Earth Planets Space, Vol. 58 (No. 12), pp. 1549-1554, 2006LETTER
Tadashi Yaginuma1, Tomomi Okada1, Yuji Yagi2, Toru Matsuzawa1, Norihito Umino1, and Akira Hasegawa1
1Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
2Graduate School of Life and Environmental Sciences,University of Tsukuba, Tsukuba 305-8572, Japan
(Received December 15, 2005; Revised March 8, 2006; Accepted September 1, 2006; Online published February 2, 2007)
A large earthquake (M7.2) occurred along the plate boundary offMiyagi Prefecture (Miyagi-Oki), northeastern Japan, on August 16, 2005. In this area, large earthquakes (~M7.5) have occurred repeatedly at intervals of about 37 years, and more than 27 years have passed since the last event occurred. To estimate the relationship between this earthquake and the previous events, we determined coseismic slip distribution by this 2005 Miyagi- Oki earthquake by adopting the seismic waveform inversion method of Yagi et al. (2004) and compared it with that of the previous 1978 Miyagi-Oki earthquake. We performed two cases of the inversions; inversion using only far-field seismograms and that using far-field seismograms and local seismograms simultaneously. Both results show that a large slip occurred near the hypocenter and rupture extended to the westward deeper portion. Considering that the rupture area of the 2005 event partly overlapped with the southeastern part of that of the 1978 event, suggests this result the possibility that plural asperities exist which cause the sequence of Miyagi-Oki earthquakes and that the 2005 event ruptured one of such asperities, although the previous 1978 event ruptured all the asperities at one time.
Key words: Asperity, subduction zone, interplate earthquake, slip distribution.