2021.10

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  • 水平成層構造での海面~海中における水中音響波形計算―海水層による増幅・減幅の影響評価-

    中村武史, 竹中博士

    日本地震学会秋季大会講演予稿集(Web) 2021   S01P-03   2021.10

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  • 2016年熊本地震で誘発された大分県中部の地震の初動読み取りと震源決定

    髙崎雄大, 小松正直, 渡邉禎貢, 竹中博士, 大島光貴

    日本地震学会秋季大会講演予稿集(Web) 2021   S19P-01   2021.10

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  • 地表観測記録を用いた地中地震動の推定:深い評価点における検討

    渡邉禎貢, 竹中博士, 小松正直, 大島光貴

    日本地球惑星科学連合大会予稿集(Web) 2021   2021.6

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  • Estimation of displacement waveforms by baseline correction of near-fault acceleration records of the 2016 Kumamoto earthquake with median filter

    Okayama University Earth Science Report   27 ( 1 )   39 - 50   2021.3

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    The 2016 Kumamoto earthquake sequence occurred on April 14 (MJMA 6.5) and April 16 (MJMA 7.3). Seismic intensity of 7 on the Japan Meteorological Agency (JMA) scale was observed in Mashiki Town, Kumamoto Prefecture for the both events and in Nishihara Village, Kumamoto Prefecture for the April-16 event. We estimate the displacement waveforms from these acceleration records. Since the acceleration seismograms include the long-period noise due to tilting of the ground and instrumental effects, the baseline corrections are required to derive the accurate velocity and displacement waveforms. We apply a median filter to the velocity waveforms to identify the linear trends on them due to the steplike noise on the acceleration records, and determine the time at which baseline shifts take place and the step value of each shift for the baseline correction through trial and error. Our baseline correction can successfully reconstruct the velocity and displacement waveforms from the acceleration records. The displacement waveforms show the static components consistent with the geodetic data.

    DOI: 10.18926/ESR/61959

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  • Synthetic nearfield seismograms at a subsurface position in a horizontally layered half-space

    Okayama University Earth Science Report   27 ( 1 )   29 - 38   2021.3

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    We extend the computational code of Takenaka and Sasatani (2000) for synthetic nearfield seismograms for horizontally layered elastic media, based on the reflection/transmission matrices and the discrete wavenumber summation method, to calculate seismic motion and its spatial derivatives at a subsurface position in the attenuative media. In this paper we describe the theory of this extension and show some numerical examples to verify the extended code.

    DOI: 10.18926/ESR/61956

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  • 北海道南西沖地震に伴う津波 : 小樽から礼文島まで (復刻 北海道南西沖地震と津波 : 2部 津波(1))

    後藤 章夫, 高橋 浩晃, 宇津木 充, 小野 忍, 西田 泰典, 大島 弘光, 笠原 稔, 竹中 博士, 斉田 智治

    月刊地球 = Chikyu monthly   42 ( 4 )   214 - 219   2020.4

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  • Theoretical analysis of the long-period velocity pulses observed in the 2016 Kumamoto Earthquake Sequence

    垂水洸太郎, 渡邉禎貢, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2020   2020

  • CMT solutions of earthquakes around Okinawa island from strong-motion records by using a land-ocean unified 3D structure model

    小松正直, 小割啓史, 渡邉禎貢, 岡元太郎, 中村武史, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2020   2020

  • Initial rupture process of the 2018 Hokkaido Eastern Iburi earthquake inferred from 2D/3D source imagings

    藤本怜, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2020   2020

  • Analytical solution of near-field term, intermediate term, far-filed term, and quasi-static displacement due to rectangular fault in a homogeneous whole space

    垂水洸太郎, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2020   2020

  • CMT solutions of the 2016 central Oita earthquakes using near-field strong motion records

    小割啓史, 小松正直, 竹中博士, 岡元太郎, 中村武史, 吉見雅行, 林田拓己

    日本地球惑星科学連合大会予稿集(Web)   2020   2020

  • Estimation of seismic motion at depth from records at a ground surface station without assumption of plane wave incidence

    渡邉禎貢, 竹中博士, 小松正直, 大島光貴, 中村武史

    日本地球惑星科学連合大会予稿集(Web)   2020   2020

  • Source process of the 14 April 2016 earthquake (M6.5) in Kumamoto area estimated by back-projection analysis

    大島光貴, 竹中博士, 松原誠

    日本地球惑星科学連合大会予稿集(Web)   2020   2020

  • Signal detection by amplitude distribution and Kullback-Leibler divergence

    大島光貴, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2020   2020

  • Early rupture process of the 2019 Off Yamagata earthquake

    藤本怜, 小割啓史, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2020   2020

  • Efficient New Schemes for Solving the 2D Dispersive Tsunami Equations

    ( 2 )   9 - 17   2020

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  • Computation of non-linear site response by the time-domain finite-difference method

    Okayama University Earth Science Report   26 ( 1 )   1 - 17   2019.12

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    We have developed a time-domain staggered-grid finite-difference code for modeling non-linear response of a one-dimensionally inhomogeneous subsurface structure to a SH plane-wave incidence. It employs the velocity-stress formulation of elastodynamic equation for the linear part, and adopts a elastoplastic rheology model for the non-linear relation between the stress and strain. In this paper, we apply this code to four constitutive models from linear-elastic to nonlinear: (1) linear elastic model, (2) linear viscoelastic model, (3) elastoplastic model, and (4) viscoelastoplastic model, which simulate shallow sand and clay structures and are vibrated by a vertically incident SH plane-wave of Ricker wavelet, to compare the linear and the non-linear soil behaviors including low strains damping (viscoelastic effect) and/or hysteretic attenuation (non-linear effect). We also apply it to a local strong-motion record of the 2000 Western-Tottori earthquake (MW6.8). We then simulate characteristics of non-linear site response such as reduction of the spectral amplitude in the high frequency band and shift of the peak frequencies to lower frequencies.

    DOI: 10.18926/ESR/58574

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  • 地震波形の振幅の確率密度関数を用いたP波・S波到着時刻の読み取りのための最適な階級数の検討

    大島光貴, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2019   2019

  • 平面波入射を仮定しないで,地表地震動から地中の入射波を算定する方法

    竹中博士, 小松正直, 渡邉禎貢, 大島光貴, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)   2019   2019

  • 3次元不均質構造モデルを用いた2016年大分県由布の誘発地震の余震のCMTインバージョン

    小割啓史, 小松正直, 竹中博士, 岡元太郎, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)   2019   2019

  • 岡山県全域の地盤構造の推定

    畝岡歩, 畝岡歩, 小松正直, 藤田高壮, 竹中博士, 西村敬一, 大島光貴, 川瀬博

    日本地震学会秋季大会講演予稿集(CD-ROM)   2019   2019

  • ソース・イメージング法を用いた2019年山形県沖の地震における初期段階の破壊過程の推定

    藤本怜, 小割啓史, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2019   2019

  • 南西諸島におけるP波・S波減衰構造

    小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2019   2019

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    日本地震学会秋季大会講演予稿集(CD-ROM)   2019   2019

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    日本地震工学シンポジウム論文集(CD-ROM)   15th   2018

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    小割啓史, 小松正直, 竹中博士, 岡元太郎, 中村武史

    日本地球惑星科学連合大会予稿集(Web)   2018   2018

  • 遠地津波のための線形分散波方程式を効率的に解く新しい方法

    秦真平, 竹中博士, 小松正直, 中村武史

    日本地球惑星科学連合大会予稿集(Web)   2018   2018

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    畝岡歩, 小松正直, 大島光貴, 竹中博士, 西村敬一, 川瀬博

    日本地球惑星科学連合大会予稿集(Web)   2018   2018

  • 南西諸島における震源スケーリング

    小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2018   2018

  • スペクトル・インバージョンに基づく岡山県内の強震観測点におけるサイト増幅特性

    畝岡歩, 小松正直, 竹中博士, 大島光貴, 西村敬一, 川瀬博

    日本地震学会秋季大会講演予稿集(CD-ROM)   2018   2018

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    竹中博士, 小松正直, 中村武史, 豊国源知, 岡元太郎

    日本地震学会秋季大会講演予稿集(CD-ROM)   2018   2018

  • 津波の非線形分散波方程式を効率的に解く新スキームの開発

    秦真平, 竹中博士, 小松正直, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)   2018   2018

  • 3次元理論地震波形計算によるグリーンランド氷床のQ値の推定

    豊国源知, 竹中博士, 小松正直, 高木涼太, 金尾政紀, 坪井誠司

    日本地震学会秋季大会講演予稿集(CD-ROM)   2018   2018

  • Exploration of S-wave velocity structure of Kita-Daito Island

    137   241 - 244   2017

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  • 地震波減衰トモグラフィから見る2016年熊本地震震源域下の流体分布

    竹中博士, 小松正直, 小田仁

    日本第四紀学会講演要旨集   47   2017

  • 2次元線形分散津波方程式の効率的な計算:スキーム編

    竹中博士, 秦真平, 小松正直, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)   2017   2017

  • 陸海統合3次元構造モデルにもとづく日本海溝の浅い地震のFAMT解析

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    日本地震学会秋季大会講演予稿集(CD-ROM)   2017   2017

  • S-wavevectorレシーバ関数解析による南西諸島の地震学的構造の推定

    村越匠, 竹中博士, 小松正直, 山田伸之

    日本地球惑星科学連合大会予稿集(Web)   2017   2017

  • 地震波干渉法を用いた別府湾周辺地域における深部地盤構造モデルの検証

    林田拓己, 吉見雅行, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2017   2017

  • 2016年熊本地震の強震記録を用いた岡山県内のサイト特性の評価

    畝岡歩, 小松正直, 竹中博士, 西村敬一

    日本地球惑星科学連合大会予稿集(Web)   2017   2017

  • アレイ解析による2016年4月16日大分誘発地震の震源の推定

    土井原健太, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2017   2017

  • 吐か喇(トカラ)列島中之島および宝島の深部地盤S波速度構造

    山田伸之, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2017   2017

  • 2次元線形分散津波方程式の効率的な計算:計算編

    秦真平, 竹中博士, 小松正直, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)   2017   2017

  • 南西諸島における連続地動記録を用いた雑微動の相互相関解析

    QIU Dongchen, 小松正直, 豊国源知, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2017   2017

  • バックプロジェクション法による2017年熊本地震の破壊過程の推定

    大島光貴, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2017   2017

  • 別府湾周辺における微動の連続観測記録を用いた深部地盤構造の検証

    林田拓己, 吉見雅行, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)   2017   2017

  • 強震動計算のための大分県域の3次元速度構造モデル

    吉見雅行, 松山尚典, 鈴木晴彦, 谷田貝淳, 林田拓己, 松島信一, 竹中博士, 三宅弘恵, 竹村恵二

    日本地球惑星科学連合大会予稿集(Web)   2017   2017

  • グリーンランド地殻浅部の経年的地震波速度変化

    豊国源知, 竹中博士, 高木涼太, 金尾政紀, 坪井誠司, 東野陽子

    日本地震学会秋季大会講演予稿集   2016   2016

  • 陸海統合3次元構造モデルにもとづく2016年薩摩半島西方沖地震のシミュレーション

    岡元太郎, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集   2016   2016

  • 南西諸島の広帯域地震波形データを用いたS-wavevectorレシーバ関数解析

    村越匠, 竹中博士, 小松正直, 山田伸之

    日本地震学会秋季大会講演予稿集   2016   2016

  • 焼きなまし法を用いた初動発震機構解の決定

    小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2016   2016

  • 南西諸島の広帯域地震波形データを用いたレシーバ関数解析

    村越匠, 竹中博士, 小松正直, 山田伸之

    日本地球惑星科学連合大会予稿集(Web)   2016   2016

  • 3次元及び2次元震源イメージングから推定した2014年伊予灘稍深発地震の初期段階の破壊過程

    宇佐美貴政, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2016   2016

  • 2015年大分県南部地震(Mj5.7)における大分県周辺の長周期地震動シミュレーションと地下構造モデルの検討

    奥仲達也, 小松正直, 竹中博士, 吉見雅行, 中村武史, 岡元太郎

    日本地球惑星科学連合大会予稿集(Web)   2016   2016

  • 2016年熊本地震震源域周辺の三次元地震波減衰構造

    小松正直, 小田仁, 竹中博士

    日本地震学会秋季大会講演予稿集   2016   2016

  • 2016年熊本地震初期破壊過程のイメージング

    宇佐美貴政, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集   2016   2016

  • 沖縄本島における深部地盤のS波速度構造

    山田伸之, 竹中博士, 小松正直

    物理探査学会学術講演会講演論文集   135th   2016

  • Application of simulated annealing to focal mechanism determination

    Okayama University Earth Science Report   22 ( 1 )   9 - 23   2015.12

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    Simulated annealing (SA) is known as one of the efficient methods for global optimization. It allows for getting an optimal solution by jumping out of local minimum. In this paper, we apply the simulated annealing to determination of focal mechanism solution. To investigate the feasibility of the application, we determine focal mechanism solution of the 14 March 2014 Iyo-Nada intermediatedepth earthquake. The computation of SA method is then 1278 times faster than that of the grid search method.

    DOI: 10.18926/ESR/54116

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  • Proposal of new seismic phases "Le" and "Re", generated by ice sheet

    37 ( 11 )   463 - 473   2015.11

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  • 大分平野における稠密小半径アレイ微動探査

    吉見雅行, 林田拓己, 松島信一, 川瀬博, 竹中博士, 山田伸之, 徳丸哲義, 杉山長志

    日本地震学会秋季大会講演予稿集   2015   2015

  • 沖縄島中部から奄美群島南部におけるS波速度構造探査

    山田伸之, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2015   2015

  • 紀伊半島周辺における陸上及び海底地すべりによる波動伝播シミュレーション

    中村武史, 竹中博士, 岡元太郎, 金田義行

    日本地球惑星科学連合大会予稿集(Web)   2015   2015

  • 2011年東北地方太平洋沖地震の不均質構造モデルを用いた破壊過程解析(5):相互相関係数による考察

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集   2015   2015

  • 八重山・宮古諸島島嶼部における深部地盤のS波速度構造~地下構造モデルの性能評価~

    山田伸之, 竹中博士

    日本地震学会秋季大会講演予稿集   2015   2015

  • グリーンランド氷床における広帯域連続地震波形記録を用いた地震波干渉法解析

    豊国源知, 竹中博士, 金尾政紀, 坪井誠司, 東野陽子

    日本地震学会秋季大会講演予稿集   2015   2015

  • 南海トラフ域における長周期地震動成分の伝播特性と震源メカニズム解析に与える影響の評価

    中村武史, 岡元太郎, 竹中博士

    日本地震学会秋季大会講演予稿集   2015   2015

  • 南西諸島における三次元地震波減衰トモグラフィ

    小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集   2015   2015

  • 2014年3月14日伊予灘稍深発地震の初期段階の破壊過程

    齋藤衛, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)   2015   2015

  • 南海トラフにおけるやや長周期地震動の観測とシミュレーションによる再現

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    日本地球惑星科学連合大会予稿集(Web)   2015   2015

  • 長大距離地震波動伝播シミュレーションのための地球の曲率を考慮した計算スキーム

    竹中博士, 豊国源知, 中村武史, 小松正直, 岡元太郎

    日本地球惑星科学連合大会予稿集(Web)   2015   2015

  • グリーンランド氷床モデルを用いた地震波伝播モデリング

    豊国源知, 竹中博士, 金尾政紀, 坪井誠司, 東野陽子

    日本地球惑星科学連合大会予稿集(Web)   2015   2015

  • Strong Motion Prediction for Large Inland Earthquakes

    49 ( 11 )   598 - 603   2014.11

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  • 地震波から推定される2011年東北地方太平洋沖地震の破壊過程:不均質構造モデルにもとづくグリーン関数を用いたインバージョン解析

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震工学シンポジウム論文集(CD-ROM)   14th   2014

  • 沖縄先島諸島におけるP波減衰構造

    小松正直, 竹中博士, 小田仁

    日本地震学会秋季大会講演予稿集   2014   2014

  • 不均質構造モデルによる地震波グリーン関数波形を用いた2011年東北地方太平洋沖地震の破壊過程(4)

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集   2014   2014

  • 八重山・宮古諸島島嶼部における深部地盤S波速度構造モデル

    山田伸之, 竹中博士

    日本地震学会秋季大会講演予稿集   2014   2014

  • 簡便なコーナ周波数fcの推定法と減衰量t*の決定

    小松正直, 竹中博士, 小田仁

    日本地震学会秋季大会講演予稿集   2014   2014

  • 月と火星の全球地震波伝播シミュレーション

    豊国 源知, 竹中 博士, 趙 大鵬, 石原 吉明

    SENAC : 東北大学大型計算機センター広報   46 ( 3 )   1 - 12   2013.7

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  • 基盤内S-wavevectorレシーバ関数を用いた九州下の地震学的構造の推定

    上田拓哉, 竹中博士, 村越匠

    物理探査学会学術講演会講演論文集   129th   2013

  • 桜島火山におけるACROSS震源位置で励起された弾性波の伝播シミュレーション

    竹中博士, 藤岡慧, 中村武史, 岡元太郎, 宮町宏樹, 八木原寛, 山岡耕春, 國友孝洋, 渡辺俊樹, 井口正人, 為栗健, 三ケ田均, 清水洋

    日本火山学会講演予稿集   2013   2013

  • 準円筒座標系2.5次元波動モデリング(3)-非弾性減衰-

    豊国源知, 竹中博士, 岡元太郎, ZHAO Dapeng

    日本地震学会秋季大会講演予稿集   2013   2013

  • 奄美大島でのS波速度構造探査-島の地震動評価のために-

    山田伸之, 竹中博士

    日本地震学会秋季大会講演予稿集   2013   2013

  • 3次元グリーンテンソル波形による2011年東北地方太平洋沖地震の破壊過程の推定(2):グリーンテンソル波形の違いの影響

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集   2013   2013

  • グリーンランド氷床上での地震波形観測に氷床が与える影響について

    豊国源知, 金尾政紀, 東野陽子, 姫野哲人, 坪井誠司, 竹中博士

    極域科学シンポジウム講演予稿集(CD-ROM)   4th   2013

  • S-wave velocity structure of Fukuoka area

    YAMADA Nobuyuki, TAKENAKA Hiroshi

    127   258 - 259   2012.11

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  • Global modeling of seismic wave propagation considering the effect by the Antarctic ice sheet

    34 ( 8 )   471 - 475   2012.8

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  • GPU-Accelerated Large-Scale Simulation of Seismic-Wave Propagation

    Tsubame ESJ. : e-science journal   6   11 - 16   2012.7

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  • ACROSSを用いた桜島における能動監視

    宮町宏樹, 八木原寛, 山岡耕春, 渡辺俊樹, 國友孝洋, 井口正人, 為栗健, 三ケ田均, 清水洋, 松島健, 竹中博士

    日本火山学会講演予稿集   2012   2012

  • 青い地球と白い大陸の地震学-固体地球振動特性と不均質構造・ダイナミクスの解明-南極氷床の効果を考慮した全地球地震波伝播モデリング

    豊国源知, 竹中博士, 金尾政紀

    月刊地球   34 ( 8 )   2012

  • 2011年東北地方太平洋沖地震の破壊過程解析のための3次元近地グリーンテンソル波形計算

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集   2012   2012

  • 南大東島における地盤震動調査-島の地震動評価のために-

    山田伸之, 立川真太郎, 竹中博士

    日本地震学会秋季大会講演予稿集   2012   2012

  • 地中観測網のS-wavevectorレシーバ関数で見る九州の地殻及び最上部マントルの地震学的構造

    上田拓哉, 村越匠, 竹中博士

    日本地震学会秋季大会講演予稿集   2012   2012

  • 近地地震における地震動・津波統合3次元数値シミュレーションの新スキーム

    竹中博士, 中村武史, 蔵本稔大, 岡元太郎, 豊国源知

    日本地震学会秋季大会講演予稿集   2012   2012

  • 海底地震観測網で観測された地震動の3次元波動伝幡シミュレーションによる再現-構造モデルにおける海水層の導入の重要性

    中村武史, 竹中博士, 岡元太郎, 金田義行

    日本地震学会秋季大会講演予稿集   2012   2012

  • 南西諸島における地震動シミュレーションのための三次元地下構造モデルの構築

    藤岡慧, 竹中博士, 山田伸之, 中村武史, 岡元太郎, 村越匠, 藤原広行

    日本地震学会秋季大会講演予稿集   2012   2012

  • 深井戸観測記録と深部地盤構造モデルを用いたS-wavevectorレシーバ関数解析による関東平野下のプレート構造の推定

    村越匠, 竹中博士

    日本地震学会秋季大会講演予稿集   2012   2012

  • モーメントテンソル点震源を用いた準円筒座標系2.5次元波動モデリング

    豊国源知, 竹中博士, 岡元太郎, ZHAO Dapeng, 伊藤喜宏, 長谷川昭

    日本地震学会秋季大会講演予稿集   2012   2012

  • 月表面地形・表層構造を考慮した月の地震波伝播モデリング

    岡元太郎, 小林直樹, 竹中博士

    日本惑星科学会秋季講演会予稿集(Web)   2011   2011

  • S-wavevectorレシーバ関数解析による関東平野のフィリピン海スラブ・太平洋スラブの形状

    村越匠, 竹中博士

    日本地震学会秋季大会講演予稿集   2011   2011

  • 2011年東北地方太平洋沖地震の破壊過程と近地全波形モデリング

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集   2011   2011

  • 時間領域差分法による地震波動としての近地地震津波の数値計算

    竹中博士, 藏本稔大, 中村武史, 岡元太郎, 豊国源知

    日本地震学会秋季大会講演予稿集   2011   2011

  • 全地球地震波伝播モデリングを用いた北極における地震波形記録の解釈

    豊国源知, 竹中博士, 金尾政紀

    極域科学・宙空圏・気水圏・生物・地学シンポジウム講演予稿集(CD-ROM)   2011   2011

  • アクロスによる桜島火山のマグマ移動検出に向けた能動的アプローチ

    宮町宏樹, 井口正人, 山岡耕春, 渡辺俊樹, 八木原寛, 為栗健, 三ケ田均, 竹中博士, 清水洋

    日本火山学会講演予稿集   2011   2011

  • 喜界島における微動探査-島の地震動評価のために-

    山田伸之, 竹中博士, 奥平良太

    日本地震学会秋季大会講演予稿集   2011   2011

  • 筑紫平野北東部における微動アレイ探査

    奥平良太, 竹中博士, 山田伸之

    日本地震学会秋季大会講演予稿集   2011   2011

  • 2011年駿河湾で起こった地震における初期段階の震源過程

    後藤史紀, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集   2011   2011

  • Incorporation of anelastic attenuation effects in synthetic seismograms for transversely isotropic media

    TAKENAKA Hiroshi, NAKAMURA Takeshi

    Geophysical bulletin of Hokkaido University   ( 73 )   185 - 194   2010.3

  • 自己重力の効果を考慮した球座標系2.5次元地震波伝播モデリング(1):カウリング近似

    豊国源知, 竹中博士

    日本地震学会秋季大会講演予稿集   2010   2010

  • GPUを用いた地震波伝播シミュレーション(3):地形・流体層と非弾性減衰効果の導入

    岡元太郎, 竹中博士, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集   2010   2010

  • レシーバー関数解析のための深井戸観測記録の料理法

    竹中博士, 村越匠

    日本地震学会秋季大会講演予稿集   2010   2010

  • 先島諸島におけるS波速度構造探査

    山田伸之, 竹中博士, 奥平良太, 後藤史紀, 蔵本稔大

    日本地震学会秋季大会講演予稿集   2010   2010

  • 福岡県震度計観測点におけるサイト増幅特性の抽出

    大島光貴, 竹中博士, 川瀬博

    日本地震工学シンポジウム論文集(CD-ROM)   13th   2010

  • 自己重力を考慮した全地球地震波動場の計算と極域波形データの比較

    豊国源知, 竹中博士, 金尾政紀

    極域科学・宙空圏・気水圏・生物・地学シンポジウム講演予稿集(CD-ROM)   2010   2010

  • 陸上地形・海底地形を考慮した3次元差分法による長周期地震動シミュレーション

    竹中博士, 中村武史, 岡元太郎, 金田義行

    日本地震工学シンポジウム論文集(CD-ROM)   13th   2010

  • GPUによる地震波伝播シミュレーション

    岡元太郎, 竹中博士, 中村武史

    情報処理学会シンポジウム論文集   2010 ( 5 )   2010

  • 2009年8月11日駿河湾で発生した地震の3次元HOT-FDMによる波動伝播シミュレーション

    中村武史, 竹中博士, 岡元太郎, 金田義行

    日本地震学会秋季大会講演予稿集   2009   2009

  • GPGPUを用いた地震波伝播計算の試み

    岡元太郎, 竹中博士

    日本地震学会秋季大会講演予稿集   2009   2009

  • 3次元不均質構造における平面波斜め入射問題を解く新しい方法:支配方程式と差分法による解法

    竹中博士, 岡元太郎, 中村武史

    日本地震学会秋季大会講演予稿集   2009   2009

  • 地球中心も含めた精度と効率のよい全地球地震波伝播モデリング

    豊国源知, 竹中博士

    日本地震学会秋季大会講演予稿集   2009   2009

  • 海底火山活動に伴って発生する地震波動の海域伝播シミュレーションに有効な差分コードの開発

    竹中博士, 中村武史, 金田義行

    日本火山学会講演予稿集   2008   2008

  • 2008年岩手・宮城内陸地震における開始5秒間の破壊過程のイメージング

    竹中博士, 山本容維

    日本地震学会秋季大会講演予稿集   2008   2008

  • 2005年福岡県西方沖地震における高精度すべり時空間分布の推定とその検証

    大島光貴, 竹中博士

    日本地震工学会大会梗概集   6th   2008

  • 近地P波記録のイメージングから得られた2008年岩手・宮城内陸地震における最初の5秒間の震源過程

    竹中博士, 山本容維

    日本地震工学会大会梗概集   6th   2008

  • 鉛直方向不均質粘弾性媒質におけるtau-p領域の波動方程式と時間領域差分法計算

    竹中博士, JAFARGANDOMI Arash

    物理探査学会学術講演会講演論文集   117th   2007

  • 近地P波記録から推定した2007年能登半島地震の第2震源・初期破壊・主破壊とアスペリティ

    山本容維, 竹中博士

    日本地震学会秋季大会講演予稿集   2007   2007

  • 近地P波記録のバックプロジェクションによるアスペリティー分布の推定:リアルタイム・イメージングに向けた検討

    竹中博士, 山本容維

    日本地震学会秋季大会講演予稿集   2007   2007

  • 標準地球モデルのための解析的な実効差分格子パラメータの計算

    豊国源知, 竹中博士

    日本地震学会秋季大会講演予稿集   2007   2007

  • 2007年新潟県中越沖地震における初期破壊・主破壊・アスペリティー:柏崎における大震動との関係

    山崎寛一, 山本容維, 竹中博士

    日本地震学会秋季大会講演予稿集   2007   2007

  • 近地P波記録から推定した新潟県中越沖地震の震源過程:最初の5秒間と強震動生成

    竹中博士, 山崎寛一, 山本容維

    日本地震工学会大会梗概集   5th   2007

  • 近地P波記録から推定した能登半島地震の震源過程:最初の5秒間と強震動生成

    山本容維, 竹中博士

    日本地震工学会大会梗概集   5th   2007

  • 福岡県西方沖地震における強震動記録と地盤増幅効果

    栗林健太郎, 竹中博士, 川瀬博

    日本建築学会学術講演梗概集B-2 構造2   2007   2007

  • 地球深部を伝播する地震波の効率的モデリング--準球座標系アプローチ (フロンティア地震学の最前線)

    豊国 源知, 竹中 博士

    月刊地球   28 ( 9 )   607 - 611   2006.9

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  • 準球座標系差分法(5)

    豊国源知, 竹中博士, WANG Yanbin

    日本地震学会秋季大会講演予稿集   2006   2006

  • アスペリティを考慮したStochastic finite-fault modelingによる2005年福岡県西方沖地震の強震動の再現

    大島光貴, SAYED Moustafa, 竹中博士, 川瀬博

    日本地震学会秋季大会講演予稿集   2006   2006

  • P波を用いたアスペリティーのリアルタイム・イメージング:リアルタイム強震動予測/推定へ向けて

    竹中博士, 山本容維

    日本地震学会秋季大会講演予稿集   2006   2006

  • ジャワ海溝の微細地殻構造モデルと2.5次元差分法を用いた2006年7月17日ジャワ島沖地震の震源過程解析

    岡元太郎, 竹中博士

    日本地震学会秋季大会講演予稿集   2006   2006

  • 2.5次元差分法で探る2005年宮城県沖の地震の震源過程

    岡元太郎, 竹中博士

    日本地震学会秋季大会講演予稿集   2005   2005

  • 準球座標系差分法(4)

    豊国源知, 竹中博士, WANG Yanbin

    日本地震学会秋季大会講演予稿集   2005   2005

  • 断層帯周辺における異方性速度構造推定のための地震波動場の計算:茂住-祐延断層における適用

    中村武史, 竹中博士, 西上欽也

    日本地震学会秋季大会講演予稿集   2005   2005

  • 遠地地震波形記録の平面波近似による九州地方直下におけるモホ面イメージング

    大財綾子, 竹中博士, 村越匠

    日本地震学会秋季大会講演予稿集   2005   2005

  • (3)地震動予測地図作成手法の研究及び強震動・震災被害予測システムの開発((3)地震による被害軽減に資する地震調査研究の推進, 1プロジェクト研究)

    藤原 広行, 青井 真, 河合 伸一, 功刀 卓, 森川 信之, 本多 亮, 小林 京子, 大井 昌弘, 八十島 裕, 先名 重樹, 神野 達夫, 石井 透, 奥村 俊彦, 早川 譲, 渡辺 基史, 福島 美光, 竹中 博士, 水谷 守, 篠塚 正宣, 久田 嘉章, 市村 強

    防災科学技術研究所年報   15   "I - 20"-"I-22"   2004.9

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    地震調査研究推進本部地震調査委員会による地震動予測地図作成に資するため、各種地震計による観測網からのデータを最大限に活用し、ある一定期間内にある地域が強い地震動に襲われる確率を予測した確率論的地震動予測地図や、特定の断層を想定し、それが活動した場合をモデル化して震源断層周辺域の地盤の揺れの分布を予測したシナリオ地震による地震動予測地図を作成する。また、高精度の強震動予測を行い、地震のメカニズムや断層面などを推定するとともに、断層面上での詳細な破壊過程を分析する。さらに、地震災害を引き起こす強震動を予測し、震災被害予測を行う。これらの成果は、地震調査研究推進本部委員会において進めている「全国を概観した地震動予測地図」の作成(平成16年末を目途)に活用されている。

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  • Research Report of the Crust and Upper Mantle Structure in the Okinawa Trough, off West Kyushu by Using Ocean Bottom Seismometer

    Science reports, Department of Earth and Planetary Sciences, Kyushu University   21 ( 3 )   69 - 107   2004.1

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    The Okinawa Trough is located in the・ back-arc region of the Ryukyu Island arc, and is considered to be an active spreading area. In fall of 1999, seismic survey using ocean bottom seismometers was conducted to obtain the detailed seismic structure in the northernmost part of the Okinawa Trough. The total crust thickness is 25 km including a sedimentary layer. The velocity of the upper crust changes from 5.7-6.0 km/s in the upper part to 6.1-6.2 km/s in the lower part. And its thickness changes from 3 km to 9 km. The lower crust of which velocity slightly changes from 6.5-6.7 km/sin the upper part to 6.8-6.9 km/sin the lower part has uniform thickness of about 15 km. The Pn velocity is determined to be 7.7-7.8 km/s. The seismic structure suggests that the northernmost part of the Okinawa Trough is in the incipient stage of a backarc rifting.

    DOI: 10.15017/4493142

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  • レシーバ関数解析によるインドネシアの地殻構造の推定

    村越匠, 竹中博士

    日本地震学会秋季大会講演予稿集   2004   2004

  • 準球座標系差分法 (2)

    豊国源知, 竹中博士, WANG Y

    日本地震学会秋季大会講演予稿集   2004   2004

  • 時間・空間的に連続なすべり速度関数を用いた1997年鹿児島県北西部地震の強震動シミュレーション

    藤井雄士郎, 竹中博士

    日本地震学会秋季大会講演予稿集   2004   2004

  • レシーバ関数インバージョンによって推定した松代直下の地殻及び最上部マントルのS波速度構造

    安藤利彦, 竹中博士, 村越匠, 高山博之, 小河原隆広, 仲底克彦

    日本地震学会秋季大会講演予稿集   2003   2003

  • グリッドモデルを用いた運動学的震源インバージョン

    竹中博士, 藤井雄士郎

    日本地震学会秋季大会講演予稿集   2003   2003

  • 人工地震探査のための準円筒座標系2.5次元波動モデリング

    竹中博士, 田中宏樹, 岡元太郎, KENNETT B L N

    日本地震学会秋季大会講演予稿集   2003   2003

  • (42) 地震素過程と地球内部構造の解明に関する総合的研究(5 共同研究,I 研究活動)

    石田 瑞穂, 井上 公, 堀 貞喜, 関口 渉次, 福山 英一, 笠原 稔, 勝俣 啓, 石井 紘, 佃 為成, 橋本 信一, 渡辺 茂, 山田 功, 山岡 耕春, 山内 常生, 山田 守, 宮島 力男, 奥田 隆, 根元 謙次, 田中 寅夫, 渡辺 晃, 平原 和朗, 許斐 直, 澁谷 拓郎, 鈴木 貞臣, 竹中 博士, 清水 洋, 角田 寿喜, 後藤 和彦, 平野 舟一郎, 宮町 宏樹

    防災科学技術研究所年報   13   150 - 150   2002.10

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  • (6) 強震動・震災被害予測システムに関する研究(1 プロジェクト研究,I 研究活動)

    藤原 広行, 河合 伸一, 青井 真, 功刀 卓, 神野 達夫, 森川 信之, 小林 京子, 竹中 博士, 久田 嘉章

    防災科学技術研究所年報   13   20 - 21   2002.10

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  • Estimation of coda-wave attenuation in the vicinity of metropolitan Cairo, Egypt (共著)

    MOUSTAFA Sayed S.R., TAKENAKA Hirohsi, MAMADA Yutaka

    Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth Planet. Sci.   31(2), 71-79 ( 2 )   71 - 79   2002

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  • Source process of the largest aftershock (M5.5) of the 1997 Kagoshima earthquakes, Kyushu, Japan (共著)

    Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth Planet. Sci.   31(2), 59-70   2002

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  • 3-D finite-difference simulation of seismic fault zone waves - Application to the fault zone structure of the Mozumi-Sukenobu fault, central Japan

    Y Mamada, Y Kuwahara, H Ito, H Takenaka

    EARTH PLANETS AND SPACE   54 ( 11 )   1055 - 1058   2002

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    Fault zone waves have the potential to be a powerful tool to reveal the fine structure of a fault zone down to the seismogenic depth. Seismic fault zone waves include head waves, trapped waves and direct body waves propagating in the fault zone. 3-D numerical simulation is necessary to interpret the waveforms in the presence of low-velocity zones with relatively complex fault structure. We computed finite difference (FD) synthetic seismograms to fit the seismograms of explosions, which contain frequencies up to 25 Hz, recorded by a linear seismometer array across the Mozumi-Sukenobu fault, central Japan. We find fault zone head waves, direct P waves propagating within the low-velocity zone and wave trains following the direct P waves associated with the fault for both observed and synthetic waveforms. Thus, modelling of fault zone waves is expected to determine details of complex fault zone structure.

    DOI: 10.5636/eps.54.11_1055

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  • Estimation of Coda-Wave Attenuation in the Vicinity of Metropolitan Cairo, Egypt

    MOUSTAFA Sayed S.R., TAKENAKA Hirohsi, MAMADA Yutaka

    Memoirs of the Faculty of Science, Kyushu University. Series D, Earth and planetary sciences   31(2), 71-79 ( 2 )   71 - 79   2002

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  • MPIを用いた時間領域差分法による3次元地震波動場の並列計算(共著)

    竹中博士

    九州大学情報基盤センター広報   2 ( 1 )   85 - 94   2002

  • 2000年鳥取県西部地震の震源域における余震観測(共著)

    九州大学大学院理学研究院研究報告(地球惑星科学)   21(2), 49-59   2002

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  • Source Process of the Largest Aftershock (M5.5) of the 1997 Northwestern Kagoshima Earthquakes, Kyushu, Japan

    FUJII Yushiro, TAKENAKA Hiroshi

    Memoirs of the Faculty of Science, Kyushu University. Series D, Earth and planetary sciences   31(2), 59-70 ( 2 )   59 - 70   2002

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  • 地震波散乱問題における積分方程式のウエーブレットを用いた解法の検討:大規模積分作用素行列の圧縮(共著)

    竹中 博士, 藤原 広行

    九州大学大学院理学研究院研究報告(地球惑星科学)   21(2), 61-68 ( 2 )   61 - 66   2002

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  • 3-D finite-difference simulation of seismic fault zone waves - Application to the fault zone structure of the Mozumi-Sukenobu fault, central Japan

    Y Mamada, Y Kuwahara, H Ito, H Takenaka

    EARTH PLANETS AND SPACE   54 ( 11 )   1055 - 1058   2002

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    Fault zone waves have the potential to be a powerful tool to reveal the fine structure of a fault zone down to the seismogenic depth. Seismic fault zone waves include head waves, trapped waves and direct body waves propagating in the fault zone. 3-D numerical simulation is necessary to interpret the waveforms in the presence of low-velocity zones with relatively complex fault structure. We computed finite difference (FD) synthetic seismograms to fit the seismograms of explosions, which contain frequencies up to 25 Hz, recorded by a linear seismometer array across the Mozumi-Sukenobu fault, central Japan. We find fault zone head waves, direct P waves propagating within the low-velocity zone and wave trains following the direct P waves associated with the fault for both observed and synthetic waveforms. Thus, modelling of fault zone waves is expected to determine details of complex fault zone structure.

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  • 従来の震源インバージョンの結果から時間空間的に連続なすべり時間関数を抽出する方法

    竹中博士, 藤井雄士郎, 川瀬博, 宮腰研, 岩田知孝

    日本地震学会秋季大会講演予稿集   2002   2002

  • 2000年鳥取県西部地震の断層直上アレーで観測されたS波偏向異方性

    中村武史, 安藤利彦, 田中宏樹, 竹中博士, 桑原保人, 侭田豊, 今西和俊

    日本地震学会秋季大会講演予稿集   2002   2002

  • 2000年鳥取県西部地震の震源域におけるS波偏向異方性 (2)

    中村武史, 竹中博士, 鈴木貞臣

    日本地震学会秋季大会講演予稿集   2002   2002

  • A multidomain approach of the Fourier pseudospectral method using discontinuous grid for elastic wave modeling

    YB Wang, H Takenaka

    EARTH PLANETS AND SPACE   53 ( 3 )   149 - 158   2001

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    Pseudospectral method is an efficient and high-accuracy numerical modeling technique that has been applied to the simulation of seismic wavefields in realistic models with complex structures such as sedimentary basin. However, if the sedimentary layers are included in the model, high velocity contrasts arise because of the very low S-wave velocities of the sediments as compared with the bedrock. The grid spacing then has to be very small, which leads to spatial oversampling in regions with higher velocities. As a result, we also have to use very small time interval for time marching, so that the computation requires much CPU time. A treatment of this problem is use of a multidomain approach that can employ different grid spacings in different regions, i.e. "discontinuous grid". In this study, we propose a scheme for the Fourier pseudospectral method using discontinuous grid, which uses an interpolation by the FFT. This scheme can reduce the computation time and the required computer memory as compared with the conventional one. The accuracy and efficiency of this approach are demonstrated in the present paper through examples of 2-D elastic wave modeling.

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  • Small scale heterogeneities in the focal region of the 1997 northwestern Kagoshima earthquakes, Japan(共著)

    Proceedings of the 5th SEGJ International Symposium   147-151   2001

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  • Modelling seismic wave propagation in a two-dimensional cylindrical whole-earth model using the pseudospectral method

    Yanbin Wang, Hiroshi Takenaka, Takashi Furumura

    Geophysical Journal International   145 ( 3 )   689 - 708   2001

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    We present a method for modelling seismic wave propagation in a whole-earth model by solving the elastodynamic equations in 2-D cylindrical coordinates (r, 0) using the Fourier pseudospectral method (PSM). In solving the 2-D cylindrical elastodynamic equations for a whole-earth model, a singularity arises at the centre (r = 0) of the earth. To avoid the singularity, we develop a scheme that uses extension of field variables in the radial direction, with which computation of the wavefield at the centre is avoided, so that the wave propagation through the centre can be calculated. The time interval used in the calculation is determined by the smallest lateral grid spacing around the centre in the model. In a cylindrical coordinate system, the smallest lateral grid spacing is generally so small that the calculation is too time-consuming to be realistically carried out even on a supercomputer. We adopt a multidomain scheme to increase the smallest lateral grid spacing and avoid the oversampling of the physical domain around the centre of the earth. A smoothing scheme in the wavenumber domain is also proposed, which enables us to use a large enough time interval to allow the calculation for the whole-earth model on a desktop workstation. The waveforms calculated by the present method are compared with those obtained by the Direct Solution Method (DSM) to demonstrate their high accuracy. This method significantly reduces the computer memory and computation time required and makes it possible to study the effects of small-wavelength heterogeneities that can be approximated as azimuthally symmetric on wave propagation in the earth. We apply the present method to study the effects of local heterogeneity in the earth by adding a low-velocity perturbation above the core-mantle boundary (CMB) to the IASP91 earth model.

    DOI: 10.1046/j.1365-246X.2001.01413.x

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  • A multidomain approach of the Fourier pseudospectral method using discontinuous grid for elastic wave modeling

    YB Wang, H Takenaka

    EARTH PLANETS AND SPACE   53 ( 3 )   149 - 158   2001

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    Pseudospectral method is an efficient and high-accuracy numerical modeling technique that has been applied to the simulation of seismic wavefields in realistic models with complex structures such as sedimentary basin. However, if the sedimentary layers are included in the model, high velocity contrasts arise because of the very low S-wave velocities of the sediments as compared with the bedrock. The grid spacing then has to be very small, which leads to spatial oversampling in regions with higher velocities. As a result, we also have to use very small time interval for time marching, so that the computation requires much CPU time. A treatment of this problem is use of a multidomain approach that can employ different grid spacings in different regions, i.e. "discontinuous grid". In this study, we propose a scheme for the Fourier pseudospectral method using discontinuous grid, which uses an interpolation by the FFT. This scheme can reduce the computation time and the required computer memory as compared with the conventional one. The accuracy and efficiency of this approach are demonstrated in the present paper through examples of 2-D elastic wave modeling.

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  • Small scale heterogeneities in the focal region of the 1997 northwestern Kagoshima earthquakes, Japan(共著)

    Proceedings of the 5th SEGJ International Symposium   147-151   2001

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  • 太平洋西縁沈み込み帯のマントル遷移層構造(共著)

    大滝 壽樹, 斉田 智治, 末次 大輔

    月刊地球   23(27), 455-458 ( 7 )   455 - 458   2001

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  • Installation Experiment of Broadband Seismometers in Shallow Vaults

    YOSHIDA Yasuhiro, KANJO Kenji, HARADA Satoshi, FUJIWARA Kenji, OHTAKI Toshiki, TANAKA Akiko, KANESHIMA Satoshi, SUETSUGU Daisuke, KAMIYA Shin'cihiro, ISHIHARA Yasushi, TAKENAKA Hiroshi, SAITA Tomoharu, FUJII Yushiro

    Zisin (Journal of the Seismological Society of Japan. 2nd ser.)   54, 9-16 ( 1 )   9 - 16   2001

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    The needs for installing broadband seismometers in inconvenient places are increasing. A simple and easy installation method is necessary for this purpose because it is difficult to make seismic observatory consuming much time and money. However only a few researches have been done for this purpose. In this paper we try to find the best way to install seismometers in inconvenient places. To decrease background noises under simple installation, we tested several ways to install broadband seismometers in shallow vaults. We made two vaults with concrete blocks whose sizes are about 1.5m3 and install a broadband seismometer in it. One block was set on the ground, and the other was settled below the ground. We checked background noise level of vertical component for three cases of insulation stuff: sand, styrofoam, and none. The noise level of the seismometers below the ground is lower than that on the ground for all three cases. The noise level is the lowest when the seismometer is installed in the underground vault filled with sand. The order of the amplitude of noise level is in proportion to the temperature fluctuation near the seismometer. Noise levels show higher correlation with temperature than wind speed, precipitation and atmospheric pressure. These suggest that the inhibition of temperature change near seismometers is the key to decrease background noise level. Therefore the installation of seismometer in the underground vault filled with sand achieves the lowest noise level, though the level is about 10dB higher than that in deep tunnel at permanent observatory near the vault.

    DOI: 10.4294/zisin1948.54.1_9

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  • Modelling seismic wave propagation in a two-dimensional cylindrical whole-earth model using the pseudospectral method

    Yanbin Wang, Hiroshi Takenaka, Takashi Furumura

    Geophysical Journal International   145 ( 3 )   689 - 708   2001

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    We present a method for modelling seismic wave propagation in a whole-earth model by solving the elastodynamic equations in 2-D cylindrical coordinates (r, 0) using the Fourier pseudospectral method (PSM). In solving the 2-D cylindrical elastodynamic equations for a whole-earth model, a singularity arises at the centre (r = 0) of the earth. To avoid the singularity, we develop a scheme that uses extension of field variables in the radial direction, with which computation of the wavefield at the centre is avoided, so that the wave propagation through the centre can be calculated. The time interval used in the calculation is determined by the smallest lateral grid spacing around the centre in the model. In a cylindrical coordinate system, the smallest lateral grid spacing is generally so small that the calculation is too time-consuming to be realistically carried out even on a supercomputer. We adopt a multidomain scheme to increase the smallest lateral grid spacing and avoid the oversampling of the physical domain around the centre of the earth. A smoothing scheme in the wavenumber domain is also proposed, which enables us to use a large enough time interval to allow the calculation for the whole-earth model on a desktop workstation. The waveforms calculated by the present method are compared with those obtained by the Direct Solution Method (DSM) to demonstrate their high accuracy. This method significantly reduces the computer memory and computation time required and makes it possible to study the effects of small-wavelength heterogeneities that can be approximated as azimuthally symmetric on wave propagation in the earth. We apply the present method to study the effects of local heterogeneity in the earth by adding a low-velocity perturbation above the core-mantle boundary (CMB) to the IASP91 earth model.

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  • レシーバ関数インバージョンによる九州の地殻構造の推定

    村越匠, 竹中博士

    日本地震学会秋季大会講演予稿集   2001   2001

  • 3次元差分法による断層トラップ波のシミュレーション 茂住祐延断層への適用

    侭田豊, 桑原保人, 伊藤久男, 竹中博士

    日本地震学会秋季大会講演予稿集   2001   2001

  • Tomographic low-velocity anomalies in the uppermost mantle around the northeastern edge of Okinawa trough, the backarc of Kyushu

    H Sadeghi, S Suzuki, H Takenaka

    GEOPHYSICAL RESEARCH LETTERS   27 ( 2 )   277 - 280   2000.1

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    A simultaneous inversion for three-dimensional velocity structure and hypocentral parameters is used to determine the tomographic images of the backarc of Kyushu, southwestern Japan. The data used in the imaging are the first arrival times of 2736 local earthquakes recorded at 305 stations in a wide region from western Japan to eastern China. Additional data are provided by including arrival times of 357 teleseismic earthquakes. We got the high resolution of the uppermost mantle images for P waves at least in the depth range to 150 km, the latitude range of 30 degrees-34 degrees N and the longitude range of 128 degrees-132 degrees E. Results of inversion reveal a major zone of strong low velocity under west off Kyushu Island in the depth from 40 km to 100 km. This feature may result from partially melting in relation to the upwelling of hot mantle around the northeastern edge of the extending Okinawa trough.

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  • Tomographic low-velocity anomalies in the uppermost mantle around the northeastern edge of Okinawa trough, the backarc of Kyushu

    H Sadeghi, S Suzuki, H Takenaka

    GEOPHYSICAL RESEARCH LETTERS   27 ( 2 )   277 - 280   2000.1

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    Language:English   Publisher:AMER GEOPHYSICAL UNION  

    A simultaneous inversion for three-dimensional velocity structure and hypocentral parameters is used to determine the tomographic images of the backarc of Kyushu, southwestern Japan. The data used in the imaging are the first arrival times of 2736 local earthquakes recorded at 305 stations in a wide region from western Japan to eastern China. Additional data are provided by including arrival times of 357 teleseismic earthquakes. We got the high resolution of the uppermost mantle images for P waves at least in the depth range to 150 km, the latitude range of 30 degrees-34 degrees N and the longitude range of 128 degrees-132 degrees E. Results of inversion reveal a major zone of strong low velocity under west off Kyushu Island in the depth from 40 km to 100 km. This feature may result from partially melting in relation to the upwelling of hot mantle around the northeastern edge of the extending Okinawa trough.

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  • An imaging technique for subsurface faults using Teleseismic-Wave Records II - Improvement in the detectability of subsurface faults

    T Murakoshi, H Takenaka, D Suetsugu

    EARTH PLANETS AND SPACE   52 ( 1 )   3 - 11   2000

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    We have developed an imaging algorithm for subsurface faults on the basis of the steepest descent method in our previous paper. In this paper we introduce two new techniques, the multi-event stacking and multi-master stacking, to improve detectability for subsurface faults. The multi-event stacking is a technique using data from plural earthquakes with different incident angles. The multi-master stacking is a technique using data of a single earthquake, in which the images obtained by employing different master receiver are stacked. We examined the feasibility of our approach using several trial models and synthetic data with different signal to noise ratios, different pulse durations and different incident angles in the two dimensional SH cases. In the numerical experiments, we could recover the image of the subsurface fault for all the trial models used, which indicates our method has a potential for sensing real subsurface faults.

    DOI: 10.5636/eps.52.3

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  • A Hybrid PSM/FDM parallel simulation for large-scale 3-D seismic (acustic) wavefield

    FURUMURA Takashi, KOKETSU Kazuki, TAKENAKA Hiroshi

    Geophysical exploration   53 ( 4 )   294 - 308   2000

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  • Numerical experiments for seismic tomography using the Singular Value Decomposition (SVD) technique(共著)

    21 ( 1 )   9 - 18   2000

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  • 特異値分解法を用いたサイスミック・トモグラフィの検討(共著)

    中村 めぐみ, 林田 智宏, 竹中 博士

    九州大学大学院研究報告, 地球惑星科学   21 ( 1 )   9 - 18   2000

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  • Seismograph Orientation at K-NET Observatories (2): Oita Prefecture

    WATANABE Atsushi, TAKENAKA Hiroshi, FUJII Yushiro, FUJIWARA Hiroyuki

    Zisin (Journal of the Seismological Society of Japan. 2nd ser.)   53 ( 2 )   185 - 192   2000

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    DOI: 10.4294/zisin1948.53.2_185

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  • A scheme for estimating the location and tangential plane of a reflector

    H Takenaka

    EARTH PLANETS AND SPACE   52 ( 4 )   299 - 303   2000

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    Magmatic reflectors have been detected beneath some volcanic regions by analysing some reflection phases of seismograms. In this letter we consider a problem to determine the location and tangential plane of such a reflector from the ray parameter, back-azimuth and travel time of a reflection phase, and present a scheme to solve it. It is then shown that the problem is essentially a one-dimensional root-finding problem whose independent variable is only the depth of the reflection point, and thus it can be solved by a line search method such as the one-dimensional grid search. While homogeneous velocity structure models have been used in the conventional analyses, the present scheme employs a vertically inhomogeneous one and can also easily treat converted phases at the reflector.

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  • Effect of vertical velocity gradient on ground motion in a sediment-filled basin due to incident SV wave

    YB Wang, H Takenaka, T Furumura

    EARTH PLANETS AND SPACE   52 ( 1 )   13 - 24   2000

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    The natural sedimental deposits in basins show strong vertical heterogeneity in their material parameters. The aim of this paper is to investigate the effects of such vertical heterogeneity, especially vertical velocity gradient, inside basin on the seismic ground motion through the parametric study on the response of a two-dimensional semi-cylindrical sediment-filled basin to a vertical incidence of plane SV wave using the pseudospectral method. This numerical study has tried to find the effects caused by vertical velocity gradient through the use of synthetic seismograms, wavefield snapshots and surface amplitude distribution. Simulation results clearly demonstrate the derailed character of wave propagation phenomena in basins with vertical velocity gradient, which produces characteristic amplification pattern of the surface motion caused mainly by the generation of strong Rayleigh wave induced at the basin edge associated with large lateral velocity change across the basin edge. Amplification pattern at the surface strongly depends on both the vertical velocity gradient in the basin and the predominant frequency of the incident wave. Although similar phenomena on wave propagation and surface motion found in previous studies for homogeneous basin models have also been observed in this study, it has been found that the vertical velocity gradient enhances such phenomena. The results suggest that it is important to represent the vertical velocity profiles accurately when we construct a structural model for realistic modelling of ground motion.

    DOI: 10.5636/eps.52.13

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  • Seismic Waves in a horizontally layered half-space with a general point source

    TAKENAKA Hiroshi, SASATANI Tsutomu

    Memoirs of the Faculty of Science, Kyushu University. Series D, Earth and planetary sciences   31 ( 1 )   19 - 28   2000

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  • Seismograph orientation at K-NET obsevatories(2) : Oita Prefecture.(共著)

    Zisin   53 ( 2 )   185 - 192   2000

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  • A hybrid PSM/FDM parallel simulation for large-scale 3-D seismic(acoustic)wavefield(共著)

    53 ( 4 )   294 - 308   2000

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  • A scheme for estimating the location and tangential plane of a reflector

    Hiroshi Takenaka

    Earth, Planets and Space   52 ( 4 )   299 - 303   2000

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    Language:English   Publisher:Springer Berlin  

    Magmatic reflectors have been detected beneath some volcanic regions by analysing some reflection phases of seismograms. In this letter we consider a problem to determine the location and tangential plane of such a reflector from the ray parameter, back-azimuth and travel time of a reflection phase, and present a scheme to solve it. It is then shown that the problem is essentially a one-dimensional root-finding problem whose independent variable is only the depth of the reflection point, and thus it can be solved by a line search method such as the one-dimensional grid search. While homogeneous velocity structure models have been used in the conventional analyses, the present scheme employs a vertically inhomogeneous one and can also easily treat converted phases at the reflector.

    DOI: 10.1186/BF03351639

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  • Seismic Waves in a horizontally layered half-space with a general point source(共著)

    Mem. Fac. Sci., Kyushu Univ., Ser. D, Earth Planet. Sci.   31 ( 1 )   19 - 28   2000

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  • An imaging technique for subsurface faults using Teleseismic-Wave Records II - Improvement in the detectability of subsurface faults

    T Murakoshi, H Takenaka, D Suetsugu

    EARTH PLANETS AND SPACE   52 ( 1 )   3 - 11   2000

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    Language:English   Publisher:TERRA SCIENTIFIC PUBL CO  

    We have developed an imaging algorithm for subsurface faults on the basis of the steepest descent method in our previous paper. In this paper we introduce two new techniques, the multi-event stacking and multi-master stacking, to improve detectability for subsurface faults. The multi-event stacking is a technique using data from plural earthquakes with different incident angles. The multi-master stacking is a technique using data of a single earthquake, in which the images obtained by employing different master receiver are stacked. We examined the feasibility of our approach using several trial models and synthetic data with different signal to noise ratios, different pulse durations and different incident angles in the two dimensional SH cases. In the numerical experiments, we could recover the image of the subsurface fault for all the trial models used, which indicates our method has a potential for sensing real subsurface faults.

    DOI: 10.5636/eps.52.3

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  • Effect of vertical velocity gradient on ground motion in a sediment-filled basin due to incident SV wave

    YB Wang, H Takenaka, T Furumura

    EARTH PLANETS AND SPACE   52 ( 1 )   13 - 24   2000

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    Language:English   Publisher:TERRA SCIENTIFIC PUBL CO  

    The natural sedimental deposits in basins show strong vertical heterogeneity in their material parameters. The aim of this paper is to investigate the effects of such vertical heterogeneity, especially vertical velocity gradient, inside basin on the seismic ground motion through the parametric study on the response of a two-dimensional semi-cylindrical sediment-filled basin to a vertical incidence of plane SV wave using the pseudospectral method. This numerical study has tried to find the effects caused by vertical velocity gradient through the use of synthetic seismograms, wavefield snapshots and surface amplitude distribution. Simulation results clearly demonstrate the derailed character of wave propagation phenomena in basins with vertical velocity gradient, which produces characteristic amplification pattern of the surface motion caused mainly by the generation of strong Rayleigh wave induced at the basin edge associated with large lateral velocity change across the basin edge. Amplification pattern at the surface strongly depends on both the vertical velocity gradient in the basin and the predominant frequency of the incident wave. Although similar phenomena on wave propagation and surface motion found in previous studies for homogeneous basin models have also been observed in this study, it has been found that the vertical velocity gradient enhances such phenomena. The results suggest that it is important to represent the vertical velocity profiles accurately when we construct a structural model for realistic modelling of ground motion.

    DOI: 10.5636/eps.52.13

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  • レシーバ関数法を用いたインドネシア地域下のマントル遷移層の厚さの推定

    斉田智治, 末次大輔, 竹中博士, 大滝寿樹, 神定健二

    日本地震学会秋季大会講演予稿集   2000   2000

  • 地震波散乱問題における積分方程式のウエーブレットを用いた解法

    竹中博士, 藤原広行

    日本地震学会秋季大会講演予稿集   2000   2000

  • A reflection/transmission matrix formulation for seismoacoustic scattering by an irregular fluid-solid interface

    T Okamoto, H Takenaka

    GEOPHYSICAL JOURNAL INTERNATIONAL   139 ( 2 )   531 - 546   1999.11

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    The seismoacoustic scattering due to an irregular fluid-solid interface (i.e. the ocean bottom) must be considered when modelling seismic wave propagation in oceanic regions. In this paper, we present an accurate method to treat this problem. The method is an extension of the reflection/transmission matrix approach that was developed to model scattering due to an irregular interface between two elastic solids. This approach uses the discrete wavenumber representation of the wavefield and the Rayleigh ansatz; the wavefield is decomposed into a set of plane waves, and: we assume that the scattered wavefield due to an incident plane wave can be expanded in terms of only the waves moving away from the interface. The plane waves at:both sides of the interface are then connected to each other based on this hypothesis and proper boundary conditions. The elements of the reflection/transmission matrices describe these connection coefficients.
    As the fluid-solid interface, the direct application of the above method is difficult because the tangential displacement at the interface is not necessarily continuous. To avoid this problem, we use pressure as the variable inside,the fluid layer. The reflection/transmission matrices between the pressure wave (i.e. the acoustic wave) and the elastic waves are then developed by using the standard boundary conditions at the fluid-solid interface (i.e. normal stress continuity, zero tangential stress, and normal displacement continuity) and the Rayleigh ansatz.
    To demonstrate the validity acid feasibility of our method, we compare the results of our method with those of other methods. First, we examine the reflection of plane elastic waves by a periodic sinusoidal interface for a single frequency. The interface profile is characterized by its periodicity or wavelength (D) and peak to trough height (h). The behaviour of the reflection calculated by our method shows almost complete agreement with that calculated by a boundary element method (BEM) up to a relatively steep interface whose height to wavelength ratio (h/D) is 0.5.
    Second, we calculate the synthetic time domain waveforms for a plane vertically incident P wave into basin-like fluid layers. We compare the waveforms calculated by the present method with those calculated by the finite difference method (FDM). In general, the waveforms calculated by the two methods match well. A quantitative study shows that the degree of agreement indicated by the RMS residuals between the waveforms of the two methods becomes better when we use a smaller grid interval in the FDM calculation. For the models treated here, the cases of 30 grid-points per wavelength results in RMS residuals less than about 10-15 per cent. This grid interval is smaller than that usually applied (more than 5-10 grid-points per wavelength). Since, in general, the accuracy of the FDM calculation becomes better as the grid interval decreases, these results indicate the validity of the present method.

    DOI: 10.1046/j.1365-246x.1999.00959.x

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  • A reflection/transmission matrix formulation for seismoacoustic scattering by an irregular fluid-solid interface

    T Okamoto, H Takenaka

    GEOPHYSICAL JOURNAL INTERNATIONAL   139 ( 2 )   531 - 546   1999.11

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    The seismoacoustic scattering due to an irregular fluid-solid interface (i.e. the ocean bottom) must be considered when modelling seismic wave propagation in oceanic regions. In this paper, we present an accurate method to treat this problem. The method is an extension of the reflection/transmission matrix approach that was developed to model scattering due to an irregular interface between two elastic solids. This approach uses the discrete wavenumber representation of the wavefield and the Rayleigh ansatz; the wavefield is decomposed into a set of plane waves, and: we assume that the scattered wavefield due to an incident plane wave can be expanded in terms of only the waves moving away from the interface. The plane waves at:both sides of the interface are then connected to each other based on this hypothesis and proper boundary conditions. The elements of the reflection/transmission matrices describe these connection coefficients.
    As the fluid-solid interface, the direct application of the above method is difficult because the tangential displacement at the interface is not necessarily continuous. To avoid this problem, we use pressure as the variable inside,the fluid layer. The reflection/transmission matrices between the pressure wave (i.e. the acoustic wave) and the elastic waves are then developed by using the standard boundary conditions at the fluid-solid interface (i.e. normal stress continuity, zero tangential stress, and normal displacement continuity) and the Rayleigh ansatz.
    To demonstrate the validity acid feasibility of our method, we compare the results of our method with those of other methods. First, we examine the reflection of plane elastic waves by a periodic sinusoidal interface for a single frequency. The interface profile is characterized by its periodicity or wavelength (D) and peak to trough height (h). The behaviour of the reflection calculated by our method shows almost complete agreement with that calculated by a boundary element method (BEM) up to a relatively steep interface whose height to wavelength ratio (h/D) is 0.5.
    Second, we calculate the synthetic time domain waveforms for a plane vertically incident P wave into basin-like fluid layers. We compare the waveforms calculated by the present method with those calculated by the finite difference method (FDM). In general, the waveforms calculated by the two methods match well. A quantitative study shows that the degree of agreement indicated by the RMS residuals between the waveforms of the two methods becomes better when we use a smaller grid interval in the FDM calculation. For the models treated here, the cases of 30 grid-points per wavelength results in RMS residuals less than about 10-15 per cent. This grid interval is smaller than that usually applied (more than 5-10 grid-points per wavelength). Since, in general, the accuracy of the FDM calculation becomes better as the grid interval decreases, these results indicate the validity of the present method.

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  • A two-point, three-dimensional seismic ray tracing using genetic algorithms

    H Sadeghi, S Suzuki, H Takenaka

    PHYSICS OF THE EARTH AND PLANETARY INTERIORS   113 ( 1-4 )   355 - 365   1999.6

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    Ray tracing between two fixed points is a boundary value problem. An initial path connecting two points, the source and the receiver, is algorithmically perturbed until it converges to a solution giving a minimum travel-time path. In multi-pathing cases, it is quite possible for an algorithm to converge to a ray path with local minimum travel time. Furthermore, when the velocity structure has discontinuities, there is another serious problem, i.e., how to determine the correct intersection between the ray and the surface of discontinuity. In this paper, a new approach for two-point ray tracing is presented, which uses genetic algorithms (GAs) to overcome these problems. Since GAs are efficient global search techniques, the proposed method guarantees to find a global minimum travel-time path and also the correct intersections. A micro-GA implementation is adopted to further enhance computational efficiency. This approach is suitable for tracing the first arriving seismic waves through a 3-D heterogeneous medium with discontinuities. The method can also find the minimum time paths of later arrivals, such as reflected and refracted waves, by constraining the ray to hit a prescribed interface. The accuracy of the method is demonstrated on the numerical examples. (C) 1999 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0031-9201(99)00011-4

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  • A two-point, three-dimensional seismic ray tracing using genetic algorithms

    H Sadeghi, S Suzuki, H Takenaka

    PHYSICS OF THE EARTH AND PLANETARY INTERIORS   113 ( 1-4 )   355 - 365   1999.6

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    Ray tracing between two fixed points is a boundary value problem. An initial path connecting two points, the source and the receiver, is algorithmically perturbed until it converges to a solution giving a minimum travel-time path. In multi-pathing cases, it is quite possible for an algorithm to converge to a ray path with local minimum travel time. Furthermore, when the velocity structure has discontinuities, there is another serious problem, i.e., how to determine the correct intersection between the ray and the surface of discontinuity. In this paper, a new approach for two-point ray tracing is presented, which uses genetic algorithms (GAs) to overcome these problems. Since GAs are efficient global search techniques, the proposed method guarantees to find a global minimum travel-time path and also the correct intersections. A micro-GA implementation is adopted to further enhance computational efficiency. This approach is suitable for tracing the first arriving seismic waves through a 3-D heterogeneous medium with discontinuities. The method can also find the minimum time paths of later arrivals, such as reflected and refracted waves, by constraining the ray to hit a prescribed interface. The accuracy of the method is demonstrated on the numerical examples. (C) 1999 Elsevier Science B.V. All rights reserved.

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  • Synthetic seismograms by using the pseudosepctral method(6) : An efficient differentiation operator for large scale 3D parallel computing

    FURUMURA Takashi, KOKETSU Kazuki, TAKENAKA Hiroshi

    100   103 - 107   1999.6

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  • Broadband strong-motion observation on the hard rock site at Kushikino.

    20 ( 3 )   89 - 98   1999

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  • 鹿児島県串木野市の岩盤上における広帯域強震観測(共著)

    九大理学部研究報告(地球惑星)   20 ( 3 )   79 - 88   1999

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  • 地震トモグラフィによる九州背弧のマントル・アップウエリング構造と九州の張力場(共著)

    月刊 地球   ( 号外27 )   211 - 216   1999

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  • 速度-応力型スタガード格子差分法を用いた2次元及び3次元地震波動計算コードの作成(共著)

    九州大学理学部研究報告(地球惑星科学)   20 ( 3 )   99 - 110   1999

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  • Seismograph orientation at K-NET observatories (1) : Western Kagoshima region

    TAKENAKA Hiroshi, WATANABE Atsushi, FUJIWARA Hiroyuki

    Sci. Repts., Dept. Earth & Planet. Sci., Kyushu Univ.   20 ( 3 )   89 - 98   1999

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  • Broadband strong-motion of observation on hard rock site at Kushikino

    Atsushi Watanabe, Yushiro Fujii, Hayato Futamure, Nobuki Kame, Hiroshi Takenaka, Sadaomi Skuzuki, Kenji Uehira, Takeshi Matsushima

    Sci. Repts., Dept. Earth & Planet. Sci., Kyushu Univ.   20 ( 3 )   79 - 88   1999

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    In 1997, two moderate earthquakes occurred in the northwestern part of Kagoshima Prefecture (Mjma 6.5 on March 26 and Mjma 6.3 on May 13), and a large number of aftershocks occurred in the southern part of the second event focal region. We started the observation of the aftershocks from April 1, 1998, at Kushikino. We used a broadband strong-motion velocity-type seismograph and an accelerograph in order to record the full waveforms of the strong ground motions. Up to April 25, 1999, we observed 74 events, and 3 events were recorded by both seismographs. In this paper, we report the detail of observational conditions and show some waveforms we obtained.

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  • Simulating seismic wave propagation in transversely isotropic media by using pseudo-spectral method(共著)

    Northwestern Seismological Journal   21 ( 2 )   212 - 224   1999

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  • Development of 2D and 3D codes of the velocity-stress staggered-grid finite-difference method for modeling seismic wave propagation

    HAYASHIDA T.

    Science Reports, Department of Earth and Planetary Sciences, Kyushu University   20 ( 3 )   99 - 110   1999

  • Simulating seismic wave propagation in transversely isotropic media by using pseudo-spectral method(共著)

    Northwestern Seismological Journal   21 ( 2 )   212 - 224   1999

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  • An efficient approach of the pseudospectral method for modelling of geometrically symmetric seismic wavefield

    H Takenaka, YB Wang, T Furumura

    EARTH PLANETS AND SPACE   51 ( 2 )   73 - 79   1999

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    The pseudospectral method is a high-accuracy numerical modelling technique that requires less computer memory and computation time than the traditional techniques such as the finite-difference method. These advantages of the pseudospectral method have enabled us to practically apply this method to modelling realistic problems that have complex structure and source models. However, a major drawback of such numerical schemes for discrete grid models is that even for rather a simple structural model they require as much computational requirements (e.g. computation time and memory) as for an entirely complex structural model with the same size of the simple one. We actually need to employ idealised simple models, such as a model with geometrical symmetry, to investigate basic phenomena of seismic waves, to develop new techniques, or to choose optimal values of some computational parameters for more complex modelling. In this paper we propose an efficient approach of an economical pseudospectral method for calculation of wavefields in models symmetric with respect to a vertical plane or two orthogonal vertical planes. Using this approach, the wavefields only need to be computed in a half or quarter domain of the models, so that the computer memory and computation time can be reduced ideally by half or quarter, respectively, as compared with the calculation of the entire models.

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  • An efficient approach of the pseudospectral method for modelling of geometrically symmetric seismic wavefield

    H Takenaka, YB Wang, T Furumura

    EARTH PLANETS AND SPACE   51 ( 2 )   73 - 79   1999

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    The pseudospectral method is a high-accuracy numerical modelling technique that requires less computer memory and computation time than the traditional techniques such as the finite-difference method. These advantages of the pseudospectral method have enabled us to practically apply this method to modelling realistic problems that have complex structure and source models. However, a major drawback of such numerical schemes for discrete grid models is that even for rather a simple structural model they require as much computational requirements (e.g. computation time and memory) as for an entirely complex structural model with the same size of the simple one. We actually need to employ idealised simple models, such as a model with geometrical symmetry, to investigate basic phenomena of seismic waves, to develop new techniques, or to choose optimal values of some computational parameters for more complex modelling. In this paper we propose an efficient approach of an economical pseudospectral method for calculation of wavefields in models symmetric with respect to a vertical plane or two orthogonal vertical planes. Using this approach, the wavefields only need to be computed in a half or quarter domain of the models, so that the computer memory and computation time can be reduced ideally by half or quarter, respectively, as compared with the calculation of the entire models.

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  • マルチバンドパスフィルターを用いたS波最大振幅解析による地震波放射特性の周波数依存に関する考察

    侭田豊, 二牟礼勇人, 竹中博士

    日本地震学会秋季大会講演予稿集   1999   1999

  • PSM/FDMハイブリッド型並列計算による地震波動の3次元数値シミュレーション

    古村孝志, こうけつ一起, 竹中博士

    日本地震学会秋季大会講演予稿集   1999   1999

  • スタガード格子差分法を用いた3次元弾性波動モデリングにおける新しい自由表面条件の適用

    林田智宏, 竹中博士, 岡元太郎

    日本地震学会秋季大会講演予稿集   1999   1999

  • Calculation of Seismic Wave Propagation in a Transversely Isotropic Cylindrical Earth Model by the Pseudospectral Method

    WANG Yanbin, TAKENAKA Hiroshi, FURUMURA Takashi

    1998 ( 2 )   1998.10

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  • 1995年兵庫県南部地震余震の地震核 (総特集 地震発生に伴う物理現象--地震発生の場と物理過程(2))

    奥村 貴史, 鈴木 貞臣, 竹中 博士

    月刊地球   20 ( 10 )   648 - 653   1998.10

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  • Parallel 3-D pseudospectral simulation of seismic wave propagation

    T Furumura, BLN Kennett, H Takenaka

    GEOPHYSICS   63 ( 1 )   279 - 288   1998.1

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    Three-dimensional pseudospectral modeling for a realistic scale problem is still computationally very intensive, even when using current powerful computers. To overcome this, we have developed a parallel pseudospectral code for calculating the 3-D wavefield by concurrent use of a number of processors. The parallel algorithm is based on a partition of the computational domain, where the field quantities are distributed over a number of processors and the calculation is concurrently done in each subdomain with interprocessor communications. Experimental performance tests using three different styles of parallel computers achieved a fairly good speed up compared with conventional computation on a single processor: maximum speed-up rate of 26 using 32 processors of a Thinking Machine CM-5 parallel computer, 1.6 using a Digital Equipment DEC-Alpha two-CPU workstation, and 4.6 using a cluster of eight Sun Microsystems SPARC-Station 10 (SPARC-10) workstations connected by an Ethernet. The result of this test agrees well with the performance theoretically predicted for each system. To demonstrate the feasibility of our parallel algorithm, we show three examples: 3-D acoustic and elastic modeling of fault-zone trapped waves and the calculation of elastic wave propagation in a 3-D syncline model.

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  • Parallel 3-D pseudospectral simulation of seismic wave propagation

    T Furumura, BLN Kennett, H Takenaka

    GEOPHYSICS   63 ( 1 )   279 - 288   1998.1

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    Three-dimensional pseudospectral modeling for a realistic scale problem is still computationally very intensive, even when using current powerful computers. To overcome this, we have developed a parallel pseudospectral code for calculating the 3-D wavefield by concurrent use of a number of processors. The parallel algorithm is based on a partition of the computational domain, where the field quantities are distributed over a number of processors and the calculation is concurrently done in each subdomain with interprocessor communications. Experimental performance tests using three different styles of parallel computers achieved a fairly good speed up compared with conventional computation on a single processor: maximum speed-up rate of 26 using 32 processors of a Thinking Machine CM-5 parallel computer, 1.6 using a Digital Equipment DEC-Alpha two-CPU workstation, and 4.6 using a cluster of eight Sun Microsystems SPARC-Station 10 (SPARC-10) workstations connected by an Ethernet. The result of this test agrees well with the performance theoretically predicted for each system. To demonstrate the feasibility of our parallel algorithm, we show three examples: 3-D acoustic and elastic modeling of fault-zone trapped waves and the calculation of elastic wave propagation in a 3-D syncline model.

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  • Sensing of faults by waveform data of intermediate-depth earthquakes(共著)

    Proceedings of the 4th SEGJ International Symposium   199 - 204   1998

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  • Pseudo-spectral modeling of seismic waves in transversely isotropic media with an arbitrary direction of symmetrical axis(共著)

    Proceedings of the 4th SEGJ International Symposium   117 - 122   1998

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  • Programming for time-frequency analysis of transient seismic signals by multiple filter technique and running spectrum technique and its application (共著)

    WANG Yanbin, TAKENAKA Hiroshi

    Mem. Fac. Sci. , Kyushu Univ. , Ser. D, Earth Planet. Sci.   30 ( 1 )   45 - 57   1998

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  • 1995年兵庫県南部地震の余震の地震核(共著)

    月刊 地球   ( 232 )   648 - 653   1998

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  • Programming for Time-frequency Analysis of Transient Seismic Signals by Multiple Filter Techniqeu and Running Spectrum Technique and Its Application

    WANG Yanbin, TAKENAKA Hiroshi

    Memoirs of the Faculty of Science, Kyushu University. Series D, Earth and planetary sciences   30 ( 1 )   45 - 57   1998

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  • 1997年鹿児島県北西部地震余震の広帯域強震観測 (共著)

    九大理学部研究報告(地球惑星)   20 ( 1 )   25 - 46   1998

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  • Recent developments in numerical methods for ground motion simulation(共著)

    The Effect of Surface Geology on Seismic Motion, Irikura, Kudo, Okada & Sasani(eds. ), Balkema, Rotterdam(ISBN : 90 5809 030 2)   1   91 - 101   1998

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  • 第16章(シミュレーション)3.1 弾性波探査

    物理探査学会編「物理探査ハンドブック」   851 - 862   1998

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  • 鹿児島県北西部地域の地震波減衰特性〜Qc-1の測定-(共著)

    自然災害西部地区部会報・論文集   ( 22 )   139 - 143   1998

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  • Sensing of faults by waveform data of intermediate-depth earthquakes(共著)

    Proceedings of the 4th SEGJ International Symposium   199 - 204   1998

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  • Pseudo-spectral modeling of seismic waves in transversely isotropic media with an arbitrary direction of symmetrical axis(共著)

    Proceedings of the 4th SEGJ International Symposium   117 - 122   1998

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  • Recent developments in numerical methods for ground motion simulation(共著)

    The Effect of Surface Geology on Seismic Motion, Irikura, Kudo, Okada & Sasani(eds. ), Balkema, Rotterdam(ISBN : 90 5809 030 2)   1   91 - 101   1998

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  • South Pacific Broadband Seismic Network. SPANET.

    末次大輔, 神定健二, 吉田康宏, 井上公, 関口渉次, 竹中博士, 斉田智治, 藤井雄士郎

    日本地震学会秋季大会講演予稿集   1998   1998

  • A recursive algorithm on the new basis for elastic waves in horizontally layered media. (II).

    斉田智治, 竹中博士

    地球惑星科学関連学会合同大会予稿集   1998   1998

  • Shear-wave anisotropy in the aftershock waveforms of the 1997 Northwestern Kagoshima earthquake. (1).

    藤井雄士郎, 竹中博士, 松島健, 馬越孝道

    地球惑星科学関連学会合同大会予稿集   1998   1998

  • Measurement of stress drop for the aftershocks of the 1997 Northwestern Kagoshima earthquakes.

    二牟礼勇人, 竹中博士, 藤井雄士郎, 松島健, 馬越孝道, 侭田豊, 鈴木貞臣

    地球惑星科学関連学会合同大会予稿集   1998   1998

  • Decay rate of coda waves and attenuation of S waves around northwestern region of Kagoshima prefecture.

    侭田豊, 竹中博士, 藤井雄士郎, 松島健, 馬越孝道, 二牟礼勇人

    地球惑星科学関連学会合同大会予稿集   1998   1998

  • Observation and waveform modeling of the aftershocks of the 1997 Northwestern Kagoshima earthquake. (2).

    藤井雄士郎, 竹中博士, 松島健, 馬越孝道, 二牟礼勇人, 鈴木貞臣

    地球惑星科学関連学会合同大会予稿集   1998   1998

  • Source process of the largest aftershock of the 1997 Northwestern Kagoshima earthquakes.

    藤井雄士郎, 竹中博士, 松島健, 馬越孝道, 鈴木貞臣

    日本地震学会秋季大会講演予稿集   1998   1998

  • The velocity-structure analysis of upper mantle using he receiver function.

    斉田智治, 末次大輔, 竹中博士

    地球惑星科学関連学会合同大会予稿集   1998   1998

  • Observation and waveform modeling of the aftershocks of the 1997 Northwestern Kagoshima earthquake

    FUJII Y, FUTAMURE H, TAKENAKA H, MATSUSHIMA T, UMAKOSHI K, TASHIRO K, SUZUKI S

    日本地震学会講演予稿集 = Programme and abstracts, the Seismological Society of Japan   1997 ( 2 )   145   1997.9

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  • Teleseismic waveform synthesis for ocean-bottom stations using a new, very effective 2.5-D finite difference technique(共著)

    Proceedings of International Workshop on Scientific Use of Submarine Cables(Feb. 25-28,1997, Okinawa Japan)   23 - 26   1997

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  • Comparison of Q(C)(-1) estimates from coda envelopes constructed from one- and multi-component seismograms

    Y Mamada, H Takenaka

    JOURNAL OF PHYSICS OF THE EARTH   45 ( 6 )   455 - 466   1997

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    Language:English   Publishing type:Rapid communication, short report, research note, etc. (scientific journal)   Publisher:CENTER ACADEMIC PUBL JAPAN  

    DOI: 10.4294/jpe1952.45.455

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  • Coda Q(-1) in Awaji Island estimated from the aftershock records of the 1995 Hyogo-ken Nanbu earthquake

    Y Mamada, T Okumura, H Takenaka, S Suzuki, S Saito, M Furumura, T Sasatani, T Matsushima, T Furumura

    JOURNAL OF PHYSICS OF THE EARTH   45 ( 2 )   147 - 154   1997

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  • Waveform analysis of the felt-earthquakes associated with the endogenous growth of the lava dome at Unzen Volcano

    OKAMATSU N.

    Unzen International workshop: decade volcano and scientific drilling, Proceedings   37 - 39   1997

  • Comparison of Q(C)(-1) estimates from coda envelopes constructed from one- and multi-component seismograms

    Y Mamada, H Takenaka

    JOURNAL OF PHYSICS OF THE EARTH   45 ( 6 )   455 - 466   1997

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  • Modelling of Strong Motion at Kikai Island due to Aftershocks of the 1995 Amami-Oshima-Kikai Earthquakes

    TAKENAKA Hiroshi, FUJII Yushiro, OKUMURA Takashi, SUZUKI Sadaomi

    Journal of Geography (Chigaku Zasshi)   106 ( 4 )   525 - 536   1997

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    Twin earthquakes (the Amami-Oshima-Kinkai Earthquakes) occurred at the southeast from Kikai Island on October 18 (MJMA 6.6) and 19 (MJMA 6.5), 1995. We observed the aftershocks at Kikai Island from October 21, 1995 to February 18, 1996 using the broadband strong-motion seismometer (VSE11C/12C). After all, we observed 40 events that include the second largest aftershock, the event of November 1 (MJMA 5.6).<BR>In this paper we model the strong-motion records of six events among the observed aftershocks, which have large amplitudes and rather simple waveforms to estimate their focal parameters (focal depth, strike, dip, rake, seismic moment and rise time), by try and error. The results suggest the following : <BR>(1) The strikes of the mainshocks of October 18 (the first mainshock) and 19 (the second mainshock) might be about N230&deg;E and N185&deg;E, respectively;<BR>(2) The hypocenter of the first mainshock might locate near the north edge of the fault which was ruptured from north to south along the fault strike, while the hypocenter of the second one might locate near the south edge of the fault which was ruptured from south to north.

    DOI: 10.5026/jgeography.106.4_525

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  • Waveform analysis of the felt earthquakes associated with the endogenous growth of the lava dome at Unzen volcano (共著)

    Proceedings of Unzen International Workshop : Decade Volcano and Scientific Drilling   37 - 39   1997

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  • Coda Q(-1) in Awaji Island estimated from the aftershock records of the 1995 Hyogo-ken Nanbu earthquake

    Y Mamada, T Okumura, H Takenaka, S Suzuki, S Saito, M Furumura, T Sasatani, T Matsushima, T Furumura

    JOURNAL OF PHYSICS OF THE EARTH   45 ( 2 )   147 - 154   1997

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    DOI: 10.4294/jpe1952.45.147

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  • Teleseismic waveform synthesis for ocean-bottom stations using a new, very effective 2.5-D finite difference technique(共著)

    Proceedings of International Workshop on Scientific Use of Submarine Cables(Feb. 25-28,1997, Okinawa Japan)   23 - 26   1997

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  • Sensing of faults by teleseismic waveform data. III. Improvement in the detectability of subsurface faults.

    村越匠, 竹中博士, 末次大輔

    地球惑星科学関連学会合同大会予稿集   1997   1997

  • A time-domain FDM for 2.5-D elastic plane-wave incidence problems.

    竹中博士, 岡元太郎, KENNETT B L N

    地球惑星科学関連学会合同大会予稿集   1997   1997

  • A ”simple” estimation method for VP/VS of a sedimentary layer by amplitudes of S and SP phases.

    竹中博士, 斉田智治, 藤井雄士郎

    地球惑星科学関連学会合同大会予稿集   1997   1997

  • A new 2.5D method for far-field body waves. Application to the 1992 Nicaraguan tsunami earthquake.

    岡元太郎, 竹中博士

    日本地震学会秋季大会講演予稿集   1997   1997

  • A very effective 2.5-D method for teleseismic body-wave synthesis.

    竹中博士, 岡元太郎, KENNETT B L N

    日本地震学会秋季大会講演予稿集   1997   1997

  • Simultaneous Observation using Broadband Seismometers. (II).

    吉田康宏, 神定健二, 金嶋聡, 大滝寿樹, 田中明子, 末次大輔, 神谷真一郎, 石原靖, 竹中博士

    日本地震学会秋季大会講演予稿集   1997   1997

  • Comparison Qc estimated from S coda envelope of vector amplitude with that of 1 component amplitude.

    侭田豊, 竹中博士

    地球惑星科学関連学会合同大会予稿集   1997   1997

  • A 2.5-D time-domain elastodynamic equation for a general anisotropic medium

    H Takenaka, BLN Kennett

    GEOPHYSICAL JOURNAL INTERNATIONAL   127 ( 2 )   F1 - F4   1996.11

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    In order to provide a quantitative analysis of real seismic records from complex regions we need to be able to calculate the wavefields in three dimensions. However, full 3-D modelling of seismic-wave propagation is still computationally intensive. An economical approach to the modelling of seismic-wave propagation which includes many important aspects of the propagation process is to examine the 3-D response of a model where the material parameters vary in two dimensions. Such a configuration, in which a 3-D wavefield is calculated for a 2-D medium, is called the '2.5-D problem'. Recently, Takenaka & Kennett (1996) proposed a 2.5-D time-domain elastodynamic equation for seismic wavefields in models with a 2-D variation in structure but obliquely incident plane waves in the absence of source. This approach is useful even for non-plane waves. In the presence of source a new 2.5-D elastodynamic equation for general anisotropic media can be derived in the time domain based on the Radon transform over slowness in the direction with constant medium properties. The approach can also be formulated in terms of velocity-stress, a representation which is well suited to the use of numerical techniques for 2-D time-domain problems such as velocity-stress finite-difference or velocity-stress pseudospectral techniques.

    DOI: 10.1111/j.1365-246X.1996.tb04716.x

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  • A 2.5-D time-domain elastodynamic equation for a general anisotropic medium

    H Takenaka, BLN Kennett

    GEOPHYSICAL JOURNAL INTERNATIONAL   127 ( 2 )   F1 - F4   1996.11

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    In order to provide a quantitative analysis of real seismic records from complex regions we need to be able to calculate the wavefields in three dimensions. However, full 3-D modelling of seismic-wave propagation is still computationally intensive. An economical approach to the modelling of seismic-wave propagation which includes many important aspects of the propagation process is to examine the 3-D response of a model where the material parameters vary in two dimensions. Such a configuration, in which a 3-D wavefield is calculated for a 2-D medium, is called the '2.5-D problem'. Recently, Takenaka & Kennett (1996) proposed a 2.5-D time-domain elastodynamic equation for seismic wavefields in models with a 2-D variation in structure but obliquely incident plane waves in the absence of source. This approach is useful even for non-plane waves. In the presence of source a new 2.5-D elastodynamic equation for general anisotropic media can be derived in the time domain based on the Radon transform over slowness in the direction with constant medium properties. The approach can also be formulated in terms of velocity-stress, a representation which is well suited to the use of numerical techniques for 2-D time-domain problems such as velocity-stress finite-difference or velocity-stress pseudospectral techniques.

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  • Elastic finite-difference modeling of strong motion in Ashigara Valley for the 1990 Odawara, Japan, earthquake

    A Pitarka, D Suetsugu, H Takenaka

    BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA   86 ( 4 )   981 - 990   1996.8

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    Finite-difference seismograms are calculated for the 1990 Odawara earthquake to model transverse and radial components of strong-motion data. Using a basin structure derived from a geotechnical survey and double-couple solution determined from P first-motion data and SH/SV amplitude ratio, two-dimensional SH and P/SV finite-difference calculation, along with correction for soft surface layers, reproduces the observed spatial variation in amplitude and waveform of the transverse and radial records at the Ashigara Valley blind prediction sites for frequencies up to 2 Hz. Comparison of the synthetic and the observed seismograms suggests that the observed spatial variation in the SH amplitude is attributed to the source radiation and amplification due to the soft surface layers, while the SV amplitude variation is controlled by the amplification due to the sedimentary basin as well as the source and surface-layer effects.

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  • A 2.5-D time-domain elastodynamic equation for plane-wave incidence

    H Takenaka, BLN Kennett

    GEOPHYSICAL JOURNAL INTERNATIONAL   125 ( 2 )   F5 - F9   1996.5

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    Full 3-D modelling of seismic wave propagation is still computationally intensive. Recently, as a compromise between realism and computational efficiency, two-and-a-half-dimensional (2.5-D) methods for calculating 3-D elastic wavefields in media varying in two dimensions have been developed. Such 2.5-D methods are an economical approach for calculating 3-D wavefields, and require a storage capacity only slightly larger than those of the corresponding 2-D calculations.
    In this paper, a 2.5-D elastodynamic equation in the time domain is constructed for seismic wavefields in models with a 2-D variation in structure but obliquely incident plane waves. The approach does not require wavenumber summation, and as a result requires much less computation time than in previous techniques. The modelling of such seismic wavefields for a 2.5-D situation with an incident plane wave is of considerable practical importance: for example, this approach can be applied to the modelling of the local response of an irregular basin structure, or to teleseismic body waveforms from shallow earthquakes occurring in subduction zones, where the laterally heterogeneous medium can have a large effect on the waveform.
    All the variables in the 2.5-D time-domain elastodynamic equation are real-valued, so the propagation characteristics can be efficiently calculated using 2-D time-domain numerical techniques such as the finite-difference method or the pseudospectral method with less computation time and memory than for other implementations.

    DOI: 10.1111/j.1365-246X.1996.tb00001.x

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  • A 2.5-D time-domain elastodynamic equation for plane-wave incidence

    H Takenaka, BLN Kennett

    GEOPHYSICAL JOURNAL INTERNATIONAL   125 ( 2 )   F5 - F9   1996.5

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    Full 3-D modelling of seismic wave propagation is still computationally intensive. Recently, as a compromise between realism and computational efficiency, two-and-a-half-dimensional (2.5-D) methods for calculating 3-D elastic wavefields in media varying in two dimensions have been developed. Such 2.5-D methods are an economical approach for calculating 3-D wavefields, and require a storage capacity only slightly larger than those of the corresponding 2-D calculations.
    In this paper, a 2.5-D elastodynamic equation in the time domain is constructed for seismic wavefields in models with a 2-D variation in structure but obliquely incident plane waves. The approach does not require wavenumber summation, and as a result requires much less computation time than in previous techniques. The modelling of such seismic wavefields for a 2.5-D situation with an incident plane wave is of considerable practical importance: for example, this approach can be applied to the modelling of the local response of an irregular basin structure, or to teleseismic body waveforms from shallow earthquakes occurring in subduction zones, where the laterally heterogeneous medium can have a large effect on the waveform.
    All the variables in the 2.5-D time-domain elastodynamic equation are real-valued, so the propagation characteristics can be efficiently calculated using 2-D time-domain numerical techniques such as the finite-difference method or the pseudospectral method with less computation time and memory than for other implementations.

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  • An efficient approach to the seismogram synthesis for a basin structure using propagation invariants

    H Takenaka, M Ohori, K Koketsu, BLN Kennett

    BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA   86 ( 2 )   379 - 388   1996.4

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    The Aki-Larner method is one of the cheapest methods for synthetic seismograms in irregularly layered media. In this article, we propose a new approach for a two-dimensional SH problem, solved originally by Aki and Larner (1970). This new approach is not only based on the Rayleigh ansatz used in the original Aki-Larner method but also uses further information on wave fields, i.e., the propagation invariants. We reduce two coupled integral equations formulated in the original Aki-Larner method to a single integral equation. Applying the trapezoidal rule for numerical integration and collocation matching, this integral equation is discretized to yield a set of simultaneous linear equations. Throughout the derivation of these linear equations, we do not assume the periodicity of the interface, unlike the original Aki-Larner method. But the final solution in the space domain implicitly includes it due to use of the same discretization of the horizontal wavenumber as the discrete wavenumber technique for the inverse Fourier transform from the wavenumber domain to the space domain.
    The scheme presented in this article is more efficient than the original Aki-Larner method. The computation time and memory required for our scheme are nearly half and one-fourth of those for the original Aki-Larner method. We demonstrate that the band-reduction technique, approximation by considering only coupling between nearby wavenumbers, can accelerate the efficiency of our scheme, although it may degrade the accuracy.

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  • An efficient approach to the seismogram synthesis for a basin structure using propagation invariants

    H Takenaka, M Ohori, K Koketsu, BLN Kennett

    BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA   86 ( 2 )   379 - 388   1996.4

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    The Aki-Larner method is one of the cheapest methods for synthetic seismograms in irregularly layered media. In this article, we propose a new approach for a two-dimensional SH problem, solved originally by Aki and Larner (1970). This new approach is not only based on the Rayleigh ansatz used in the original Aki-Larner method but also uses further information on wave fields, i.e., the propagation invariants. We reduce two coupled integral equations formulated in the original Aki-Larner method to a single integral equation. Applying the trapezoidal rule for numerical integration and collocation matching, this integral equation is discretized to yield a set of simultaneous linear equations. Throughout the derivation of these linear equations, we do not assume the periodicity of the interface, unlike the original Aki-Larner method. But the final solution in the space domain implicitly includes it due to use of the same discretization of the horizontal wavenumber as the discrete wavenumber technique for the inverse Fourier transform from the wavenumber domain to the space domain.
    The scheme presented in this article is more efficient than the original Aki-Larner method. The computation time and memory required for our scheme are nearly half and one-fourth of those for the original Aki-Larner method. We demonstrate that the band-reduction technique, approximation by considering only coupling between nearby wavenumbers, can accelerate the efficiency of our scheme, although it may degrade the accuracy.

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  • Effect of 2-D topography on the 3-D seismic wavefield using a 2.5-D discrete wavenumber-boundary integral equation method

    H Takenaka, BLN Kennett, H Fujiwara

    GEOPHYSICAL JOURNAL INTERNATIONAL   124 ( 3 )   741 - 755   1996.3

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    A full treatment of topographic effects on the seismic wavefield requires a 3-D treatment of the topography and a 3-D calculation for the wavefield. However, such full 3-D calculations are still very expensive to perform. An economical approach, which does not require the same level of computational resources as full 3-D modelling, is to examine the 3-D response of a model in which the heterogeneity pattern is 2-D (the so-called 2.5-D problem). Such 2.5-D methods can calculate 3-D wavefields without huge computer memory requirements, since they require storage nearly equal to that of the corresponding 2-D calculations.
    In this paper, we consider wave propagation from a point source in the presence of 2-D irregular topography, and develop a computational method for such 2.5-D wave-propagation problems. This approach is an extension to the 2.5-D case of the discrete wavenumber-boundary integral equation method introduced by Bouchon (1985) and Gaffet & Bouchon (1989) to study 2-D topographic problems. One of the most significant advantages of the 2.5-D calculations is that calculations are performed for a point source and so it is possible for us to take into account the 3-D radiation pattern from the source. We demonstrate that this discrete wavenumber-boundary integral equation procedure, coupled with a Green's function decomposition into P-and S-wave contributions, provides a flexible and effective means of evaluating the wavefield.

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  • 2.5-D modelling of elastic waves using the pseudospectral method

    T Furumura, H Takenaka

    GEOPHYSICAL JOURNAL INTERNATIONAL   124 ( 3 )   820 - 832   1996.3

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    The pseudospectral method is a high-accuracy numerical modelling technique which requires less memory and CPU time than traditional numerical modelling techniques, such as finite difference. However, full 3-D modelling is still computationally intensive. As we must compromise between realism and computational efficiency, we have developed a 2.5-D pseudospectral scheme for calculating 3-D elastic wavefields in media varying in two dimensions. To demonstrate the feasibility of the scheme described in this paper, we use data from a refraction survey carried out in 1984 by the Explosion Seismology Group in the southeastern foothills of the Hidaka Mountains, Hokkaido, Japan.

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  • 2.5-D modelling of elastic waves using the pseudospectral method

    T Furumura, H Takenaka

    GEOPHYSICAL JOURNAL INTERNATIONAL   124 ( 3 )   820 - 832   1996.3

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    The pseudospectral method is a high-accuracy numerical modelling technique which requires less memory and CPU time than traditional numerical modelling techniques, such as finite difference. However, full 3-D modelling is still computationally intensive. As we must compromise between realism and computational efficiency, we have developed a 2.5-D pseudospectral scheme for calculating 3-D elastic wavefields in media varying in two dimensions. To demonstrate the feasibility of the scheme described in this paper, we use data from a refraction survey carried out in 1984 by the Explosion Seismology Group in the southeastern foothills of the Hidaka Mountains, Hokkaido, Japan.

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  • Effect of 2-D topography on the 3-D seismic wavefield using a 2.5-D discrete wavenumber-boundary integral equation method

    H Takenaka, BLN Kennett, H Fujiwara

    GEOPHYSICAL JOURNAL INTERNATIONAL   124 ( 3 )   741 - 755   1996.3

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    A full treatment of topographic effects on the seismic wavefield requires a 3-D treatment of the topography and a 3-D calculation for the wavefield. However, such full 3-D calculations are still very expensive to perform. An economical approach, which does not require the same level of computational resources as full 3-D modelling, is to examine the 3-D response of a model in which the heterogeneity pattern is 2-D (the so-called 2.5-D problem). Such 2.5-D methods can calculate 3-D wavefields without huge computer memory requirements, since they require storage nearly equal to that of the corresponding 2-D calculations.
    In this paper, we consider wave propagation from a point source in the presence of 2-D irregular topography, and develop a computational method for such 2.5-D wave-propagation problems. This approach is an extension to the 2.5-D case of the discrete wavenumber-boundary integral equation method introduced by Bouchon (1985) and Gaffet & Bouchon (1989) to study 2-D topographic problems. One of the most significant advantages of the 2.5-D calculations is that calculations are performed for a point source and so it is possible for us to take into account the 3-D radiation pattern from the source. We demonstrate that this discrete wavenumber-boundary integral equation procedure, coupled with a Green's function decomposition into P-and S-wave contributions, provides a flexible and effective means of evaluating the wavefield.

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  • Imaging of Subsurface Faults Using Teleseismic Waveform -Numerical Experiments-

    MURAKOSHI Takumi, TAKENAKA Hiroshi, SUETSUGU Daisuke, SAITA Tomoharu

    Zisin (Journal of the Seismological Society of Japan. 2nd ser.)   49 ( 3 )   389 - 401   1996

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    We develop a method for imaging subsurface faults using teleseismic waveform data. The target of our method is not an entire velocity structure, but location and size of a subsurface fault. The method consists of the following steps:<br>(1) pre-processing of observed records, <br>(2) selection of trial model (initial model of structure), <br>(3) estimation of incident wavefield from the bottom of the studied region, <br>(4) forward calculation, <br>(5) calculation of the steepest descent direction of the model parameters, <br>(6) image analysis and identification of faults.<br>The idea of the method has been originally proposed by TAKENAKA et al. (1996). In the present paper we examine the feasibility of the approach using the synthetic data and several trial models in the two dimensional SH cases. We also here propose a practical technique to estimate the incident wavefield from the observed data. In the numerical examination, we could recover the image of the subsurface fault for all trial models we used, which indicates our method has potentiality for sensing real subsurface faults and encourages further development of the method.

    DOI: 10.4294/zisin1948.49.3_389

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  • Imaging of subsurface faults using teleseismic waveform -Numerical experiments-(共著)

    MURAKOSHI Takumi, TAKENAKA Hiroshi, SUETSUGU Daisuke, SAITA Tomoharu

    Zisin(J. Seism. Soc. Japan)   49 ( 3 )   389 - 401   1996

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    We develop a method for imaging subsurface faults using teleseismic waveform data. The target of our method is not an entire velocity structure, but location and size of a subsurface fault. The method consists of the following steps:<br>(1) pre-processing of observed records, <br>(2) selection of trial model (initial model of structure), <br>(3) estimation of incident wavefield from the bottom of the studied region, <br>(4) forward calculation, <br>(5) calculation of the steepest descent direction of the model parameters, <br>(6) image analysis and identification of faults.<br>The idea of the method has been originally proposed by TAKENAKA et al. (1996). In the present paper we examine the feasibility of the approach using the synthetic data and several trial models in the two dimensional SH cases. We also here propose a practical technique to estimate the incident wavefield from the observed data. In the numerical examination, we could recover the image of the subsurface fault for all trial models we used, which indicates our method has potentiality for sensing real subsurface faults and encourages further development of the method.

    DOI: 10.4294/zisin1948.49.3_389

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  • An imaging technique for subsurface faults using teleseismic-wave records - SH case

    H Takenaka, T Murakoshi, D Suetsugu, T Furumura

    JOURNAL OF PHYSICS OF THE EARTH   44 ( 5 )   529 - 541   1996

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    It is important for disaster prevention and public safety design to know whether subsurface faults exist, not only in Kobe, which was heavily damaged by the 1995 Hyogo-ken Nanbu earthquake, but also in any urban area which is tectonically active. However, there is still little information on subsurface faults. In this paper, we propose a new approach for sensing subsurface faults using teleseismic-wave array records. Our new method employs an imaging technique similar to the reflection method, but is much less expensive and can be used in urban areas. The target of our method is not the velocity structure itself, but rather the position and size of a subsurface fault. The imaging algorithm is based on the steepest descent method, which is also used in waveform inversion of reflection data. However, since iteration is not required by our approach, only one forward computation together with reverse-time computation of the wavefield is required. The method proposed in this paper consists of the following steps: 1) pre-processing observed records, 2) forward calculation, 3) calculation of the steepest descent direction of the model parameters, and 4) image analysis and identification of faults. The feasibility of the method is demonstrated using SH synthetic data.

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  • An imaging technique for subsurface faults using teleseismic-wave records - SH case

    H Takenaka, T Murakoshi, D Suetsugu, T Furumura

    JOURNAL OF PHYSICS OF THE EARTH   44 ( 5 )   529 - 541   1996

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    It is important for disaster prevention and public safety design to know whether subsurface faults exist, not only in Kobe, which was heavily damaged by the 1995 Hyogo-ken Nanbu earthquake, but also in any urban area which is tectonically active. However, there is still little information on subsurface faults. In this paper, we propose a new approach for sensing subsurface faults using teleseismic-wave array records. Our new method employs an imaging technique similar to the reflection method, but is much less expensive and can be used in urban areas. The target of our method is not the velocity structure itself, but rather the position and size of a subsurface fault. The imaging algorithm is based on the steepest descent method, which is also used in waveform inversion of reflection data. However, since iteration is not required by our approach, only one forward computation together with reverse-time computation of the wavefield is required. The method proposed in this paper consists of the following steps: 1) pre-processing observed records, 2) forward calculation, 3) calculation of the steepest descent direction of the model parameters, and 4) image analysis and identification of faults. The feasibility of the method is demonstrated using SH synthetic data.

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  • Numerical 3-D modeling of seismic waves by the pseudospectral method(共著)

    Butsuri-Tansa(J. SEGJ)   49 ( 6 )   536 - 548   1996

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  • 1995年奄美大島近海地震余震の喜界島における広帯域震観測(共著)

    九州大学理学部研究報告(地球惑星科学)   19 ( 2 )   173 - 189   1996

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  • Pseudospectral法による地震波動の3次元計算(共著)

    物理探査   49 ( 6 )   536 - 548   1996

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  • Broadband strong-motion observation in Kikai Island for aftershocks of the 1995 Amamioshima-Kinkai earthquake(共著)

    Science Reports, Department of Earth and Planetary Sciences, Kyushu University   19 ( 2 )   173 - 189   1996

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  • Sensing of subsurface faults based on an imaging technique for teleseismic waveform data II-Feasibility study for application to oblique incidence, multi-event and noise data.

    村越匠, 竹中博士, 末次大輔, 斉田智治, 古村孝志

    物理探査学会学術講演会講演論文集   94th   1996

  • A reflection/transmission matrix formulation for elastic-wave scattering by an irregular fluid-solid interface.

    岡元太郎, 竹中博士

    地球惑星科学関連学会合同大会予稿集   1996   1996

  • Surface-layer correction for numerical solutions of seismic waves.

    斉田智治, 竹中博士, PITARKA A, 末次大輔

    地球惑星科学関連学会合同大会予稿集   1996   1996

  • Broadband strong-motion observation of aftershocks of ’95 Amamioshima-kinkai earthquake in Kikai Island.

    藤井雄士郎, 奥村貴史, 竹中博士, 鈴木貞臣

    地球惑星科学関連学会合同大会予稿集   1996   1996

  • An extended profile of the explosion seismic observation in Unzen volcano, Kyushu.

    鈴木貞臣, 勝俣啓, 山崎義典, 三浪俊夫, 石原和彦, 竹中博士

    地球惑星科学関連学会合同大会予稿集   1996   1996

  • Sensing of faults for teleseismic wave form data. Feasibility study for application to multi-event and noise data.

    村越匠, 竹中博士, 末次大輔

    日本地震学会秋季大会講演予稿集   1996   1996

  • 3.9.1.6 地震波伝播の3次元数値シミュレーションに関する研究(3.9.1 関係機関との共同研究,3.9 共同研究,3. 研究業務)

    藤原 広行, 竹中 博士

    防災科学技術研究所年報   5   57 - 57   1995.3

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  • 3.4.2(2) 不均質媒質における地震波伝播の理論並びにその地下構造推定への応用に関する研究(3.4.2 科学技術特別研究員,3.4 科学技術振興費による研究,3. 研究業務)

    竹中 博士

    防災科学技術研究所年報   5   40 - 40   1995.3

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  • A WRAPAROUND ELIMINATION TECHNIQUE FOR THE PSEUDOSPECTRAL WAVE SYNTHESIS USING AN ANTIPERIODIC EXTENSION OF THE WAVE-FIELD

    T FURUMURA, H TAKENAKA

    GEOPHYSICS   60 ( 1 )   302 - 307   1995.1

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    Language:English   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   Publisher:SOC EXPLORATION GEOPHYSICISTS  

    DOI: 10.1190/1.1443760

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  • Modeling seismic wave propagation in complex media

    H Takenaka

    JOURNAL OF PHYSICS OF THE EARTH   43 ( 3 )   351 - 368   1995

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    We review the studies on modeling seismic wave propagation in complex media, which were carried out during the past 10 years by researchers at Japanese institutions. Special emphasis is placed on those works which are perceived as important but had little exposure outside Japan. We can say that the fundamental development of method for seismogram synthesis in the (3, 1) dimension was completed, where the first and second numbers in parentheses are the space dimensions of the wavefield and the heterogeneity of the medium. However, seismologists have been eager to model seismic propagation in the (2, 2), (3, 2), and (3, 3) dimensions during the last 10 years. Modeling seismic wave propagation in a full (3, 3) dimension is now limited to simple small-scale problems because of the extensive computation and large memory, even when using a supercomputer. Nevertheless, in laterally and vertically heterogeneous media, we have to calculate 3-dimensional wavefields in order to analyze real seismic records quantitatively. There exist two potential breakthroughs. One is to assume the medium is axisymmetric and the other to model(3, 2) dimensional wave propagation (the so-called 2.5 dimensional problem). Numerical methods have the potential to simulate seismic wave propagation in realistic environments of substantial spatio-temporal extent. Since we are not used to processing such an abundance of information, we have to investigate methods for analyzing and interpreting large volumes of computational data. These studies may well challenge our conception of seismic wave propagation.

    DOI: 10.4294/jpe1952.43.351

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  • Aftershock observation of the 1995 Hyogo-ken Nanbu earthquake in Awaje Island : strong motion and broad band observation(共著)

    Sci. Repts. , Dept. Earth & Planet. Sci. , Kyushu Univ.   19 ( 1 )   103 - 123   1995

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  • A wraparound elimination technique for the pseudospectral wave synthesis using an antiperiodic extension of the wavefield(共著)

    Geophysics   60 ( 1 )   302 - 307   1995

  • 淡路島における1995年兵庫県南部地震の余震観測-強震動及び広帯域余震観測-(共著)

    九州大学理学部研究報告(地球惑星科学)   19 ( 1 )   103 - 123   1995

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  • TREATMENT OF AN INFINITELY EXTENDED FREE-SURFACE FOR INDIRECT FORMULATION OF THE BOUNDARY-ELEMENT METHOD

    T YOKOI, H TAKENAKA

    JOURNAL OF PHYSICS OF THE EARTH   43 ( 1 )   79 - 103   1995

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    A new approach which uses the full-space Green's function is proposed to eliminate the influence of the finitude of the segmented free surface in the indirect formulation of the Boundary Element Method. The absence of a contribution from the far parts of the free surface that are neglected in the computation is compensated for, assuming that the wave field along flat parts of the surface far from the localized irregularity can be substituted by the reference solution, i.e., the wave field in the half space with a completely flat free surface which is given analytically. The nonphysical waves radiated at the two ends of the segmented model of the free surface are eliminated efficiently by this approach. This reduces the amount of computer main memory required and the CPU time consumed for calculation. Moreover, physical consideration of the relation to existing approaches shows clearly that our approach gives a more precise approximation, in particular for high frequency problems. The capacity of the indirect formulation of the Boundary Element Method therefore is bettered by this approach.

    DOI: 10.4294/jpe1952.43.79

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  • Modeling seismic wave propagation in complex media

    Hiroshi Takenaka

    Journal of Physics of the Earth   43 ( 3 )   351 - 368   1995

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    We review the studies on modeling seismic wave propagation in complex media, which were carried out during the past 10 years by researchers at Japanese institutions. Special emphasis is placed on those works which are perceived as important but had little exposure outside Japan. We can say that the fundamental development of method for seismogram synthesis in the (3, 1) dimension was completed, where the first and second numbers in parentheses are the space dimensions of the wavefield and the heterogeneity of the medium. However, seismologists have been eager to model seismic propagation in the (2, 2), (3, 2), and (3, 3) dimensions during the last 10 years. Modeling seismic wave propagation in a full (3, 3) dimension is now limited to simple small-scale problems because of the extensive computation and large memory, even when using a supercomputer. Nevertheless, in laterally and vertically heterogeneous media, we have to calculate 3-dimensional wavefields in order to analyze real seismic records quantitatively. There exist two potential breakthroughs. One is to assume the medium is axisymmetric and the other to model (3, 2) dimensional wave propagation (the so-called 2.5 dimensional problem). Numerical methods have the potential to simulate seismic wave propagation in realistic environments of substantial spatio-temporal extent. Since we are not used to processing such an abundance of information, we have to investigate methods for analyzing and interpreting large volumes of computational data. These studies may well challenge our conception of seismic wave propagation. © 1995, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan. All rights reserved.

    DOI: 10.4294/jpe1952.43.351

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  • Treatment of an infinitely extended free surface for indirect formulation of the boundary element method(共著)

    Toshiaki Yokoi, Hiroshi Takenaka

    J. Phys. Earth   43 ( 1 )   79 - 103   1995

  • A numerical generator of low-frequency earthquakes.

    竹中博士, 後藤章夫

    日本火山学会講演予稿集   1995   1995

  • Synthetic seismograms by using the Pseudospectral method. (9). The possibility of parallel computation for three-dimensional modeling.

    古村孝志, 竹中博士

    地球惑星科学関連学会合同大会予稿集   1995   1995

  • A recursive algorithm on the new basis for elastic waves in horizontally layered media.

    斉田智治, 竹中博士, GELLER R J, 羽鳥友彦

    地球惑星科学関連学会合同大会予稿集   1995   1995

  • A numerical generator of monochromatic events.

    竹中博士, 後藤章夫

    日本地震学会秋季大会講演予稿集   1995   1995

  • Sensing of faults for teleseismic wave form data. Numerical experiments.

    村越匠, 竹中博士, 末次大輔, 古村孝志

    日本地震学会秋季大会講演予稿集   1995   1995

  • Seismic Activities Associated with Ground Deformation at the Summit of Unzen Volcano.

    清水洋, 松尾のり道, 馬越孝道, 松島健, 竹中博士

    地球惑星科学関連学会合同大会予稿集   1995   1995

  • Sensing of subsurface faults based on an imaging technique for teleseismic wave form data. numerical experiments.

    村越匠, 竹中博士, 末次大輔, 古村孝志

    物理探査学会学術講演会講演論文集   92nd   1995

  • A recursive algorithm on the new basis for elastic waves in horizontally layered media.

    斉田智治, 竹中博士, 羽鳥友彦, GELLER R J

    物理探査学会学術講演会講演論文集   92nd   1995

  • MODELING STRONG-MOTION IN THE ASHIGARA VALLEY FOR THE 1990 ODAWARA, JAPAN, EARTHQUAKE

    AS PITARKA, H TAKENAKA, D SUETSUGU

    BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA   84 ( 5 )   1327 - 1335   1994.10

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    Finite-difference seismograms are calculated for the 1990 Odawara earthquake. Using a basin structure derived from a geotechnical survey and a double-couple solution determined from the P first-motion data, a two-dimensional SH finite-difference calculation reproduces the observed spatial variation in amplitude and waveform of the transverse records at the Ashigara Valley Blind Prediction Sites for frequencies lower than 2 Hz. Comparison of the synthetics and the observed seismograms suggests that the observed amplitude variation of the transverse records in the Ashigara Valley is mainly due to the source radiation pattern rather than the basin structure. Several different double couples are used in the waveform modeling to show the sensitivity of ground motion to the source mechanism. We thus conclude that it is important to use an appropriate focal mechanism to model near-field ground motion.

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  • MODELING STRONG-MOTION IN THE ASHIGARA VALLEY FOR THE 1990 ODAWARA, JAPAN, EARTHQUAKE

    AS PITARKA, H TAKENAKA, D SUETSUGU

    BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA   84 ( 5 )   1327 - 1335   1994.10

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    Finite-difference seismograms are calculated for the 1990 Odawara earthquake. Using a basin structure derived from a geotechnical survey and a double-couple solution determined from the P first-motion data, a two-dimensional SH finite-difference calculation reproduces the observed spatial variation in amplitude and waveform of the transverse records at the Ashigara Valley Blind Prediction Sites for frequencies lower than 2 Hz. Comparison of the synthetics and the observed seismograms suggests that the observed amplitude variation of the transverse records in the Ashigara Valley is mainly due to the source radiation pattern rather than the basin structure. Several different double couples are used in the waveform modeling to show the sensitivity of ground motion to the source mechanism. We thus conclude that it is important to use an appropriate focal mechanism to model near-field ground motion.

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  • CALCULATION OF SURFACE-WAVES FOR A THIN BASIN STRUCTURE USING A DIRECT BOUNDARY-ELEMENT METHOD WITH NORMAL-MODES

    H FUJIWARA, H TAKENAKA

    GEOPHYSICAL JOURNAL INTERNATIONAL   117 ( 1 )   69 - 91   1994.4

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    An efficient method to synthesize surface waves in a thin sedimentary basin exhibiting lateral heterogeneities is proposed. This method is based on the direct boundary element method; that is, it represents the wavefield by integral equations along boundaries. The excitation and propagation of surface waves by lateral heterogeneities are incorporated into the numerical scheme by using propagation operators and superposition, where the Green's function is computed by the summation of normal modes when the horizontal distance between the source and receiver is large, which reduces computation costs. Using the properties of the surface-wave part of Green's function, the number of elements needed for discretization can be reduced. This formulation can be effective for both the physical interpretation of certain observed phases and for numerical calculations, In this paper, only 2-D SH problems are considered, and the extension to 2-D P-SV problems and 3-D problems is discussed briefly.

    DOI: 10.1111/j.1365-246X.1994.tb03304.x

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  • CALCULATION OF SURFACE-WAVES FOR A THIN BASIN STRUCTURE USING A DIRECT BOUNDARY-ELEMENT METHOD WITH NORMAL-MODES

    H FUJIWARA, H TAKENAKA

    GEOPHYSICAL JOURNAL INTERNATIONAL   117 ( 1 )   69 - 91   1994.4

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    An efficient method to synthesize surface waves in a thin sedimentary basin exhibiting lateral heterogeneities is proposed. This method is based on the direct boundary element method; that is, it represents the wavefield by integral equations along boundaries. The excitation and propagation of surface waves by lateral heterogeneities are incorporated into the numerical scheme by using propagation operators and superposition, where the Green's function is computed by the summation of normal modes when the horizontal distance between the source and receiver is large, which reduces computation costs. Using the properties of the surface-wave part of Green's function, the number of elements needed for discretization can be reduced. This formulation can be effective for both the physical interpretation of certain observed phases and for numerical calculations, In this paper, only 2-D SH problems are considered, and the extension to 2-D P-SV problems and 3-D problems is discussed briefly.

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  • 3.4.2(2) 不均質媒質における地震波伝播の理論並びにその地下構造推定への応用に関する研究(3.4.2 科学技術特別研究員,3.4 科学技術振興費による研究,3. 研究業務)

    竹中 博士

    防災科学技術研究所年報   4   41 - 41   1994.3

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  • 北海道南西沖地震に伴う津波-小樽から礼文島まで-(共著)

    月刊海洋   号外 ( 7 )   153 - 158   1994

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  • Surface waves in a sedimentary basin(共著)

    469 - 474   1994

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  • 堆積盆地内で発生する表面波(共著)

    第9回日本地震工学シンポジウム(1994)論文集,第1分冊   469 - 474   1994

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  • Visualization of the wavefield synthesized by using a numerical simuration method.

    古村孝志, 竹中博士, 岡部成玄

    情報処理学会夏のプログラミング・シンポジウム報告集   1993   1994

  • Non-linear Elastic Waveform Inversion for Heterogeneous Earth Structure. A Numerical Test.

    末次大輔, PITARKA A S, 竹中博士

    日本地震学会秋季大会講演予稿集   1994   1994

  • Synthetic seismograms by using the Pseudospectral method. (8). Free-surface boundary condition and its stability of the computation.

    古村孝志, 竹中博士

    日本地震学会秋季大会講演予稿集   1994   1994

  • Synthetic seismograms by using the Pseudospectral method. (7). High-frequency noise reduction for the stabilization of the computation.

    古村孝志, 竹中博士

    地球惑星科学関連学会合同大会予稿集   1994   1994

  • Source Characteristics of the Ashio Earthquake Swarm.

    木下繁夫, 藤原広行, 池田隆司, 竹中博士, 吉本和生, 佐藤春夫

    地球惑星科学関連学会合同大会予稿集   1994   1994

  • THE INTEGRAL OPERATOR REPRESENTATION OF PROPAGATION INVARIANTS FOR ELASTIC-WAVES IN IRREGULARLY LAYERED MEDIA

    H TAKENAKA, BLN KENNETT, K KOKETSU

    WAVE MOTION   17 ( 4 )   299 - 317   1993.8

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    The reflection and transmission of elastic waves in irregularly layered media can be represented in terms of a set of propagation invariants for elastic wavefields. There are a number of such invariants depending on different integral operators acting on the displacement and traction fields. By exploiting different classes of invariants, representations for reflection and transmission operators at an irregular interface can be derived which are easier to compute than previous forms.
    In a similar way, a simplified representation for the surface amplification factor for incident waves on a free surface can be constructed. This is particularly useful for calculating theoretical seismograms on the surface of a body.

    DOI: 10.1016/0165-2125(93)90010-D

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  • THE INTEGRAL OPERATOR REPRESENTATION OF PROPAGATION INVARIANTS FOR ELASTIC-WAVES IN IRREGULARLY LAYERED MEDIA

    H TAKENAKA, BLN KENNETT, K KOKETSU

    WAVE MOTION   17 ( 4 )   299 - 317   1993.8

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    The reflection and transmission of elastic waves in irregularly layered media can be represented in terms of a set of propagation invariants for elastic wavefields. There are a number of such invariants depending on different integral operators acting on the displacement and traction fields. By exploiting different classes of invariants, representations for reflection and transmission operators at an irregular interface can be derived which are easier to compute than previous forms.
    In a similar way, a simplified representation for the surface amplification factor for incident waves on a free surface can be constructed. This is particularly useful for calculating theoretical seismograms on the surface of a body.

    DOI: 10.1016/0165-2125(93)90010-D

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  • 3.4.2(3) 不均質媒質における地震波伝播の理論並びにその地下構造推定への応用に関する研究(3.4.2 科学技術特別研究員,3.4 科学技術振興費による研究,3. 研究業務)

    竹中 博士

    防災科学技術研究所年報   3   50 - 50   1993.3

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  • 不整型地盤における地震波動の数値計算法

    竹中博士

    地震2   42   391 - 403   1993

  • Reduction of the Memory Consumption in the Aki-Larner Method

    OHORI Michihiro, TAKENAKA Hiroshi, KOKETSU Kazuki, MINAMI Tadao

    Zisin (Journal of the Seismological Society of Japan. 2nd ser.)   45 ( 4 )   357 - 363   1993

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    Aki-Larner method (ALM) is a very powerful technique to calculate the seismic responses of layered media having irregular interfaces. However, it is necessary to solve complex simultaneous equations with very large full matrices so that it takes very long time and consume much memory. Recently, Ohminato et al. (1990) proposed a Galerkin method and suggested that wavenumber coupling between far separated elements in the submatrices of the full matrices are very week if the lateral irregurality is gentle. Their idea seems to be applicable to the analyses of ALM, too. Therefore, in this paper, we estimated possible reduction of the memory consumption in the ALM by neglecting most of non-diagonal elements of the submatrices. Through the 2-dimensional (2-D) analyses, we calculated responses due to vertically incident plane SH-wave and studied the effect of the neglect of non-diagonal submatrix elements on the accuracy of results. Six types of alluvial valleys with different shape were used and the error caused by the neglect was evaluated in comparison with results obtained by the conventional ALM. As a result, we can treat submatrices as band matrices with 1/4 or 1/6 width if the lateral irregularity is gentle, and this leads to reduction of the memory consumption in the Aki-Larner method for the simulation in high frequencies or 3-D problems.

    DOI: 10.4294/zisin1948.45.4_357

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  • Is the fast Hartley transform more efficient than FFT? (共著)

    Furumura Takashi, Takenaka Hirosi, Ninomiya Ichizo

    Transactions of the Japan Society for Industrial and Applied Mathematics   3 ( 3 )   245 - 255   1993

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    This paper discusses the effectiveness of the fast Hartley transform(FHT) when it is applied to some signal processing problems. FHT is a real-valued transform and is quite similar to the fast Fourier transform(FFT) except the properties such as the reciprocity of the transform. In the last decade, more than dozens of papers have been published with the assertion that FHT offers an alternative to FFT with the advantage of its time and memory-space. In the present paper, we discuss that FHT has no explicit advantage over real-valued FFT in terms of the computation based on our comparative experiment.

    DOI: 10.11540/jsiamt.3.3_245

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  • Computational methods for seismic wave propagation in complex subsurface structures

    TAKENAKA H.

    Zisin   46 ( 2 )   191 - 205   1993

  • 不整形地盤における波動伝播の数値計算法

    地震   46 ( 2 )   191 - 205   1993

  • Reduction of the memory consumption in the Aki-Larner method(共著)

    OHORI Michihiro, TAKENAKA Hiroshi, KOKETSU Kazuki, MINAMI Tadao

    Zisin   45 ( 4 )   357 - 363   1993

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    Language:Japanese   Publisher:SEISMOLOGICAL SOCIETY OF JAPAN  

    Aki-Larner method (ALM) is a very powerful technique to calculate the seismic responses of layered media having irregular interfaces. However, it is necessary to solve complex simultaneous equations with very large full matrices so that it takes very long time and consume much memory. Recently, Ohminato et al. (1990) proposed a Galerkin method and suggested that wavenumber coupling between far separated elements in the submatrices of the full matrices are very week if the lateral irregurality is gentle. Their idea seems to be applicable to the analyses of ALM, too. Therefore, in this paper, we estimated possible reduction of the memory consumption in the ALM by neglecting most of non-diagonal elements of the submatrices. Through the 2-dimensional (2-D) analyses, we calculated responses due to vertically incident plane SH-wave and studied the effect of the neglect of non-diagonal submatrix elements on the accuracy of results. Six types of alluvial valleys with different shape were used and the error caused by the neglect was evaluated in comparison with results obtained by the conventional ALM. As a result, we can treat submatrices as band matrices with 1/4 or 1/6 width if the lateral irregularity is gentle, and this leads to reduction of the memory consumption in the Aki-Larner method for the simulation in high frequencies or 3-D problems.

    DOI: 10.4294/zisin1948.45.4_357

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  • 高速ハートレ変換は高速フーリエ変換を越えるか?(共著)

    日本応用数理学会論文誌   3 ( 3 )   245 - 255   1993

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  • A Field Survey of Tsunami Generated by the Hokkaido-Nansei-Oki Earthquake. From Otaru to Rebun Island.

    後藤章夫, 高橋浩晃, 宇津木充, 小野忍, 西田泰典, 大島弘光, 笠原稔, 竹中博士, 斉田智治

    日本地震学会秋季大会講演予稿集   1993   1993

  • Calculation of three-dimentional elastic wave field in two dimensional structure using BEM.

    藤原広行, 竹中博士

    日本地震学会秋季大会講演予稿集   1993   1993

  • Visualization of reciprocity by using a numerical simulation method.

    古村孝志, 竹中博士

    日本地震学会秋季大会講演予稿集   1993   1993

  • Near-field Observation of Small Earthquakcs Occurring in the Dome of Unzen Volcano

    Goto Susumu, Suzuki Sadaomi, Takenaka Hiroshi, Shimizu Hiroshi

    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN   1993   63 - 63   1993

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    DOI: 10.18940/vsj.1993.2.0_63

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  • 端に不連続を持つデータのためのFourier微分法-対称法-(共著)

    FURUMURA T.

    物理探査   45 ( 4 )   303 - 309   1992

  • Numerical simulation and visualization of seismic wavefield(共著)

    FURUMURA T.

    Rep. Cent. Infor. Process. Educ., Center for Information Processing Education, Hokkaido Univ.   11 ( 11 )   25 - 34   1992

  • 地震動の数値シミュレーションの波動場の可視化(共著)

    北海道大学情報処理教育センター広報   ( 11 )   25 - 34   1992

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  • Effect of 2-D Mountain Topography on the 3-D Seismic Wavefield : Isotropic P-wave Source

    Takenaka H., Kennett B. L. N.

    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN   1992   35 - 35   1992

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    DOI: 10.18940/vsj.1992.2.0_35

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  • 2-D REFLECTIVITY METHOD AND SYNTHETIC SEISMOGRAMS FOR IRREGULARLY LAYERED STRUCTURES .2. INVARIANT EMBEDDING APPROACH

    K KOKETSU, BLN KENNETT, H TAKENAKA

    GEOPHYSICAL JOURNAL INTERNATIONAL   105 ( 1 )   119 - 130   1991.4

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    Laterally varying interfaces cause coupling between wavenumbers so that seismograms in two-dimensionally layered media can be synthesized by means of 'supermatrices', which include the coupled contributions of all the wavenumbers. We introduce reflection and transmission 'supermatrices' in order to eliminate numerical problems arising from loss of precision for evanescent waves in the seismogram synthesis. An interface is assumed to be such that the reflected and transmitted wavefields on its two sides can be represented as purely upgoing and downgoing waves, i.e. the Rayleigh ansatz is imposed. The computational demands of this method can be kept to a minimum by exploiting propagation invariants in the coupled wavenumber domain.
    The superior performance of this 'invariant embedding' approach when compared to propagator or finite difference schemes is illustrated by application to the response of sedimentary basins to excitation by an incident plane wave or a line force. The results are in good general agreement with the other methods, but show greater numberical stability and computational efficiency. In the case of a single interface the 'invariant embedding' procedure for P-SV-waves takes 45 per cent less computation time and 29 per cent less memory than the propagator method of Koketsu (1987a, b). The gains are reduced in a multilayer case because of the level of computation required to calculate the addition rules for the large reflection and transmission supermatrices.

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  • 2-D REFLECTIVITY METHOD AND SYNTHETIC SEISMOGRAMS FOR IRREGULARLY LAYERED STRUCTURES .2. INVARIANT EMBEDDING APPROACH

    K KOKETSU, BLN KENNETT, H TAKENAKA

    GEOPHYSICAL JOURNAL INTERNATIONAL   105 ( 1 )   119 - 130   1991.4

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    Laterally varying interfaces cause coupling between wavenumbers so that seismograms in two-dimensionally layered media can be synthesized by means of 'supermatrices', which include the coupled contributions of all the wavenumbers. We introduce reflection and transmission 'supermatrices' in order to eliminate numerical problems arising from loss of precision for evanescent waves in the seismogram synthesis. An interface is assumed to be such that the reflected and transmitted wavefields on its two sides can be represented as purely upgoing and downgoing waves, i.e. the Rayleigh ansatz is imposed. The computational demands of this method can be kept to a minimum by exploiting propagation invariants in the coupled wavenumber domain.
    The superior performance of this 'invariant embedding' approach when compared to propagator or finite difference schemes is illustrated by application to the response of sedimentary basins to excitation by an incident plane wave or a line force. The results are in good general agreement with the other methods, but show greater numberical stability and computational efficiency. In the case of a single interface the 'invariant embedding' procedure for P-SV-waves takes 45 per cent less computation time and 29 per cent less memory than the propagator method of Koketsu (1987a, b). The gains are reduced in a multilayer case because of the level of computation required to calculate the addition rules for the large reflection and transmission supermatrices.

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  • 均質な堆積盆地における地震波動場の最も単純な計算法

    竹中博士

    地震学会講演予稿集   173   1991

  • チリ津波の外洋伝播シミュレーション(共著)

    (財)国際海洋科学技術協会季刊誌Sci.& Tech.   4 ( 1 )   21 - 27   1991

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  • Diffraction of Seismic Waves by Three-dimensional Mountain Topographies

    TAKENAKA Hiroshi, KOKETSU Kozuki

    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN   1991   69 - 69   1991

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    DOI: 10.18940/vsj.1991.2.0_69

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  • Effects of A Magma Chamber on Seismic Waveforms

    Takenaka H., Furumura T., Ohshima H.

    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN   1991   176 - 176   1991

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    DOI: 10.18940/vsj.1991.2.0_176

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  • 3次元不規則成層構造における理論地震記象の高速で安定な計算手法

    竹中博士

    物理探査学会第82回学術講演会講演論文集   47 - 52   1990

  • Computer graphics for the study of transoceanic propagation of tsunamis(共著)

    Proceedings of the 4th Pacific Congress on Marine Science and Technology   1   118 - 123   1990

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  • Diffraction of Elastic Waves by Three Dimensional Mountain Topographies

    Takenaka Hiroshi

    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN   1990   39 - 39   1990

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    DOI: 10.18940/vsj.1990.2.0_39

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  • 41A. Explosion earthquakes of Tokachi Volcano observed by strong motion seismograph.(Abstracts of Papers Presented at the Fall Meeting of the Society)

    Ohshima H., Sasatani T., Takenaka H., Matsushima K., Takagi H., Michiwaki M., Miyakoshi K., Morita T., Nishida Y., Suzuki S., Kasahara M., Okada H.

    Bulletin of the Volcanological Society of Japan. Second series   34 ( 4 )   339 - 340   1989.12

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  • 76B. Change of seismic waveform by magma chamber(Abstracts of Papers Presented at the Fall Meeting of the Society)

    Takenaka H.

    Bulletin of the Volcanological Society of Japan. Second series   34 ( 4 )   377 - 378   1989.12

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  • A41 強震計による十勝岳爆発地震の観測

    大島 弘光, 笹谷 努, 竹中 博士, 松島 健, 高木 朗充, 道脇 正則, 宮腰 研, 森谷 武男, 西田 泰典, 鈴木 貞臣, 笠原 稔, 岡田 広

    日本火山学会講演予稿集   1989   43 - 43   1989

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    Language:Japanese   Publisher:特定非営利活動法人 日本火山学会  

    DOI: 10.18940/vsj.1989.2.0_43

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  • 22P. Geothermal Activity of Usu Volcano since 1977.(Abstracts of Papers Presented at the Spring Meeting of the Society)

    Matsushima N., Takenaka H., Nishida Y.

    Bulletin of the Volcanological Society of Japan. Second series   33 ( 3 )   257 - 257   1988.10

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  • Integration by Fourier transformation and its connection with Integration by linear acceleration method

    TAKENAKA Hiroshi

    Geophysical Bulletin of Hokkaido University   ( 50 )   55 - 61   1988

  • フーリエ変換による積分と線形加速度法による積分との関係

    北海道大学地球物理学研究報告   ( 50 )   55 - 61   1988

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  • P22 1977 年噴火後の有珠山火口原の熱活動について

    松島 喜雄, 竹中 博士, 西田 泰典

    日本火山学会講演予稿集   1988   88 - 88   1988

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    Language:Japanese   Publisher:特定非営利活動法人 日本火山学会  

    DOI: 10.18940/vsj.1988.1.0_88

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  • Strong-Motion Modeling of the 1980 Izu-Hanto-Toho-Oki Earthquake by Inversion Method

    TAKENAKA Hiroshi

    Journal of the Faculty of Science, Hokkaido University. Series 7, Geophysics   8 ( 2 )   109 - 119   1987

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  • Strong-motion modeling of the Izu-Hanto-Toho-Oki earthquake by inversion method

    Journal of the Faculty of Science, Hokkaido University, Series VII (Geophysics)   8 ( 2 )   109 - 119   1987

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  • 東北地方太平洋沖地震震源域の波形トモグラフィー:分解能行列の検討

    岡元太郎, 竹中博士, 中村武史

    S01P-02   1922.10

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Presentations

  • CMT解による観測点補正値を用いた沖縄本島南東沖の地震の震源再決定

    小松正直, 喜多村萌以, 竹中博士

    日本地震学会秋季大会講演予稿集(Web) 2022  2022.10.25 

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    Event date: 2022.10.25

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  • 東北地方太平洋沖地震震源域の波形トモグラフィー:分解能行列の検討

    岡元太郎, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集(Web) 2022  2022.10.24 

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    Event date: 2022.10.24

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  • 海水層および海底地盤構造が海面地震動に与える影響の評価

    中村武史, 竹中博士

    日本地震学会秋季大会講演予稿集(Web) 2022  2022.10.24 

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  • Estimation of subsurface motion from surface seismic records (2): improvement of the method based on the quantitative evaluation

    渡邉禎貢, 竹中博士, 小松正直, 大島光貴

    日本地球惑星科学連合大会予稿集(Web)  2022 

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  • 水平成層構造での海面~海中における水中音響波形計算―海水層による増幅・減幅の影響評価-

    中村武史, 竹中博士

    日本地震学会秋季大会講演予稿集(Web) 2021  2021.10.15 

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    Event date: 2021.10.15

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  • 東北地方太平洋沖地震震源域の波形トモグラフィーに向けた波動場の検討

    岡元太郎, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集(Web) 2021  2021.10.15 

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  • 2016年熊本地震で誘発された大分県中部の地震の初動読み取りと震源決定

    髙崎雄大, 小松正直, 渡邉禎貢, 竹中博士, 大島光貴

    日本地震学会秋季大会講演予稿集(Web) 2021  2021.10.14 

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    Event date: 2021.10.14

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  • 地表観測記録を用いた地中地震動の推定:深い評価点における検討

    渡邉禎貢, 竹中博士, 小松正直, 大島光貴

    日本地球惑星科学連合大会予稿集(Web) 2021  2021.6 

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  • Signal detection by amplitude distribution and Kullback-Leibler divergence

    大島光貴, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2020 

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  • CMT solutions of earthquakes around Okinawa island from strong-motion records by using a land-ocean unified 3D structure model

    小松正直, 小割啓史, 渡邉禎貢, 岡元太郎, 中村武史, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2020 

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  • Initial rupture process of the 2018 Hokkaido Eastern Iburi earthquake inferred from 2D/3D source imagings

    藤本怜, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2020 

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  • Early rupture process of the 2019 Off Yamagata earthquake

    藤本怜, 小割啓史, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2020 

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  • Theoretical analysis of the long-period velocity pulses observed in the 2016 Kumamoto Earthquake Sequence

    垂水洸太郎, 渡邉禎貢, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2020 

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  • Source process of the 14 April 2016 earthquake (M6.5) in Kumamoto area estimated by back-projection analysis

    大島光貴, 竹中博士, 松原誠

    日本地球惑星科学連合大会予稿集(Web)  2020 

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  • CMT solutions of the 2016 central Oita earthquakes using near-field strong motion records

    小割啓史, 小松正直, 竹中博士, 岡元太郎, 中村武史, 吉見雅行, 林田拓己

    日本地球惑星科学連合大会予稿集(Web)  2020 

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  • Estimation of seismic motion at depth from records at a ground surface station without assumption of plane wave incidence

    渡邉禎貢, 竹中博士, 小松正直, 大島光貴, 中村武史

    日本地球惑星科学連合大会予稿集(Web)  2020 

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  • Analytical solution of near-field term, intermediate term, far-filed term, and quasi-static displacement due to rectangular fault in a homogeneous whole space

    垂水洸太郎, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2020 

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  • 3次元不均質構造モデルを用いた2016年大分県由布の誘発地震の余震のCMTインバージョン

    小割啓史, 小松正直, 竹中博士, 岡元太郎, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)  2019 

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  • 地震波形の振幅の確率密度関数を用いたP波・S波到着時刻の読み取りのための最適な階級数の検討

    大島光貴, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2019 

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  • 平面波入射を仮定しないで,地表地震動から地中の入射波を算定する方法

    竹中博士, 小松正直, 渡邉禎貢, 大島光貴, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)  2019 

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  • 南西諸島におけるP波・S波減衰構造

    小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2019 

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  • 東北沖の陸海統合3次元構造モデルに基づく波形トモグラフィーの試み

    岡元太郎, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)  2019 

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  • 岡山県全域の地盤構造の推定

    畝岡歩, 畝岡歩, 小松正直, 藤田高壮, 竹中博士, 西村敬一, 大島光貴, 川瀬博

    日本地震学会秋季大会講演予稿集(CD-ROM)  2019 

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  • ソース・イメージング法を用いた2019年山形県沖の地震における初期段階の破壊過程の推定

    藤本怜, 小割啓史, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2019 

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  • 3次元不均質構造モデルを用いた2016年大分県由布で発生した地震のCMTインバージョン

    小割啓史, 小松正直, 竹中博士, 岡元太郎, 中村武史

    日本地球惑星科学連合大会予稿集(Web)  2018 

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  • 津波の非線形分散波方程式を効率的に解く新スキームの開発

    秦真平, 竹中博士, 小松正直, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)  2018 

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  • 3次元理論地震波形計算によるグリーンランド氷床のQ値の推定

    豊国源知, 竹中博士, 小松正直, 高木涼太, 金尾政紀, 坪井誠司

    日本地震学会秋季大会講演予稿集(CD-ROM)  2018 

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  • スペクトル・インバージョンに基づく岡山県内の強震観測点におけるサイト増幅特性

    畝岡歩, 小松正直, 竹中博士, 大島光貴, 西村敬一, 川瀬博

    日本地震学会秋季大会講演予稿集(CD-ROM)  2018 

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  • 地球の曲率を考慮した3次元構造モデルに基づく地震動・地殻変動・津波統合シミュレーション

    竹中博士, 小松正直, 中村武史, 豊国源知, 岡元太郎

    日本地震学会秋季大会講演予稿集(CD-ROM)  2018 

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  • 南西諸島における震源スケーリング

    小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2018 

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  • 遠地津波のための線形分散波方程式を効率的に解く新しい方法

    秦真平, 竹中博士, 小松正直, 中村武史

    日本地球惑星科学連合大会予稿集(Web)  2018 

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  • 岡山県内の震度観測網,K-NET,KiK-netの観測点におけるサイト増幅特性の抽出

    畝岡歩, 小松正直, 大島光貴, 竹中博士, 西村敬一, 川瀬博

    日本地球惑星科学連合大会予稿集(Web)  2018 

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  • 中小規模の島嶼部における深部地盤S波速度構造モデル(奄美諸島・吐喇列島編)

    山田伸之, 竹中博士, 小松正直

    日本地震工学シンポジウム論文集(CD-ROM)  2018 

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  • 地震波減衰トモグラフィから見る2016年熊本地震震源域下の流体分布

    竹中博士, 小松正直, 小田仁

    日本第四紀学会講演要旨集  2017 

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  • 2次元線形分散津波方程式の効率的な計算:スキーム編

    竹中博士, 秦真平, 小松正直, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)  2017 

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  • 陸海統合3次元構造モデルにもとづく日本海溝の浅い地震のFAMT解析

    岡元太郎, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)  2017 

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  • バックプロジェクション法による2017年熊本地震の破壊過程の推定

    大島光貴, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2017 

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  • 別府湾周辺における微動の連続観測記録を用いた深部地盤構造の検証

    林田拓己, 吉見雅行, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2017 

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  • 南西諸島における連続地動記録を用いた雑微動の相互相関解析

    QIU Dongchen, 小松正直, 豊国源知, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2017 

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  • 強震動計算のための大分県域の3次元速度構造モデル

    吉見雅行, 松山尚典, 鈴木晴彦, 谷田貝淳, 林田拓己, 松島信一, 竹中博士, 三宅弘恵, 竹村恵二

    日本地球惑星科学連合大会予稿集(Web)  2017 

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  • 2016年熊本地震の強震記録を用いた岡山県内のサイト特性の評価

    畝岡歩, 小松正直, 竹中博士, 西村敬一

    日本地球惑星科学連合大会予稿集(Web)  2017 

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  • アレイ解析による2016年4月16日大分誘発地震の震源の推定

    土井原健太, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2017 

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  • S-wavevectorレシーバ関数解析による南西諸島の地震学的構造の推定

    村越匠, 竹中博士, 小松正直, 山田伸之

    日本地球惑星科学連合大会予稿集(Web)  2017 

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  • 地震波干渉法を用いた別府湾周辺地域における深部地盤構造モデルの検証

    林田拓己, 吉見雅行, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2017 

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  • Exploration of S-wave velocity structure of Kita-Daito Island

    2017 

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    Language:Japanese  

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  • 吐か喇(トカラ)列島中之島および宝島の深部地盤S波速度構造

    山田伸之, 竹中博士

    日本地震学会秋季大会講演予稿集(CD-ROM)  2017 

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  • 2次元線形分散津波方程式の効率的な計算:計算編

    秦真平, 竹中博士, 小松正直, 中村武史

    日本地震学会秋季大会講演予稿集(CD-ROM)  2017 

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  • 3次元及び2次元震源イメージングから推定した2014年伊予灘稍深発地震の初期段階の破壊過程

    宇佐美貴政, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2016 

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  • 沖縄本島における深部地盤のS波速度構造

    山田伸之, 竹中博士, 小松正直

    物理探査学会学術講演会講演論文集  2016 

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  • 2016年熊本地震震源域周辺の三次元地震波減衰構造

    小松正直, 小田仁, 竹中博士

    日本地震学会秋季大会講演予稿集  2016 

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  • 2016年熊本地震初期破壊過程のイメージング

    宇佐美貴政, 小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集  2016 

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  • 南西諸島の広帯域地震波形データを用いたS-wavevectorレシーバ関数解析

    村越匠, 竹中博士, 小松正直, 山田伸之

    日本地震学会秋季大会講演予稿集  2016 

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  • 焼きなまし法を用いた初動発震機構解の決定

    小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2016 

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  • グリーンランド地殻浅部の経年的地震波速度変化

    豊国源知, 竹中博士, 高木涼太, 金尾政紀, 坪井誠司, 東野陽子

    日本地震学会秋季大会講演予稿集  2016 

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  • 陸海統合3次元構造モデルにもとづく2016年薩摩半島西方沖地震のシミュレーション

    岡元太郎, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集  2016 

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  • 2015年大分県南部地震(Mj5.7)における大分県周辺の長周期地震動シミュレーションと地下構造モデルの検討

    奥仲達也, 小松正直, 竹中博士, 吉見雅行, 中村武史, 岡元太郎

    日本地球惑星科学連合大会予稿集(Web)  2016 

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  • 南西諸島の広帯域地震波形データを用いたレシーバ関数解析

    村越匠, 竹中博士, 小松正直, 山田伸之

    日本地球惑星科学連合大会予稿集(Web)  2016 

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  • 2014年3月14日伊予灘稍深発地震の初期段階の破壊過程

    齋藤衛, 小松正直, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2015 

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  • 南海トラフにおけるやや長周期地震動の観測とシミュレーションによる再現

    中村武史, 竹中博士, 岡元太郎, 大堀道広, 坪井誠司

    日本地球惑星科学連合大会予稿集(Web)  2015 

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  • 南西諸島における三次元地震波減衰トモグラフィ

    小松正直, 竹中博士

    日本地震学会秋季大会講演予稿集  2015 

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  • 紀伊半島周辺における陸上及び海底地すべりによる波動伝播シミュレーション

    中村武史, 竹中博士, 岡元太郎, 金田義行

    日本地球惑星科学連合大会予稿集(Web)  2015 

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  • グリーンランド氷床モデルを用いた地震波伝播モデリング

    豊国源知, 竹中博士, 金尾政紀, 坪井誠司, 東野陽子

    日本地球惑星科学連合大会予稿集(Web)  2015 

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  • 長大距離地震波動伝播シミュレーションのための地球の曲率を考慮した計算スキーム

    竹中博士, 豊国源知, 中村武史, 小松正直, 岡元太郎

    日本地球惑星科学連合大会予稿集(Web)  2015 

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  • 沖縄島中部から奄美群島南部におけるS波速度構造探査

    山田伸之, 竹中博士

    日本地球惑星科学連合大会予稿集(Web)  2015 

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  • グリーンランド氷床における広帯域連続地震波形記録を用いた地震波干渉法解析

    豊国源知, 竹中博士, 金尾政紀, 坪井誠司, 東野陽子

    日本地震学会秋季大会講演予稿集  2015 

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  • 南海トラフ域における長周期地震動成分の伝播特性と震源メカニズム解析に与える影響の評価

    中村武史, 岡元太郎, 竹中博士

    日本地震学会秋季大会講演予稿集  2015 

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  • 2011年東北地方太平洋沖地震の不均質構造モデルを用いた破壊過程解析(5):相互相関係数による考察

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集  2015 

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  • 八重山・宮古諸島島嶼部における深部地盤のS波速度構造~地下構造モデルの性能評価~

    山田伸之, 竹中博士

    日本地震学会秋季大会講演予稿集  2015 

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  • 大分平野における稠密小半径アレイ微動探査

    吉見雅行, 林田拓己, 松島信一, 川瀬博, 竹中博士, 山田伸之, 徳丸哲義, 杉山長志

    日本地震学会秋季大会講演予稿集  2015 

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  • 沖縄先島諸島におけるP波減衰構造

    小松正直, 竹中博士, 小田仁

    日本地震学会秋季大会講演予稿集  2014 

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  • 不均質構造モデルによる地震波グリーン関数波形を用いた2011年東北地方太平洋沖地震の破壊過程(4)

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集  2014 

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  • 地震波から推定される2011年東北地方太平洋沖地震の破壊過程:不均質構造モデルにもとづくグリーン関数を用いたインバージョン解析

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震工学シンポジウム論文集(CD-ROM)  2014 

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  • 八重山・宮古諸島島嶼部における深部地盤S波速度構造モデル

    山田伸之, 竹中博士

    日本地震学会秋季大会講演予稿集  2014 

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  • 簡便なコーナ周波数fcの推定法と減衰量t*の決定

    小松正直, 竹中博士, 小田仁

    日本地震学会秋季大会講演予稿集  2014 

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  • 月と火星の全球地震波伝播シミュレーション

    豊国 源知, 竹中 博士, 趙 大鵬, 石原 吉明

    SENAC : 東北大学大型計算機センター広報  2013.7  東北大学サイバーサイエンスセンター

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    Language:Japanese  

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  • グリーンランド氷床上での地震波形観測に氷床が与える影響について

    豊国源知, 金尾政紀, 東野陽子, 姫野哲人, 坪井誠司, 竹中博士

    極域科学シンポジウム講演予稿集(CD-ROM)  2013 

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  • 桜島火山におけるACROSS震源位置で励起された弾性波の伝播シミュレーション

    竹中博士, 藤岡慧, 中村武史, 岡元太郎, 宮町宏樹, 八木原寛, 山岡耕春, 國友孝洋, 渡辺俊樹, 井口正人, 為栗健, 三ケ田均, 清水洋

    日本火山学会講演予稿集  2013 

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  • 基盤内S-wavevectorレシーバ関数を用いた九州下の地震学的構造の推定

    上田拓哉, 竹中博士, 村越匠

    物理探査学会学術講演会講演論文集  2013 

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  • 準円筒座標系2.5次元波動モデリング(3)-非弾性減衰-

    豊国源知, 竹中博士, 岡元太郎, ZHAO Dapeng

    日本地震学会秋季大会講演予稿集  2013 

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  • S-wave velocity structure of Fukuoka area

    YAMADA Nobuyuki, TAKENAKA Hiroshi

    2012.11.29 

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    Language:Japanese  

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  • 2011年東北地方太平洋沖地震の破壊過程解析のための3次元近地グリーンテンソル波形計算

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集  2012 

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  • 近地地震における地震動・津波統合3次元数値シミュレーションの新スキーム

    竹中博士, 中村武史, 蔵本稔大, 岡元太郎, 豊国源知

    日本地震学会秋季大会講演予稿集  2012 

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  • 海底地震観測網で観測された地震動の3次元波動伝幡シミュレーションによる再現-構造モデルにおける海水層の導入の重要性

    中村武史, 竹中博士, 岡元太郎, 金田義行

    日本地震学会秋季大会講演予稿集  2012 

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  • 南西諸島における地震動シミュレーションのための三次元地下構造モデルの構築

    藤岡慧, 竹中博士, 山田伸之, 中村武史, 岡元太郎, 村越匠, 藤原広行

    日本地震学会秋季大会講演予稿集  2012 

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  • ACROSSを用いた桜島における能動監視

    宮町宏樹, 八木原寛, 山岡耕春, 渡辺俊樹, 國友孝洋, 井口正人, 為栗健, 三ケ田均, 清水洋, 松島健, 竹中博士

    日本火山学会講演予稿集  2012 

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  • 深井戸観測記録と深部地盤構造モデルを用いたS-wavevectorレシーバ関数解析による関東平野下のプレート構造の推定

    村越匠, 竹中博士

    日本地震学会秋季大会講演予稿集  2012 

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  • モーメントテンソル点震源を用いた準円筒座標系2.5次元波動モデリング

    豊国源知, 竹中博士, 岡元太郎, ZHAO Dapeng, 伊藤喜宏, 長谷川昭

    日本地震学会秋季大会講演予稿集  2012 

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  • 南大東島における地盤震動調査-島の地震動評価のために-

    山田伸之, 立川真太郎, 竹中博士

    日本地震学会秋季大会講演予稿集  2012 

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  • 地中観測網のS-wavevectorレシーバ関数で見る九州の地殻及び最上部マントルの地震学的構造

    上田拓哉, 村越匠, 竹中博士

    日本地震学会秋季大会講演予稿集  2012 

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  • 時間領域差分法による地震波動としての近地地震津波の数値計算

    竹中博士, 藏本稔大, 中村武史, 岡元太郎, 豊国源知

    日本地震学会秋季大会講演予稿集  2011 

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  • 月表面地形・表層構造を考慮した月の地震波伝播モデリング

    岡元太郎, 小林直樹, 竹中博士

    日本惑星科学会秋季講演会予稿集(Web)  2011 

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  • 全地球地震波伝播モデリングを用いた北極における地震波形記録の解釈

    豊国源知, 竹中博士, 金尾政紀

    極域科学・宙空圏・気水圏・生物・地学シンポジウム講演予稿集(CD-ROM)  2011 

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  • アクロスによる桜島火山のマグマ移動検出に向けた能動的アプローチ

    宮町宏樹, 井口正人, 山岡耕春, 渡辺俊樹, 八木原寛, 為栗健, 三ケ田均, 竹中博士, 清水洋

    日本火山学会講演予稿集  2011 

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  • 2011年東北地方太平洋沖地震の破壊過程と近地全波形モデリング

    岡元太郎, 竹中博士, 原辰彦, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集  2011 

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  • 喜界島における微動探査-島の地震動評価のために-

    山田伸之, 竹中博士, 奥平良太

    日本地震学会秋季大会講演予稿集  2011 

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  • 筑紫平野北東部における微動アレイ探査

    奥平良太, 竹中博士, 山田伸之

    日本地震学会秋季大会講演予稿集  2011 

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  • S-wavevectorレシーバ関数解析による関東平野のフィリピン海スラブ・太平洋スラブの形状

    村越匠, 竹中博士

    日本地震学会秋季大会講演予稿集  2011 

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  • 2011年駿河湾で起こった地震における初期段階の震源過程

    後藤史紀, 竹中博士, 中村武史

    日本地震学会秋季大会講演予稿集  2011 

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  • 自己重力の効果を考慮した球座標系2.5次元地震波伝播モデリング(1):カウリング近似

    豊国源知, 竹中博士

    日本地震学会秋季大会講演予稿集  2010 

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  • GPUを用いた地震波伝播シミュレーション(3):地形・流体層と非弾性減衰効果の導入

    岡元太郎, 竹中博士, 中村武史, 青木尊之

    日本地震学会秋季大会講演予稿集  2010 

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  • 先島諸島におけるS波速度構造探査

    山田伸之, 竹中博士, 奥平良太, 後藤史紀, 蔵本稔大

    日本地震学会秋季大会講演予稿集  2010 

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  • 陸上地形・海底地形を考慮した3次元差分法による長周期地震動シミュレーション

    竹中博士, 中村武史, 岡元太郎, 金田義行

    日本地震工学シンポジウム論文集(CD-ROM)  2010 

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  • GPUによる地震波伝播シミュレーション

    岡元太郎, 竹中博士, 中村武史

    情報処理学会シンポジウム論文集  2010 

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  • 福岡県震度計観測点におけるサイト増幅特性の抽出

    大島光貴, 竹中博士, 川瀬博

    日本地震工学シンポジウム論文集(CD-ROM)  2010 

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  • 自己重力を考慮した全地球地震波動場の計算と極域波形データの比較

    豊国源知, 竹中博士, 金尾政紀

    極域科学・宙空圏・気水圏・生物・地学シンポジウム講演予稿集(CD-ROM)  2010 

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  • レシーバー関数解析のための深井戸観測記録の料理法

    竹中博士, 村越匠

    日本地震学会秋季大会講演予稿集  2010 

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  • 3次元不均質構造における平面波斜め入射問題を解く新しい方法:支配方程式と差分法による解法

    竹中博士, 岡元太郎, 中村武史

    日本地震学会秋季大会講演予稿集  2009 

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  • GPGPUを用いた地震波伝播計算の試み

    岡元太郎, 竹中博士

    日本地震学会秋季大会講演予稿集  2009 

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  • 地球中心も含めた精度と効率のよい全地球地震波伝播モデリング

    豊国源知, 竹中博士

    日本地震学会秋季大会講演予稿集  2009 

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  • 2009年8月11日駿河湾で発生した地震の3次元HOT-FDMによる波動伝播シミュレーション

    中村武史, 竹中博士, 岡元太郎, 金田義行

    日本地震学会秋季大会講演予稿集  2009 

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Research Projects

  • 南西諸島における強震動予測の高精度化に向けた海陸統合地下構造モデルの構築

    Grant number:22H01311  2022.04 - 2026.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    竹中 博士, 岡元 太郎, 山田 伸之, 豊国 源知, 中村 武史

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    Authorship:Principal investigator 

    Grant amount:\8840000 ( Direct expense: \6800000 、 Indirect expense:\2040000 )

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  • Full waveform tomography of the 3D structure in and around the source region of the 2011 Tohoku-Oki earthquake

    Grant number:20K04101  2020.04 - 2023.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    岡元 太郎, 竹中 博士

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    Grant amount:\4290000 ( Direct expense: \3300000 、 Indirect expense:\990000 )

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  • 分散性津波方程式の高速な新解法の開発

    2018.04 - 2019.03

    大成学術財団  大成学術財団2018年度研究助成 

    竹中博士, 秦 真平

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    Authorship:Principal investigator 

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  • Study of accuracy of synthetic waveforms and earthquake occurrence site in and around the source area of the 2011 Tohoku-oki earthquake by using a land-ocean unified 3D structure model

    Grant number:16K05535  2016.04 - 2020.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    Okamoto Taro

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    Grant amount:\4550000 ( Direct expense: \3500000 、 Indirect expense:\1050000 )

    We evaluate the accuracy of synthetic waveforms for small earthquakes in the source area of the 2011 Tohoku-Oki earthquake (MJMA 9.0) at the Japan Trench. We compute the synthetic waveforms on the basis of a land-ocean unified 3D structure model using our HOT-FDM. In estimating the source parameters, we apply FAMT method that we have recently proposed. We find that the FAMT solutions for events with shallow-angle thrusting mechanisms are located near the plate interface, which demonstrates the importance of using a 3D model. We find that the full waveforms with periods shorter than about 10 s are not well reproduced. At periods around 4 s, the initial body waveforms can be modeled, but the later surface waves are difficult to reproduce correctly. We further examine the 3D sensitivity kernels: for short-period wavefield (below around 10 s) we observe a curved pattern which cannot be predicted by 1D earth models. This indicates the effects of 3D heterogeneity.

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  • Studies on prediction of strong ground motion and tsunamis for islands

    Grant number:26282105  2014.04 - 2018.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    TAKENAKA Hiroshi, MURAKOSHI Takumi, KOMATSU Masanao

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    Grant amount:\14950000 ( Direct expense: \11500000 、 Indirect expense:\3450000 )

    We have studied three main subjects on prediction of strong ground motion and tsunamis for the Ryukyu Islands as typical examples of islands in Japan. First, we have improved the subsurface structure models including near-surface layers. Secondly, we have implemented an integrated system to continuously simulate seismic motion, quasi-static crustal deformation and tsunami due to a sub-oceanic earthquake, and confirmed the stable performance by applying it to a number of past events which occurred around the Ryukyu Islands. Thirdly, we have realized a precise hypocenter location system based on "waveform relocation technique" which combines a teleseismic inversion of source parameters with a grid search procedure to correct possible systematic bias in hypocentral parameters using 2.5-D Green's functions for a 2-D slice from the realistic 3-D heterogeneous structure model. We have also demonstrated the effectiveness of this system by applying it to middle-sized events.

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  • Rupture Process of The 2011 Tohoku-Oki Earthquake: Analysis by using Green's Tensor Waveforms

    Grant number:24540452  2012.04 - 2015.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    OKAMOTO Taro, TAKENAKA Hiroshi, SUGIOKA Hiroko

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    Grant amount:\4940000 ( Direct expense: \3800000 、 Indirect expense:\1140000 )

    We analyzed "seismic" rupture process of the March 11, 2011 Tohoku-Oki earthquake (GCMT Mw9.1) by using a non-linear multi-time-window waveform inversion analysis. We used Green's tensor waveforms computed for laterally heterogeneous structure models: full 3D model was used for strong-motion Green's tensor waveforms, and 2.5D structure models were used for teleseismic P-wave Green's functions. The inferred slip distribution was characterized by large slips near the hypocenter with maximum slip of about 37 m. The near-trench slips were inferred to be relatively small. An isolated slip region was also identified at deep beneath the coast of Fukushima prefecture. On the other hand, large amount of "artificial" slips were inferred close to the trench when we apply 1D Green's functions that did not incorporate the effect of realistic lateral heterogeneity. Our result suggests the trench-ward large deformation that caused large tsunamis did not radiated strong seismic waves.

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  • Strong-motion prediction for islands

    Grant number:23310122  2011.04 - 2014.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    TAKENAKA Hiroshi, OKAMOTO Taro, YAMADA Nobuyuki, YAMADA Nobuyuki, TOYOKUNI Genti, MURAKOSHI Takumi, FUJIOKA Akira, UEDA Takuya

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    Grant amount:\14040000 ( Direct expense: \10800000 、 Indirect expense:\3240000 )

    Japan consists of many islands. From the point of view of disaster prevention, it is also important to improve the precision of strong ground motion prediction for the islands. The Ryukyu Islands are a typical example of such islands. In this study we build a 3D numerical structure model for modeling of strong ground motion, which includes land and ocean-bottom topographies and a seawater layer as well as subsurface structures of the arc side and the PHS slab, partially based on the existing models for near-surface structure and a slab-top depth of the PHS. We then try to improve the near-surface structure model in the islands using the microtremor surveys we conducted originally in this project. We then simulate seismic wave propagation for three sub-oceanic earthquakes which occurred near the Amami Islands, Okinawa Island and Miyako Island to confirm the applicability of the constructed structure model.

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  • Study of detection of dynamic change of magma transport process by using ACROSS and its cause, in Sakurajima volcano

    Grant number:23340130  2011.04 - 2014.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    MIYAMACHI Hiroki, YAMAOKA Koshun, WATANABE Toshiki, IGUCHI Masato, TAMEGURI Takeshi, MIKADA Hitoshi, YAKIWARA Hiroshi, SHIMIZU Hiroshi, TAKENAKA Hiroshi

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    Grant amount:\20930000 ( Direct expense: \16100000 、 Indirect expense:\4830000 )

    In order to monitor quantitatively magma transport process in Sakurajima volcano, the ACROSS system composed of two vibration sources was deployed in Sakurajima Island, and the system produced continuously the accurately controlled imperceptible elastic wave signal from 5 to 15 Hz. The signal from the ACROSS is routinely monitored by 15 permanent stations and 4 temporal stations in Sakurajima volcano. We successfully observed the ACROSS signal at each station and could detect temporal variation of the transfer function (TF). Because the temporal variation of later phases in the TF was obviously larger than that in the early phases, we inferred that the temporal variation of the later phases reflected the temporal change of the structure in deep regions beneath Sakurajima volcano. We also found that the temporal variation of the TF is correlated with volcanic activity such as the daily volcanic eruptions and crustal deformation in Sakurajima Island.

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  • Comprehensive Research on Long-Period Ground Motion and Urban Disaster Mitigation

    Grant number:19201034  2007 - 2010

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)  Grant-in-Aid for Scientific Research (A)

    KOKETSU Kazuki, HORI Muneo, MIYAKE Hiroe, IRIKURA Kojiro, KUDO Kazuyoshi, MIDORIKAWA Saburoh, TAKAI Nobuo, IWATA Tomotaka, KAEWASE Hiroshi, KAMAE Katsuhiro, TAKENAKA Hiroshi, HISADA Yoshiaki, AOI Shin, FURUMURA Takashi, SASATANI Tsutomu, SEKIGUCHI Haruko, FUKUWA Nobuo, ZAMA Shinsaku, FUJIWARA Hiroyuki, HIGASHI Sadanori

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    Grant amount:\46020000 ( Direct expense: \35400000 、 Indirect expense:\10620000 )

    Toward seismic hazard assessment for long-period ground motion, this study integrates four research components of seismic source, velocity structure, numerical simulation, and damage and risk. We then create the Japan Integrated Velocity Structure Model, and long-period ground motion hazard and risk maps.

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  • Direct estimation of deep subsurface material properties from teleseismic waveforms : Transmission AVO

    Grant number:19540448  2007 - 2009

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    TAKENAKA Hiroshi, OKAMOTO Taro, MURAKOSHI Takumi, JAFARGANDOMI Arash

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    Grant amount:\4550000 ( Direct expense: \3500000 、 Indirect expense:\1050000 )

    遠地地震の波形記録を用いて地球内部の速度不連続面をマッピングし,その物性値としての地震波速度を抽出する新しい手法の実現へ向けて,最も重要な遠地実体波波形の数値シミュレーションに関わる4課題:(1)非弾性減衰の導入,(2)3次元不均質構造の平面波応答計算,(3)計算精度の向上,(4)計算の高速化に取組み,それぞれの解決策となる新しい手法を提案した。

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  • Earthquake Damage Prediction in Fukuoka Area due to Kego Fault and its Environmental and Economic Impact Evaluation

    Grant number:18310125  2006 - 2008

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    KAWASE Hiroshi, SEIKE Tadashi, TAKENAKA Hiroshi, YAMADA Nobuyuki, MURAKAMI Hitomi, TAKAGUCHI Hiroto, FUJITA Toshiyuki, MATSUSHIMA Shinichi, NARAN Mandora

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    Grant amount:\17500000 ( Direct expense: \14500000 、 Indirect expense:\3000000 )

    まず福岡市域の各観測点に対して、地震基盤から表層までの増幅特性を求め理論特性と比較検証した。また、人的被害予測モデル構築のために、「閉じ込め」確率予測式を求め、死傷者の分布などを推定した。さらに、城南区で微動観測を実施して、三次元盆地構造モデルを改良した。一方、微動の水平上下スペクトル比から断層位置を特定する方法を警固断層に適用し、その有効性を検証した。最後に整備した計算機によって三次元FDM計算を行い、警固断層地震の強震動予測を実施した。さらに福岡市の構造物の振動特性に基づいて被害予測モデルを補正して高精度化した。以上のシステム開発により、当初目標を達成できた。

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  • Source location and slip distribution of the subduction zone earthquakes

    Grant number:18540418  2006 - 2008

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    OKAMOTO Taro, TAKENAKA Hiroshi

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    Grant amount:\3700000 ( Direct expense: \3400000 、 Indirect expense:\300000 )

    沈み込み帯の地震からの遠地実体波波形には震源付近の不均質構造に起因する強い後続波が現れるため、地震の詳細な解析が困難になる場合がある。本研究では不均質構造のもとでの波動計算を非常に効率良く実行できる独自の手法によって理論波形を計算し、小規模地震の地震発生場所・発震機構解を推定する手法と、大規模地震の断層すべり分布を決定する手法とを開発した。これらの手法を2006年ジャワ津波地震と2007年南スマトラ地震とに適用して、震源域の不均質構造と地震発生場所や断層すべり分布との関係を詳しく考察した

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  • エジプト・ナイル川流域都市における地震動予測

    Grant number:04F04319  2004 - 2006

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    竹中 博士, MOUSTAFA Sayed S.R., MOUSTAFA Sayed S.K.

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    Grant amount:\2400000 ( Direct expense: \2400000 )

    地中海東部一帯では3つのプレートが会合しており,地震活動が極めて活発な地域に当たる.地中海の北部一帯に比べるとエジプト国内の地震活動度は高いとはいえないが,紅海,シナイ半島近傍及びナイル川流域には規模の大きな地震が発生している.エジプトの国土は日本の約2.3倍の面積があるが大部分は砂漠が占め,主な居住区はナイル川流域の3パーセントに過ぎない.そのため人口の超過密な地域が存在する.またこの地には人類全体の遺産とも言うべき古代エジプトの遺跡が数多く存在する.本研究の目的は,このような地域の地震災害軽減をめざして,ナイル川流域の大地震を想定した強震動予測を行うことである.平成18年度本研究の最終年度であり,特別研究員期間終了までの7ヶ月半で以下の項目を実施した.
    (1)地震動シミュレーションのため,1992年カイロ地震の震源とカイロ全域を含む広域にわたる領域について3次元不均質構造モデルを構築した.これは,地形,地球物理学的及び地質学的データから推定された表層基盤面分布,モホ面の深度分布等の広域データ及びカイロ周辺のより詳しい表層地盤構造の情報を基に作成した3次元不規則成層構造(層内均質)モデルである.
    (2)それを基に1992年カイロ地震時のカイロ周辺の長周期地震動(地動速度)を3次元数値シミュレーション手法(spectral element method)を用いて求めた.その結果を基に,1992年カイロ地震の震源断層の延長上に推定されている伏在断層で想定される地震における地震動に性状について考察した
    (3)また,収集した表層地盤情報を基にナイル流域のカイロ南西域における液状化の可能性について検討した.

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  • Ultra Efficient Methods of Seismic Wave Modeling for Waveform Tomography

    Grant number:16540389  2004 - 2005

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    TAKENAKA Hiroshi

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    Grant amount:\3600000 ( Direct expense: \3600000 )

    Waveform tomography is one of the highest resolution methods for imaging the Earth's interior. Application of the waveform tomography to real data requires huge number of computations of 3D seismic wavefields. For such iterative calculations of synthetic seismograms with limited computer resources, a fast and accurate modeling method is needed. For this purpose, we developed the following efficient numerical methods for modeling seismic waveforms :
    1. Quasi-spherical approach for seismic wave propagation in a 2D slice through a global earth model with lateral heterogeneity : The elastodynamic equation for spherical coordinates is not solved in the conventional spherical domain but instead in a "quasi-spherical domain" using the finite-difference method (FDM). This approach can correctly model 3D geometrical spreading effects with computational times and memories comparable to 2D methods, and can treat asymmetric structure about the vertical axis including the source.
    2. Axisymmetric modeling : It can also correctly model geometrical spreading effects in 3-D within computational resources comparable to 2-D modeling. However, in the previous works with the axisymmetric modeling, seismic sources were restricted to axisymmetric sources such as an explosive source. In this study, we proposed an implementation of an arbitrary moment tensor point source to axisymmetric modeling using the FDM.
    3. Efficient FDM algorithm for modeling seismic plane waves for vertically heterogeneous "viscoelastic" media : It can model frequency-dependent anelastic (Q) effects. The scheme uses a 1D grid, which causes a significant reduction in computation time and memory requirement compared to the corresponding 2D or 3D computations.

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  • Ultra efficient methods for modelling waveforms in seismic surveys

    Grant number:13640425  2001 - 2002

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    TAKENAKA Hiroshi

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    Grant amount:\1600000 ( Direct expense: \1600000 )

    In this study we developed efficient numerical methods for modeling seismic waveforms in seismic exploration.
    In the first year we developed a very efficient procedure to calculate plane-wave responses of arbitrary 1-D media, such as gradient velocity or randomly heterogeneous structures, using the finite-difference method in the time domain (FDTD). This may be useful for analysis of reflection survey or seismic logging data.
    In the second year we developed an ultra efficient method for modeling seismic waveforms in refraction or wide-angle reflection surveys. The most common form of seismic exploration remains a nearly linear survey with data acquisition lines including the source and receivers. For this situation we developed a 2.5-D modeling method for the simulation of 3-D seismic wavefields in media varying in two dimensions. The computer memory requirements and computation time are only slightly larger than those for 2D computations. We demonstrated the validity and efficiency of the technique with numerical examples, including a profile across a realistic model of subduction zone structure.

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  • Study on the Mantle-Upwelling Structure of Non Island-Arc Type West off Kyushu

    Grant number:10304034  1998 - 2000

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A).  Grant-in-Aid for Scientific Research (A).

    SUZUKI Sadaomi, TAKENAKA Hiroshi, SHIMIZU Hiroshi, NAKADA Masao, SHINOHARA Masanao, KAME Nobuki

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    Grant amount:\30200000 ( Direct expense: \30200000 )

    The Okinawa trough which is considered to be in an early stage of backarc spreading locates in the backarc region of Ryukyu-Kyushu arc. Understanding mechanism of backarc spreading and backarc volcanism of Kyushu, we conducted an explosion seismology in the northeastern Okinawa trough west off Kyushu by using ocean bottom seismographs (OBSs) in fall of 1999. Twenty OBSs were deployed at intervals of 15 km in the NNE-SSW seismic profile of 300 km in length along the trough center. We used airguns and 76 explosives as controlled sources. During shooting of the airguns, reflection waves were recorded by 24-ch hydrophone streamer towed from the shooting ship. An obtained seismic reflection profile shows large lateral heterogeneity in the upper crust in spite of smooth seafloor topography of the surveyed area. On the distance-time sections of OBSs, apparent velocities of first arrivals vary due to the heterogeneity. The sedimentary section consists of two layers. The upper sedimentary layer has a thickness of 200-500m with P-wave velocity (Vp) of 1.7 - 1.9 km/s. A vertical velocity gradient of the upper layer is small. The lower sedimentary layer has Vp of 2.0 - 3.5 km/s with relatively large vertical velocity gradient. The thickness of the lower layer has large variety from 800 m to 3500m. The upper crust has large lateral heterogeneity and is also divided into two layers. Vp at the top of the uper crust vary in 3.0 - 4.9 km/s. The lower layer of the upper crust has Vp of 5.6 - 6.0 km/s. The thickness of the upper crust changes from 3 km to 9 km. The boundary between the upper and lower crust is about 10 km in depth below the sea surface. The lower crust has Vp of 6.5 - 6.7 km/s. Compared with the upper crust, the lower crust is relatively homogeneous. A thickness of the lower crust is about 15 km. The crust has a thickness of about 25 km in total and the Pn velocity is estimated to be 7.7 -7.8 km/s. The distribution of Vp and the thickness of the crust indicated that the crust of the northeastern Okinawa trough is similar to that of island arc than to that of ocean. It is suggested from the obtained seismic structure that the northeastern Okinawa trough is in the incipient stage of the back-arc rifting.

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  • 海溝型地震の高精度震源過程イメージング

    Grant number:09740357  1997 - 1998

    日本学術振興会  科学研究費助成事業 奨励研究(A)  奨励研究(A)

    竹中 博士

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    Grant amount:\1800000 ( Direct expense: \1800000 )

    我国で起きる巨大地震のほとんどは海溝付近を震源としており,海溝付近で起きた中規模以上の地震の震源過程をできるだけ詳細に精度良く調べることは,地球科学的側面からも防災的側面からも非常に重要である.現在稼働しているグローバル広帯域地震観測点の数は多く,通常,震源を囲む全方位の遠地波形記録を得ることが可能である.したがって,これらの記録を解析することにより震源過程を精度良く推定できることが期待される.本研究課題の目的は,これら遠地波形記録を用いて震源過程を推定する手法の大幅な改善を図り,海溝型地震の高精度かつ高分解能の震源過程推定を実現することである.
    2年間の研究期間の内,初年度である昨年度は,震源過程推定にとって最も重要な「理論地震記象」の研究を行った.その結果高精度かつ効率的な遠地地震波形計算法の開発を行うことができた.具体的には2次元的に不均質な構造における3次元地震波動場を時間領域で計算する高精度かつ効率的な2.5次元差分法スキームを開発し,計算コードを作成した.理論記象の精度が上がると,震源過程推定の精度だけでなく分解能も向上させることができる.そこで,今年度は,昨年度開発した理論地震記象計算法を適用した震源過程のイメージング手法の開発を行った.具体的には震源過程の表現には運動学的定式化を採用し,モーメント密度テンソルの時空間分布関数を推定する.定式の離散化は,問題の線形性を崩さない形で行った.推定には,勾配法に基づくイメージング技法を適用した.

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  • Strong Motion Estimation for Active Faults with High Earthquake Potential

    Grant number:08248111  1996 - 1999

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas  Grant-in-Aid for Scientific Research on Priority Areas

    IRIKURA Kojiro, KUDO Kazuyoshi, IWATA Tomotaka, OKADA Atsumasa, TAKENAKA Hiroshi, KAMAE Katsuhiro

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    Grant amount:\107500000 ( Direct expense: \107500000 )

    Our major objectives are to obtain accurate long-term earthquake prediction by assessing hazard potential of active faults, to clarify physics of the faulting dynamics and to develop the numerical as well as semi-empirical methods for precise ground-motion modeling by computational and observational approaches. Final target is to establish the methodology of predicting strong ground motions for hypothetical active-fault earthquakes and to mitigate earthquake damage from future large earthquakes.
    We have been developing the above six subjects as follows : (1) Aerial photograph interpretation and paleoseismic trenching were made to date late Holocene earthquakes along the active faults for the seismic hazard evaluation on the Median Tectonic active fault system (MTL). The geometry and average slip rate of seismic source faults were obtained using the analysis of balanced cross sections based on seismic reflection profilings and boring data in some representative areas, Shinjo and Tomakomai. Fault branching and directivity of rupture propagation were studied from rupture patterns of recent earthquake faultings. (2) The arresting mechanism of dynamic crack growth was studied by BIEM and compared with surface geometry of active faults. Strong pulses near the earthquake faults were calculated by near-field expression theory with a dynamic slip-rate time function. Source heterogeneity was studied by combining the results of low-frequency waveform and high frequency envelope inversions using strong ground motion and broadband recordings. Source characterizations of inland crustal earthquakes and large intra-plate earthquake were done using high-quality network data. (3) Accurate 3-D modelings of underground structures are done by joint inversion of refraction and gravity data. Site effects for sedimentary basins and shallow soil layers are well estimated from S-wave profiles derived by microtrmor array measurements, validated by direct evaluations of amplifications from earthquake records. (4) Numerical methods for propagation media with irregular interfaces are developed as a hybrid scheme with the indirect boundary element method and semi-analytical solution for flat interfaces. Seismic anisotropy are confirmed by some observation and numerical simulation in the source region of the 1997 Kagosima-hokuseibu earthquakes. (5) The results of refraction, reflection, and gravity surveys were gathered for deriving the three-dimensional underground structure in the Kobe-Hanshin area. Simulations of strong ground motions in and around heavily-damaged areas were done for examining the relation between strong ground motions and structure damage. Ground motion estimations considering source effects as well as seismic responses due to complex structures in both macro and micro scales were studied in observation and numerical techniques for the subduction and slab earthquakes. (6) Methods of strong motion prediction for future large earthquakes were developed and validated by comparing synthesized results with the observed data and damage distribution during the 1995 Hyogo-ken Nanbu and the 1994 Northridge earthquakes. Estimation of strong ground motions during the 1948 Fukui earthquake was done by hybrid simulation method. The source characterization for large inland earthquakes has been studied from statistical analyses of slip distributions with the waveform inversion.
    The results of the above six topics was combined to establish the methodology of estimating strong ground motions for hypothetical active-fault earthquakes. We summarize the procedure that is currently used to characterize earthquake rupture models, based on geological investigations of capable earthquake faults and seismological studies of source models. Then we propose a recipe of predicting strong ground motion form scenario earthquakes caused by active faults.

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  • 火山体の構造が地震波形に及ぼす影響の理論的研究

    Grant number:06740363  1994

    日本学術振興会  科学研究費助成事業 奨励研究(A)  奨励研究(A)

    竹中 博士

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    Grant amount:\1100000 ( Direct expense: \1100000 )

    本研究では、火山体の構造の内、重要と考えられる3種類の不均質(火山地形、低速度貫入物、不規則成層)が地震波形に与える影響について調べるために、数値シミュレーション及び、そのための波動計算法の改良を行った。
    まず、地形の効果を取り扱った。火山地形の2次元性及び3次元性が地震波形に及ぼす影響を調べた。2次元性については近地の波形(近地問題)、3次元性については遠地の波形(遠地問題)を対象とした。計算法は、2.5次元境界積分方程式法並びに3次元reflectivity法を用いた。
    次に、マグマ溜りやダイクといった低速度の貫入物が地震波形に及ぼす影響を調べた。ここでも近地問題と遠地問題の両方を解析した。計算は、2次元reflectivity及び2次元Pseudospectral法を用いて行った。Pseudospectral法の計算結果はアニメーションにし、貫入物によって地震波が散乱する過程を視覚的に追跡する試みを行った。
    最後に、火山体中の層構造(不規則成層構造)における地震波の伝播過程を調べた。計算には、2次元Pseudospectral法並びに3次元reflectivity法を用い、特にカルデラの堆積層の2次元的及び3次元的影響について解析した。ここでは遠地問題だけを扱った。その際用いたPseudospectral法には、今回、解く問題の空間対称性を利用して計算量を大幅に減らす工夫を施した。この計算法については、定式化並びに計算例を地震学会秋季大会(福岡)で発表した。
    実際の火山では、これら3種類の不均質の間に相互作用があるわけであるが、まず波動伝播の素過程を明らかにするという意味から、今回は、特に、研究対象をこれらの個々の影響に絞ることにした。3種類の不均質の間の相互作用については、今後の課題である。

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  • Cooperative Research for Strong Ground Motion Prediction

    Grant number:05302069  1993 - 1995

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Co-operative Research (A)  Grant-in-Aid for Co-operative Research (A)

    IRIKURA Kojiro, TAKENAKA Hiroshi, YOKOI Toshiaki, KUDO Kazuyoshi, SASATANI Tsutomu, IWATA Tomotaka

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    Grant amount:\10400000 ( Direct expense: \10400000 )

    The purposes of this cooperative research project are (1) to compare and evaluate usual prediction methods of strong ground motions for future large earthquakes in the points of Applied seismology and Engineering Seismology and (2) to find and establish more accurate estimation method of strong ground motions. Our study period was from 1993 to 1995. During this period, we had a variety of earthquake disasters by the 1993 Kushiro-Oki, Hokkaido-Nansei-Oki, the 1994 Hokkaido-Toho-Oki, Sanriku-Haruka-Oki, and the 1995 Hyogoken-nanbu earthquakes. Members of this research group carried the cooperative strong motion observations and/or analyzes. Especially, our group members tried to investigate the cause of the Great Hanshin-Awaji earthquake disaster by empirical, semi-empirical, and theoretical approaches and elucidated quantitatively. On Jan., 1996, the symposium on prediction of strong ground motions was held with not only our group members but foreign researchers. Moreover, we made a report on Cooperative Research for Strong Ground Motion Prediction.

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  • Seismology, Earthquake engineering

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    Grant type:Competitive

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  • 地球物理学,地震学, 地震工学,地震防災

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    Grant type:Competitive

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