HR: 0800h
AN: S51B-0501    [Abstracts]
TI: Resolution Analysis of Teleseismic Waveform Inversion of Rupture Process of Tsunami Earthquake Using 1D and 2.5D Green's Functions
AU: * Okamoto, T
EM: okamoto.t.ad@m.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551, Japan
AU: Takenaka, H
EM: takenaka@geo.kyushu-u.ac.jp
AF: Department of Earth and Planetary Sciences, Kyushu University, Japan, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
AB: Flat-layered or 1D structure is usually assumed as model structure for source region in the teleseismic waveform analysis of earthquakes, because it is a reasonable approximation for many events in land area. However, for shallow subduction zone earthquakes, the thick ocean (water) layer with dipping ocean bottom and the thick sediments with low seismic wave velocity cause large effects on the teleseismic body waveforms, and these effects are not reproduced by flat-layered structure (e.g., Wiens 1989; Yoshida 1992; Okamoto 1993). In this paper we employ a synthetic resolution test to see the effect of the differences in the Green's functions on the inverted rupture process of a tsunami earthquake: tsunami earthquake occurs very close to the trench axis (e.g., Polet and Kanamori 2000) and the structural effect is the largest of those for the shallow subduction zone earthquakes. We assume a 2.5D realistic near source structure based on a detailed seismic experiments (Kopp et al. 2002) conducted at Java trench where the 2006 Java tsunami earthquake occurred. We compute "realistic" Green's functions for teleseismic body waveforms by a 2.5D FDM (Okamoto 1994; Takenaka and Kennett 1996). "Synthetic data" are then generated by using the 2.5D Green's functions for time-space slip models on a fault with a length of 220 km and a width of 130 km. To the synthetic data we apply a non-linear waveform inversion method in which unit point sources are put at the grid points on the fault and the amplitudes and onset times of them are simultaneously retrieved. We find that if we use the 2.5D or "correct" Green's functions in the inversion, the position of the peaks in the slip models are stably retrieved. On the other hand, considerable misfits are observed between the assumed and inverted slip patterns when we use 1D Green's functions computed for a structure with a water layer and a half space. The peak amplitudes are smaller than the assumed ones and the slips spread over areas larger than the assumed patches of slips (with a size of about 50 km) even when we use 2.5D Green's functions.
DE: 4564 Tsunamis and storm surges
DE: 7203 Body waves
DE: 7209 Earthquake dynamics (1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: 2007 Fall Meeting