HR: 1340h
AN: S13D-1088    [Abstracts]
TI: 3D Structural Model in Northwestern Kagoshima, Japan, for Strong Motion Simulation
AU: Takenaka, H
EM: takenaka@geo.kyushu-u.ac.jp
AF: Dept. Earth & Planet. Sci., Fac. Sci., Kyushu Univ., 6-10-1 Hakozaki, Fukuoka, 812-8581 Japan
AU: * Fujii, Y
EM: fujii@cc.kyushu-u.ac.jp
AF: Computing & Communications Center, Kyushu Univ., 6-10-1 Hakozaki, Fukuoka, 812-8581 Japan
AU: Miyamachi, H
EM: miya@sci.kagoshima-u.ac.jp
AF: Earth & Environmental Sci., Fac. Sci., Kagohima Univ., 1-21-35 Korimoto, Kagoshima, 890-0065 Japan
AB: Nowadays the dramatic development of computer resources and computational techniques have allowed us to calculate the seismic wavefields of three-dimensionally heterogeneous structure models (3D models). Using the 3D models, seismic-wavefield simulations have been widely performed in order to estimate strong motion or to calculate the Green functions for source inversions. Therefore, the construction of realistic 3D models is the key to success for strong motion predictions or source inversions. The purpose of this study is to construct a 3D model which has a adequate ability for strong motion simulation. We construct a 3D model in northwestern Kagoshima region of Kyushu island, Japan using all kinds of geophysical and geological data which were well investigated in the study area. The 3D model consists of six layers with width of 80 km, length of 80 km and depth of 40 km. When we construct the 3D model, we estimate a depth for a top of each layer and next assigned $P$-wave velocity to the top and its gradient for each layer. Using the constructed 3D model we then simulate the seismic waveforms of two small earthquakes (M4.6, M3.6) by the finite difference method to assess the ability of the 3D model for seismic motion simulation with frequency range between 0.1 to 1 Hz. These test events are aftershocks of the 1997 Northwestern Kagoshima, Japan, earthquakes, which were well recorded at K-NET (NIED) stations and our stations located on near-field hard rock sites. As the results, it can then be seen that the good agreement of $P$ and $S$ waves between the synthetic and the observed waveforms. It suggests that our 3D model is suitable to seismic wavefield simulations in the frequency range. We also compare the synthetic waveforms calculated by using the 3D structural model and those from the corresponding 1D model, and found that 1D synthetics can poorly explain the observed waveforms as compared to the 3D ones, which may suggest that the constructed 3D model can be applied to the strong motion simulations or source inversions using the 3D Green functions for large events occurring in this region, such as the mainshocks of the 1997 Northwestern Kagoshima earthquakes ($M$6.5, $M$6.3).
DE: 7212 Earthquake ground motions and engineering
SC: Seismology [S]
MN: 2004 AGU Fall Meeting