HR: 1340h
AN: S43A-1044    [Abstracts]
TI: Kinematic Source Rupture Model and Near-source Ground Motion Simulations of the 2005 West Off Fukuoka Prefecture, Japan, Earthquake
AU: * Asano, K
EM: k-asano@egmdpri01.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Iwata, T
EM: iwata@egmdpri01.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: A large crustal earthquake occurred at the offshore of Fukuoka City, southwest Japan, on March 20, 2005. It was the first damaging shallow crustal earthquake in Japan which hit large cities since the 1995 Hyogo-ken Nanbu (Kobe) earthquake. The strong ground motions were densely observed by the nation-wide strong motion seismograph networks. At first, the kinematic source rupture process was estimated by the waveform inversion of strong motion waveforms. The methodology of waveform inversion follows Sekiguchi et al.(2000). The S-wave parts of the observed ground velocities in 0.05-1 Hz are analyzed. A fault plane model is assumed based on the moment tensor solution and the aftershock distributions. The fault plane is divided into subfaults, and the source-time function at each subfault is expressed by a series of smoothed ramp functions. Green's functions are calculated by the discrete wavenumber method (Bouchon, 1981) with the reflection and transmission matrix (Kennett and Kerry, 1979) assuming a one-dimensional layered structure model. The rupture started with relatively small slip-velocity. The large slip area or asperity was observed at approximately 5 km southeast of the hypocenter, which ruptured approximately 3.5 s after the rupture initiation at the hypocenter. The slip-direction was almost pure left-lateral strike slip, which was consistent with the regional stress field. The total seismic moment was estimated to be 1.15×10¹⁹ Nm (M_W 6.6). Then, we conducted a three-dimensional ground motion simulation up to 1 Hz using the finite difference method (Pitarka, 1999). A three-dimensional underground structure model is assumed based on the gravity basement contour map (Komazawa, 2005). Here, we assumed that the gravity basement corresponds to the seismic bedrock (V_S 2.85 km/s). Following the velocity structure model by Nakamichi and Kawase (2002), we also assumed three sedimentary layers above the bedrock, and the shear-wave velocity of the top layer is 0.6 km/s, which corresponds to Paleogene sand stone layer. The Quaternary layers are not thick except the center of Fukuoka City. The large ground motions were expected around the source region and inside the basin structure in Fukuoka. The overall features of waveform fittings in Fukuoka City were fairly good. However, the NS components of ground velocities were underestimated at several stations in the center of Fukuoka City, where the relatively thick Quaternary deposits exist. The amplification effect of the superficial layer in this area on the ground motions could be necessary considered for more realistic evaluation.
DE: 7209 Earthquake dynamics (1242)
DE: 7212 Earthquake ground motions and engineering seismology
SC: Seismology [S]
MN: Fall Meeting 2005