MISC - TAKENAKA Hiroshi

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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Language：English   Publisher：SEISMOLOGICAL SOC AMER  

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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Language：English   Publisher：OXFORD UNIV PRESS  

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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Language：English   Publisher：OXFORD UNIV PRESS  

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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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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Language：English   Publisher：SEISMOLOGICAL SOC AMER  

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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Language：English   Publisher：BLACKWELL SCIENCE LTD  

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.

DOI： 10.1111/j.1365-246X.1996.tb05635.x

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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.

DOI： 10.1111/j.1365-246X.1996.tb05640.x

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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.

DOI： 10.1111/j.1365-246X.1996.tb05640.x

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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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Language：English   Publisher：BLACKWELL SCIENCE LTD  

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.

DOI： 10.1111/j.1365-246X.1996.tb05635.x

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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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Language：Japanese   Publisher：SEISMOLOGICAL SOCIETY OF JAPAN  

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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Language：Japanese   Publisher：SEISMOLOGICAL SOCIETY OF JAPAN  

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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Language：English   Publisher：CENTER ACADEMIC PUBL JAPAN  

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.

DOI： 10.4294/jpe1952.44.529

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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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Language：English   Publisher：CENTER ACADEMIC PUBL JAPAN  

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.

DOI： 10.4294/jpe1952.44.529

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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

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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

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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

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