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Insight into complex rupturing of the immature bending normal fault in the outer slope of the Japan Trench from aftershocks of the 2005 Sanriku earthquake (Mw = 7.0) located by ocean bottom seismometry
Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Japan Agency for Marine-Earth Science and Technology, 3173-25, Showa-cho, Kanazawa-ku, Yokohama 236-0001, Japan
Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Seismological and Volcanological Department, Japan Meteorological Agency, 1-3-4, Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan
Seismological and Volcanological Department, Japan Meteorological Agency, 1-3-4, Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan
Technical Department, Sendai District Meteorological Observatory, 1-3-15 Gorin, Miyagino-ku, Sendai 983-0842, Japan
Technical Department, Sendai District Meteorological Observatory, 1-3-15 Gorin, Miyagino-ku, Sendai 983-0842, Japan
The distribution of aftershocks of a large (M w = 7.0) normal faulting earthquake beneath the outer slope of the Japan Trench in 2005, measured in 2007 using ocean bottom seismographs, indicates that the earthquake was involved with a set of conjugate normal faults. Although the faults reach to the upper mantle, the estimated Vp and Vp/Vs show no remarkable changes that can be related to extensive hydration in the crust or uppermost mantle. The absence of horst-graben topographic structure in the rupture area suggests that immaturity of the bending fault system is responsible for the relatively unhydrated lithosphere. Several earthquakes below the aftershock zone may belong to the lower plane seismicity of the shallow double seismic zone. Because no earthquakes were recorded in the area for more than 80 years before the 2005 event, shallow extensional and deep compressive earthquakes may be activated concurrently in the focal area of this earthquake.
Received 30 January 2009; accepted 24 June 2009; published 30 July 2009.
Citation: (2009), Insight into complex rupturing of the immature bending normal fault in the outer slope of the Japan Trench from aftershocks of the 2005 Sanriku earthquake (Mw = 7.0) located by ocean bottom seismometry, Geochem. Geophys. Geosyst., 10, Q07O18, doi:10.1029/2009GC002415.
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