HR: 0800h
AN: G51B-0823    [Abstracts]
TI: Space-time Evolution of Interplate Slip beneath Hokkaido, Japan before and after the 2003 Tokachi-oki Earthquake (M8.0) Inferred from GPS
AU: * Yui, S
EM: yui@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aramaki 6-3, Aobaku, Sendai, 980-8578 Japan
AU: Miura, S
EM: miura@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aramaki 6-3, Aobaku, Sendai, 980-8578 Japan
AU: Hasegawa, A
EM: hasegawa@aob.geophys.tohoku.ac.jp
AF: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aramaki 6-3, Aobaku, Sendai, 980-8578 Japan
AU: Yagi, Y
EM: yagi-y@arsia.geo.tsukuba.ac.jp
AF: Graduate School of Life and Environmental Sciences,University of Tsukuba, Tennodai 1-1-1, Tsukuba, 305-8572 Japan
AB: A giant interplate thrust earthquake with M8.0 occurred off Tokachi , Hokkaido, Northern Japan on September 26, 2003 (hereafter referred to as TE). GPS measurements revealed significant co- and post-seismic crustal deformations. This type of earthquake releases stress built up due to interplate coupling, and thus it is important to evaluate the variation of both interplate coupling and postseiemic slip in space and time to understand earthquake cycles in the subduction system. There occurred another interplate thrust event with M7.1 off Kushiro on November 29, 2004 (hereafter referred to as KE), about 100 km northeast of the coseimic rupture area of TE. This drives us to the question whether the co- and post-seismic slip of TE might affect the occurrence of KE. We utilized a geodetic inversion technique devised by Yagi and Kikuchi (GRL, 2003) to reproduce spatio-temporal distribution of interplate coupling before TE and the postseismic slip after TE. The estimated strong coupling areas before TE are consistent with major asperities beneath Hokkaido. and have not changed in time. This indicates that the stress has accumulated on the TE asperity with almost constant rate. The area of the dominant postseismic slip grew at the northeast of the coseismic rupture area, extending toward the next event, KE. The after-slip distribution is complementary to the coseismic rupture estimated by waveform inversion. This characteristic has already been pointed out for some other interplate events by Yagi and Kikuchi (GRL, 2003) and Yagi et al. (GRL, 2003). The quasi-static slip distribution estimated by using repeating earthquakes (Uchida et al., presented in this meeting) coincides with the after-slip area of 60 cm or more estimated by this study. Comparing the time evolution of slip obtained by the two different methods, the slip amount estimated by GPS exceeds that by repeating earthquakes in general. In the best case, however, the quasi-static slip by repeating earthquakes amounts to about 70 to 80 % of geodetic estimation at areas demonstrating the major postseismic slip.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1209 Tectonic deformation (6924)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Geodesy [G]
MN: Fall Meeting 2005