HR: 17:00h
AN: S54A-05    [Abstracts]
TI: Source Inversion for the 2007 Chuetsu-oki, Japan, Earthquake: A Case of Difficulty Determining the Source Fault Plane
AU: * Koketsu, K
EM: koketsu@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AU: Miyake, H
EM: hiroe@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AU: Hikima, K
EM: hikima@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113- 0032, Japan
AB: An earthquake with a CMT Mw of 6.6 occurred on July 16, 2007 along the western coast of Niigata prefecture, Japan. This 2007 Chuetsu-oki earthquake is the first large event whose source fault extends to beneath a nuclear power plant. The earthquake is characterized by difficulty determining the source fault plane. The CMT solution by Ekstrom (2007) indicates reverse faulting with conjugate nodal planes dipping to SE and NW. The aftershock distribution (e.g., ERI, 2007; NIED, 2007) shows not only a major trend dipping to SE but also a minor one to NW, so we cannot determine the source fault plane by using this. GSI (2007) found that uniform slips on the both fault planes can reproduce observed static displacements and InSAR image. We first carried out a preliminary source inversion (Kikuchi and Kanamori, 2003) of teleseismic waveforms from IRIS DMC to determine the geometry and depths of the two fault planes. We then performed full source inversions (Yoshida et al., 1996; Koketsu et al., 2004) of strong motion records observed by K-NET and KiK-net of NIED, and seismometers of TEPCO in the nuclear power plant, for the two fault planes, respectively. Both the full source inversions resulted in almost the same average residual, so that we were still unable to determine the source fault plane. We next constructed the characterized source models consisting of three asperities from the inverted slip distributions and synthesized broadband seismograms, using the empirical Greenfs function method (Irikura, 1986). However, we again found almost the same fit to observed seismograms in the both cases. Two or three distinct pulses can be seen in the seismograms observed at stations close to the source region including those at the nuclear power plant. Since they correspond to three asperities in the characterized source model, we picked the differences of arrival times of the initial motion and the first and third pulses. We then determined the relative location of the first asperity to the hypocenter and that of the third asperity to the first one. The first asperity was finally located in neighborhood of the hypocenter at the same depth, and the third asperity is in the western part of the source region at a depth shallower than that of the hypocenter. These implies that some slips may occur on the fault plane dipping to SE and the other close to the hypocenter might be located on the crossing of the conjugate fault planes.
DE: 7203 Body waves
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting