HR: 17:25h
AN: S34C-06    [Abstracts]
TI: Local stress concentration on the seismic belt along the Japan Sea coast inferred from numerous precise focal mechanisms -Implications for the brittle-ductile interaction model-
AU: * Iio, Y
EM: iio@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
AU: Kawanishi, R
EM: iio@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
AU: YUkutake, Y
EM: yukutake@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, Tennoudai 3-1, Tsukuba, 305-0006, Japan
AU: Shibutani, T
EM: shibutan@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
AU: Katao, H
EM: katao@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
AB: We found a rotation of the maximum horizontal compressional stress axis near the seismic belt along the Japan Sea coast in the Chugoku district, Southwest Japan. The azimuth of the axis near the seismic belt is WNW, while that in the surrounding area is EW. The maximum horizontal compressional stresses of the EW direction are widely observed in the shallow crust in the inland plate along the Nankai trough. That of the WNW direction is unusual in the Chugoku, Kinki and Shikoku districts in Japan, so it suggests the local stress concentration probably due to ductile faulting in the lower crust beneath the seismic belt. The data used are obtained by two dense seismic observations. The first was conducted by the group for the dense aftershock observations of the 2000 Western Tottori earthquake. They installed 72 seismic stations for 40 days with 4-5 km spans in the aftershock area and recorded more than 3000 aftershocks. The second was conducted by the group of the joint seismic observation in the Seinan area, Japan. They installed 40 online seismic stations for about two years and recorded more than 1000 earthquakes occurring in the Chugoku district, Southwest Japan. We estimated the stress field from inversions of numerous polarity data using the Horiuchifs method. In the aftershock area of the 2000 Tottori earthquake, we conducted the stress inversions at a bin with a 3 km width, and succeeded to estimate spatial changes in the stress field along the fault strike, which is perpendicular the strike of the seismic belt. Consequently, we found the detailed stress change across the seismic belt. The result is explained by ductile faulting in the lower crust predicted by the brittle-ductile interaction model.
DE: 1209 Tectonic deformation (6924)
DE: 7215 Earthquake source observations (1240)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: 2007 Fall Meeting