HR: 0800h
AN: S11A-0276    [Abstracts]
TI: Diffraction of seismic waves from 3-D canyons and alluvial basins modeled using the Fast Multipole-accelerated BEM
AU: * Chaillat, S
EM: chaillat@lms.polytechnique.fr
AF: Laboratoire de M\'ecanique des Solides, École Polytechnique, Palaiseau Cedex, 91128, France
AU: * Chaillat, S
EM: chaillat@lms.polytechnique.fr
AF: Universit\'e Paris-Est, Laboratoire Central des Ponts et Chauss\'ees, 58 bd Lefebvre, Paris, 75015, France
AU: Bonnet, M
EM: bonnet@lms.polytechnique.fr
AF: Laboratoire de M\'ecanique des Solides, École Polytechnique, Palaiseau Cedex, 91128, France
AU: Semblat, J
EM: semblat@lcpc.fr
AF: Universit\'e Paris-Est, Laboratoire Central des Ponts et Chauss\'ees, 58 bd Lefebvre, Paris, 75015, France
AB: Seismic wave propagation and amplification in complex media is a major issue in the field of seismology. To compute seismic wave propagation in complex geological structures such as in alluvial basins, various numerical methods have been proposed. The main advantage of the Boundary Element Method (BEM) is that only the domain boundaries (and possibly interfaces) are discretized, leading to a reduction of the number of degrees of freedom. The main drawback of the standard BEM is that the governing matrix is full and non- symmetric, which gives rise to high computational and memory costs. In other areas where the BEM is used (electromagnetism, acoustics,…), considerable speedup of solution time and decrease of memory requirements have been achieved through the development, over the last decade, of the Fast Multipole Method (FMM). The goal of the FMM is to speed up the matrix-vector product computation needed at each iteration of the GMRES iterative solver. Moreover, the governing matrix is never explicitly formed, which leads to a storage requirement well below the memory necessary for holding the complete matrix. The FMM-accelerated BEM therefore achieves substantial savings in both CPU time and memory. In this work, the FMM is extended to the 3-D frequency-domain elastodynamics and applied to the computation of seismic wave propagation in 3-D. The efficiency of the present FMM-BEM is demonstrated on seismology- oriented examples. First, the diffraction of a plane wave or a point source by a 3-D canyon is studied. The influence of the size of the meshed part of the free surface is studied, and computations are performed for non- dimensional frequencies higher than those considered in other studies (thanks to the use of the FM-BEM), with which comparisons are made whenever possible. The method is also applied to analyze the diffraction of a plane wave or a point source by a 3-D alluvial basin. A parametrical study is performed on the effect of the shape of the basin and the interaction of the wavefield with the basin edges is analyzed.
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting