HR: 0800h
AN: S41A-0957    [Abstracts]
TI: Source Images of the 1997 Kagoshima Earthquakes With High Resolution Using the Grid Representation and 3D Heterogeneous Green Functions
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: 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: 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: The seismic wavefield is strongly affected by the underground structure through which the seismic waves propagate from source to observation stations. However, in most of conventional source inversions, horizontally layered media (one-dimensional structure) have been used for calculation of the Green functions. The purpose of this study is to obtain the high accuracy and high resolution images of source processes using the 3D Green functions which include more realistic wave propagation effects. We investigate two mainshocks of the 1997 Northwestern Kagoshima, Japan, earthquakes (the first mainshock:$M$6.5, the second mainshock:$M$6.3), which are well recorded at near-source strong motion stations of the K-NET. We have developed a parallel computation code of the finite-difference method (FDM) to calculate the 3D Green functions using the reciprocity theorem, which effectively reduces the the number of computation times. We use a realistic 3D structure model for the northwestern Kagoshima region constructed by Fujii et al. (2004) for the FDM calculations of the 3D Green functions. A new inversion method (Takenaka and Fujii, 2003 AGU Fall Meeting) by a grid model approach is applied to the 0.1-1Hz bandpass filtered displacement waveforms. As the results, it is found that for the first mainshock, the rupture began from the hypocenter and propagated mainly toward the shallower western part and the deeper eastern part. The maximum amplitude of slip velocity is more than about 4km/s. The locations of asperities are extremely consistent with the areas where the aftershocks are not abundant. The comparison of the inversion result with the velocity perturbation of the seismic tomography (Miyamachi et al., 1999) indicates that the rupture propagated to the high velocity zone and stopped there. Also for the second mainshock, the slip distribution was obtained with high accuracy and high resolution, which considerably overlaps on the low activity zone of the aftershocks. The inversion results inferred using the conventional 1D Green functions can not explain the source aspects as described above, which suggests that the source inversion using 3D Green functions has a potential to effectively reveal the source process with high accuracy and high resolution.
DE: 7209 Earthquake dynamics and mechanics
DE: 7212 Earthquake ground motions and engineering
SC: Seismology [S]
MN: 2004 AGU Fall Meeting