HR: 16:45h
AN: S54A-04    [Abstracts]
TI: Source Process of the 2007 Niigata-ken Chuetsu-oki Earthquake Derived from Near-fault Strong Motion Data
AU: * Aoi, S
EM: aoi@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenoudai, Tsukuba, 305-0006, Japan
AU: Sekiguchi, H
AF: National Institute of Advanced Industrial Science and Technology, Site 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Morikawa, N
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenoudai, Tsukuba, 305-0006, Japan
AU: Ozawa, T
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenoudai, Tsukuba, 305-0006, Japan
AU: Kunugi, T
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenoudai, Tsukuba, 305-0006, Japan
AU: Shirasaka, M
AF: Japan Meteorological Agency, 1-3-4 Otemachi, Chiyoda-ku, Tokyo, 100-8122, Japan
AB: The 2007 Niigata-ken Chuetsu-oki earthquake occurred on July 16th, 2007, 10:13 JST. We performed a multi- time window linear waveform inversion analysis (Hartzell and Heaton, 1983) to estimate the rupture process from the near fault strong motion data of 14 stations from K-NET, KiK-net, F-net, JMA, and Niigata prefecture. The fault plane for the mainshock has not been clearly determined yet from the aftershock distribution, so that we performed two waveform inversions for north-west dipping fault (Model A) and south-east dipping fault (Model B). Their strike, dip, and rake are set to those of the moment tensor solutions by F-net. Fault plane model of 30 km length by 24 km width is set to cover aftershock distribution within 24 hours after the mainshock. Theoretical Green's functions were calculated by the discrete wavenumber method (Bouchon, 1981) and the R/T matrix method (Kennett, 1983) with the different stratified medium for each station based on the velocity structure including the information form the reflection survey and borehole logging data. Convolution of moving dislocation was introduced to represent the rupture propagation in an each subfault (Sekiguchi et al., 2002). The observed acceleration records were integrated into velocity except of F-net velocity data, and bandpass filtered between 0.1 and 1.0 Hz. We solved least-squared equation to obtain slip amount of each time window on each subfault to minimize squared residual of the waveform fitting between observed and synthetic waveforms. Both models provide moment magnitudes of 6.7. Regarding Model A, we obtained large slip in the south-west deeper part of the rupture starting point, which is close to Kashiwazaki-city. The second or third velocity pulses of observed velocity waveforms seem to be composed of slip from the asperity. Regarding Model B, we obtained large slip in the southwest shallower part of the rupture starting point, which is also close to Kashiwazaki-city. In both models, we found small slip near the rupture starting point, and largest slip at about ten kilometer in the south-west of the rupture starting point with the maximum slip of 2.3 and 2.5 m for Models A and B, respectively. The difference of the residual between observed and synthetic waveforms for both models is not significant, therefore it is difficult to conclude which fault plane is appropriate to explain. The estimated large-slip regions in the inverted source models with the Models A and B are located near the cross point of the two fault plane models, which should have similar radiation pattern. This situation may be one of the reasons why judgment of the fault plane orientation is such difficult. We need careful examinations not only strong motion data but also geodetic data to further explore the fault orientation and the source process of this earthquake.
UR: http://www.k-net.bosai.go.jp/k-net/topics/chuetsuoki20070716/inversion/
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting