HR: 1340h
AN: S43A-1043    [Abstracts]
TI: Source Process and Near-source Strong Ground Motion Generation of the 2004 Mid Niigata Prefecture (Chuetsu), Japan, Earthquake
AU: * Iwata, T
EM: iwata@egmdpri01.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Asano, K
EM: k-asano@egmdpri01.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Yamanaka, H
EM: yamanaka@depe.titech.ac.jp
AF: Interdisciplinary Graduate School of Science and Technology, Tokyo Inst., Tech., Nagatsuda, Midori-ku, Yokohama, 226-8503 Japan
AU: Yamada, N
EM: yamada.n@ckcnet.co.jp
AF: Chuo Kaihatsu Corporation, Nishi-Aoki 3-4-2, Kawaguchi, 332-0035 Japan
AU: Fukumoto, S
EM: fukumoto@tokyosoil.co.jp
AF: Tokyo Soil Research, Higashigaoka 2-11-16, Meguro-ku, Tokyo, 152-0021 Japan
AB: The 2004 Mid Niigata Prefecture Earthquake occurred on October 23, 2004 in the central Japan with large strong ground motions in the near source region. We estimate a source rupture process of this event using strong motion records. Then we simulate strong ground motions in the source area using the obtained source model together with the three-dimensional underground structure model derived by Yamanaka et al. (2005). To obtain a source model we performed the kinematic linear waveform inversion using multiple time-windows by Sekiguchi et al. (2000). We assumed the hypocenter and the fault plane by event relocation research studies (Kato et al., 2005; Okada et al., 2005; Shibutani et al., 2005). We used the S-wave portion of velocity waveforms that were bandpass-filterd between 0.05 <ETH> 1 Hz, and we used 16 strong motion stations of K-NET, KiK-net, JMA and Niigata Prefecture Government near source area. We constructed a one-dimensional underground structure model for GreenOs function calculation at each site by forward waveform modeling of aftershock records. We used the S-wave velocity structure model proposed by Yamanaka et al. (2005a) as a reference model, and modified the thickness of the layer using GA approach. Green's functions were calculated by the discrete wavenumber method (Bouchon, 1981) with the reflection and transmission matrix (Kennett and Kerry, 1979). The final slip distribution obtained by the inversion shows that the rupture propagated to shallower part from the rupture starting point. The large slip occurred shallower part of the assumed fault plane. Slip distribution is more or less complex. Total seismic moment is 1.06_~10**19Nm (Mw6.6), with maximum slip is 1.4m. The synthetic waveforms fit the observed ones fairly well. The first time-window front propagates at a velocity of 2.4km/s, which is a little bit smaller value among ordinary crustal earthquakes. Yamanaka et al. (2005a) conducted microtremor array observation to estimate S-wave velocity structure in the source area. Yamanaka et al.(2005b) constructed a three-dimensional underground structure model (from engineering bedrock to seismic bedrock) in this area using their microtremor observation result, gravity anomaly information, and boring information. The underground structure is very complex, e.g. the seismic bedrock depth is changing from approximately 6km to 0km (outcrop rock area) in this source region. We conduct ground motion simulation using the obtained source model and this three-dimensional underground structure model. We obtained strong ground motions in the hanging wall area with deep basin, that corresponds to severely damaged area. Because of the limitation of the underground structure model, it is hard to discuss the validity of the ground motion distribution quantitatively. However, characteristics of the simulated ground motions at several stations in the strong motion area match more or less those of the observed records.
UR: http://sms.dpri.kyoto-u.ac.jp/
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: Fall Meeting 2005