HR: 17:40h
AN: S34C-07    [Abstracts]
TI: Effects of heterogeneous structures of the seismic velocity and the stress field on earthquake generations elucidated by dense temporary seismic networks
AU: * Kato, A
EM: akato@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Sakai, S
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Kurashimo, E
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Igarashi, T
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Iidaka, T
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Hirata, N
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Iwasaki, T
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Kanazawa, T
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: observation of 2007 Noto Earthquake, G
AU: observation of 2007 Niigata Earthquake, G
AB: Within recent 3 years, three large thrust-type inland earthquakes (the 2004 Mid-Niigata Prefecture Chuetsu Earthquake, the 2007 Noto Hanto Earthquake, and the 2007 Niigata Prefecture Chuetsu Offshore Earthquake) have occurred at the southern end of the eastern margin of the Japan Sea. The margin was initially formed as a rifted passive margin, mainly during the early Miocene when the Japan Sea opened. In the margin, E-W shortening has continued since the late Pliocene. Thus, it is considered that the complex structures, associated with both the crustal stretching and the folding, can potentially nucleate the mainshock and trigger a sequence of aftershocks for three large earthquakes. Therefore, it is important to image the complex seismogenic structures and stress field around the source region and clarify their relations to the rupture process, or stress concentration process. We have immediately deployed dense temporary seismic networks in the source region, after the occurrence of each mainshock. On the basis of accurate aftershock distributions, aftershocks associated with each mainshock rupture are aligned along high-dipping fault planes. Tomographic analysis clearly shows that each mainshock rupture occurred along a velocity boundary between the hanging wall and the footwall. It is therefore interpreted that each mainshock fault plane might be a reactivated reverse fault through inversion tectonics. Furthermore, it is found from stress tensor analysis that the maximum compressional stress axis tends to rotate near the mainshock hypocenter. Present results suggest that heterogeneous structures of crust and the stress field are of crucial importance to earthquake generation. In future, we will investigate heterogeneous structures in Kanto- region using new data set obtained by MeSO-net (Metropolitan Seismic Observation network in Japan), to evaluate seismic potentials.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
DE: 8045 Role of fluids
DE: 8164 Stresses: crust and lithosphere
SC: Seismology [S]
MN: 2007 Fall Meeting