HR: 0800h
AN: S51B-0512    [Abstracts]
TI: Source Rupture Process of the 2007 Noto Hanto Earthquake, Japan, Obtained from Strong Ground Motion and GPS Data
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: The 2007 Noto Hanto earthquake (M_JMA 6.9) occurred near the west coast of the Noto peninsula, central Japan, on March 25, 2007. This is an inland crustal earthquake having oblique slip source mechanism. The strong ground motions from this event brought severe damages on wooden houses in and around near-source region (e.g., Wajima city and Anamizu town). Near-source strong motion records have great potential to investigate detailed source rupture process in space and time. However, strong ground motions are generally affected by amplifications due to the subsurface structure under the station. It is quite important for obtaining a reliable source model to use appropriate velocity structure models. We have employed an approach in which each strong motion station has its identical velocity structure model. Here, one-dimensional velocity structure model for each strong motion station is constructed after an optimization procedure using the aftershock's waveform data. Firstly, a reference velocity structure model is assumed by referring to the refraction survey using controlled sources by Aoki et al. (1972) and microtremor array measurements by Kanno et al. (2003). This reference velocity structure model consists of three sedimentary layers on the seismic bedrock. Then, the thickness of each sedimentary layer for each station is estimated to fit the observed waveforms of the aftershock by using the Genetic Algorithm. Twelve strong motion stations of K-NET (Kinoshita, 1997) and KiK-net (Aoi et al., 2000) are employed in this study. We succeeded to get a reasonable velocity structure model for each station to give a good fit of the main S-wave part in the observation. The kinematic source rupture process of the 2007 Noto Hanto earthquake is estimated by the linear waveform inversion using multiple time windows (Hartzell and Heaton, 1983). The spatiotemporal smoothing constraints to stabilize the solution are introduced following Sekiguchi et al. (2000). The velocity waveform data in 0.05-1 Hz at 12 strong motion stations are used. The static GPS-measured displacement data at 18 GEONET stations (Miyazaki et al., 1997) are also included in the data set. Static displacement at each station is calculated from the daily coordinate solutions released from GEONET. By including GPS data, we can get a broadband source model in this analysis. The obtained source model shows that large slip is observed in shallow portion of the fault plane near the hypocenter and the spatial slip distribution seems rather simple. This model reproduces both of the strong motion and GPS data fairly well. But, we might need to adjust the geometry of the fault plane to get better fitting of the GPS-measured displacement data. The difference between the source model from strong motion and GPS data and that from strong motion only is not significant. We could get a robust source model using only strong motion data with well-calibrated Green's functions for strong motion data. Finally, in order to evaluate effectiveness of our approach, we will compare the result obtained by the station- dependent velocity structure models with the one obtained from a uniform velocity structure model.
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting