Earth Planets Space, Vol. 58 (No. 12), pp. 1543-1548, 2006LETTER
Ryota Hino1, Yojiro Yamamoto1, Asako Kuwano1, Minoru Nishino1, Toshihiko Kanazawa2, Tomoaki Yamada2, Kazuo Nakahigashi2, Kimihiro Mochizuki2, Masanao Shinohara2, Kouetsu Minato3, Gen Aoki3, Nariaki Okawara4, Masayuki Tanaka4, Masao Abe4, Eiichiro Araki5, Shuichi Kodaira5, Gou Fujie5, and Yoshiyuki Kaneda5
1Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
2Earthquake Research Institute, The University of Tokyo, Tokyo 113-0032, Japan
3Sendai District Meteorological Observatory, Japan Meteorological Agency, Sendai 983-0842, Japan
4Seismological and Volcanological Department, Japan Meteorological Agency, Tokyo 100-8122, Japan
5Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan
(Received November 30, 2005; Revised February 1, 2006; Accepted April 29, 2006; Online published February 2, 2007)
The preliminary hypocenter distribution of the 2005 Off Miyagi Prefecture earthquake and its aftershocks is estimated using data from five ocean bottom and six onshore seismic stations located around the rupture area of the earthquake. The epicenter of the mainshock is relocated at 38.17°N, 142.18°E, and the focal depth is estimated to be 37.5 km. The aftershocks surrounding the mainshock hypocenter form several clusters that are concentrated along a distinct landward dipping plane corresponding to the plate boundary imaged by the previous seismic experiment. The strike and dip angles of the plane agree well with those of the focal mechanism solution of the mainshock. The size of the plane is about 20×25 km2 in the strike and dip directions, which is similar to that of the large coseismic slip area. The up-dip end of the planar distribution of the aftershocks corresponds to the bending point of the subducting oceanic plate, suggesting that the geometry of the plate boundary affects the spatial extent of the asperity of the 2005 earthquake.
Key words: Off Miyagi Prefecture earthquake, interplate seismicity, Ocean bottom seismographs.