Faculty Profiles - TAKENAKA Hiroshi

MISC - TAKENAKA Hiroshi

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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

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

Language：English Publisher：TERRA SCIENTIFIC PUBL CO

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

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

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

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

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

Language：English Publisher：TERRA SCIENTIFIC PUBL CO

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.

DOI： 10.5636/eps.53.149

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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

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

Language：English

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

Language：English Publisher：TERRA SCIENTIFIC PUBL CO

DOI： 10.5636/eps.53.149

Web of Science

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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

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

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

Language：Japanese Publisher：SEISMOLOGICAL SOCIETY OF JAPAN

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

Language：English

DOI： 10.1046/j.1365-246X.2001.01413.x

Scopus

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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