HR: 14:35h
AN: S53A-05    [Abstracts]
TI: Aftershock Distribution of the 2004 Niigata-Chuetsu Earthquake (Mj = 6.8) and Heterogeneous Structure in and Around the Source Region
AU: * Shibutani, T
EM: shibutan@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Iio, Y
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Matsumoto, S
AF: Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, Shin'yama, Shimabara, Nagasaki, 855-0843 Japan
AU: Katao, H
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Matsushima, T
AF: Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, Shin'yama, Shimabara, Nagasaki, 855-0843 Japan
AU: Ohmi, S
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Takeuchi, F
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Uehira, K
AF: Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, Shin'yama, Shimabara, Nagasaki, 855-0843 Japan
AU: Nishigami, K
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Enescu, B
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Hirose, I
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Kano, Y
AF: Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Kohno, Y
AF: Graduate School of Sciences, Kyushu University, Hakozaki, Higashi-ku, Fukioka, 812-8581 Japan
AU: Korenaga, M
AF: Graduate School of Sciences, Kyushu University, Hakozaki, Higashi-ku, Fukioka, 812-8581 Japan
AU: Mamada, Y
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Miyazawa, M
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Tatsumi, K
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Ueno, T
AF: Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto, 606-8502 Japan
AU: Wada, H
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, 611-0011 Japan
AU: Yukutake, Y
AF: Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto, 606-8502 Japan
AB: The 2004 Niigata-Chuetsu Earthquake (Mj = 6.8) occurred on 23 October 2004 in the northeastern part of the Niigata-Kobe Tectonic Zone where large strain rates (> 0.1 ppm/y contraction) were found from GPS data analyses (Sagiya et al., 2000). The strong ground motion caused by the mainshock (1,722 gal was observed near the epicenter) severely destroyed ~5,000 houses and killed 40 people. We deployed three temporary online seismic stations in the aftershock area, combined data from the temporary stations and from permanent stations located around the aftershock area, and determined aftershock locations with a joint hypocenter determination (JHD) technique. The resulting aftershock distribution showed that major events including the mainshock, the maximum aftershock (Mj = 6.5), etc. formed at least three different fault planes parallel or perpendicular to each other. We also found that large differences in the travel time residuals (~1 s for P and ~2 s for S) between Niigata Plain to the west and Echigo Mountains to the east from the source area significantly affected the aftershock locations. We carried out a tomographic inversion of the P- and S- travel times for 3-D Vp and Vs structures. The station corrections obtained in the JHD process were subtracted from the travel times beforehand. The result showed that the source area was highly heterogeneous. Low velocity anomalies to the west and high velocity anomalies to the east were clearly found down to ~10 km deep. One of the boundaries of the anomalies sloped downward to the west and corresponded well to the mainshock fault. These features are probably a main cause that many larger aftershocks occurred in the sequence of the 2004 Niigata-Chuetsu Earthquake.
DE: 7209 Earthquake dynamics and mechanics
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2005 Joint Assembly