HR: 1340h
AN: T53A-1111    [Abstracts]
TI: Focal mechanism distribution of main- and after- shock of the 2005 off Miyagi Earthquake (M7.2) by using radiation pattern of P- and S- wave
AU: * Suzuki, K
EM: suzuki@aob.geophys.tohoku.ac.jp
AF: RCPEV, Graduate School of Science, Tohoku Univ., JAPAN, Aramaki-Aza-Aoba 6-6, Aoba- ku, Sendai, 980-8578, Japan
AU: Hino, R
EM: hino@aob.geophys.tohoku.ac.jp
AF: RCPEV, Graduate School of Science, Tohoku Univ., JAPAN, Aramaki-Aza-Aoba 6-6, Aoba- ku, Sendai, 980-8578, Japan
AU: Yamamoto, Y
EM: yyama@aob.geophys.tohoku.ac.jp
AF: RCPEV, Graduate School of Science, Tohoku Univ., JAPAN, Aramaki-Aza-Aoba 6-6, Aoba- ku, Sendai, 980-8578, Japan
AU: Ito, Y
EM: yito@aob.geophys.tohoku.ac.jp
AF: RCPEV, Graduate School of Science, Tohoku Univ., JAPAN, Aramaki-Aza-Aoba 6-6, Aoba- ku, Sendai, 980-8578, Japan
AU: Kanazawa, T
EM: kanazawa@eri.u-tokyo.ac.jp
AF: ERI, Tokyo Univ., JAPAN, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Yamada, T
EM: yamada@eri.u-tokyo.ac.jp
AF: ERI, Tokyo Univ., JAPAN, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Shinohara, M
EM: mshino@eri.u-tokyo.ac.jp,
AF: ERI, Tokyo Univ., JAPAN, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Uehira, K
EM: uehira@sevo.kyushu-u.ac.jp
AF: SEVO, Kyushu Univ., JAPAN, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan
AU: Tanaka, M
EM: tan-tanaka@met.kishou.go.jp
AF: Japan Meteorological Agency, Ohte-machi 1-3-4, Chiyoda-ku, Tokyo, 100-8122, Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, Natsushima-cho 2-15, Yokosuka, 237-0061, Japan
AB: Interplate earthquakes of magnitude of 7.5 have occurred along the subduction plate boundary of the Miyagi-Oki region, middle part of the Japan Trench area, repeatedly on about 40 years intervals. In 2005, interplate earthquake with magnitude of 7.2 occurred in this area, considered to be the rupture of one of the asperities of the 1978 earthquake (M7.4) (Okada et al., 2005: Yaginuma et al., 2007). Hino et al. (2007) and Suzuki et al. (2007) determined the focal mechanism distribution of main- and after- shock of the 2005 earthquake by using ocnean bottom seismometers (OBSs) and coastal stations. They classified the aftershocks into two types according to their focal mechanism solutions: 1) mainshock type having focal mechanism similar to the mainshock and 2) non-mainshock type with focal mechanism dissimilar to the mainshock. Based on this classification, Suzuki et al. (2007) discovered that the non-mainshock type events tend to occur near the edge of the areas with large co- and post- seismic moment release. However, they used only the polarities of the first P wave arrivals for determining focal mechanisms. Therefore the estimation errors are large for earthquakes which are not located very beneath the seismic network due to poor station coverage, and some of the aftershocks could be classified into another groups due to the large estimation errors. In this paper, we improve the accuracies of focal mechanisms by using P- and S- wave radiation pattern to discuss whether the systematic variation of the mechanism of the aftershocks are substantial. Our new result, in which we use the radiation pattern to calculate the focal mechanisms, suggests that focal mechanism patterns show more distinguished relationship with the co- and post-seismic slip area of the mainshock than previous studies: Non-mainshock-type events are distributed near the edge of the large co- and post-seismic slip areas; mainshock-type events occur within post-seismic slip area. We consider that the non- mainshock type events occurred reflecting the stress change due to the fault motion, both the mainshock and the afterslip. The high seismicity of the non-mainshock type events on the peripheries of the areas of the co- and post- seismic slips may reflect the existence of barriers prohibiting rupture propagation and giving rise to stress concentration.
DE: 7220 Oceanic crust
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8123 Dynamics: seismotectonics
DE: 8168 Stresses: general
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting