Faculty Profiles - TAKENAKA Hiroshi

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

Language：English Publisher：AMER GEOPHYSICAL UNION

DOI： 10.1029/1999GL008385

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

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

Zisin 53 ( 2 ) 185 - 192 2000

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

53 ( 4 ) 294 - 308 2000

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

Hiroshi Takenaka

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

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

Scopus

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

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

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

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

Language：English Publisher：TERRA SCIENTIFIC PUBL CO

DOI： 10.5636/eps.52.13

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

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

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

Language：English Publisher：TERRA SCIENTIFIC PUBL CO

DOI： 10.5636/eps.52.3

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

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

21 ( 1 ) 9 - 18 2000

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

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

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

H Takenaka

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

Language：English Publishing type：Rapid communication, short report, research note, etc. (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

DOI： 10.5636/eps.52.299

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

Language：English Publisher：BLACKWELL SCIENCE LTD

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

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

Language：English Publisher：BLACKWELL SCIENCE LTD

DOI： 10.1046/j.1365-246x.1999.00959.x