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Specification of a Soon-to-Occur Seismic Faulting in the Tokai District, Central Japan, Based Upon Seismotectonics

2011; American Geophysical Union; Linguagem: Inglês

10.1029/me004p0297

2329-0307

Katsuhiko ISHIBASHI,

earthquake and tectonic studies

The 'Tokai earthquake' expected in the Tokai district, the Philippine Sea coast of central Japan, is the most important target now in the Japanese earthquake prediction program. Its long-term and short-term prediction efforts are among the most advanced cases in the world. It is also a big social problem in Japan because of its preestimated catastrophic disaster. This paper reviews in detail the long-term prediction research of this earthquake and presents the most probable fault model. The expected event is considered an interplate earthquake due to the underthrusting of the Philippine Sea plate beneath southwest Japan at the Nankai-Suruga trough. Based on the analyses of source mechanisms of the 1854 Ansei Tokai (M=8.4) and the 1944 Tonankai (M=8.0) earthquakes, the most probable rupture zone of the coming earthquake is the 'Suruga trough thrust' in Suruga Bay and its southwestern extension. The first-order approximation fault model is as follows: dip direction, N72°W; dip angle, 34°; length, 115 km; width, 70 km; reverse dip slip, 3.8 m; left-lateral strike-slip, 1.3 m; seismic moment, 1.6×1028 dyne·cm; stress drop, 50 bar; magnitude, 8.3. Crustal movements in the Suruga Bay region during the last 80 years or so are well interpreted as the preparatory strain accumulation for this faulting. Geomorphological features and historical seismic activities in this region are generally in good harmony with this prediction. The seismic gap for 126 years on the Suruga trough thrust since 1854 and the considerable amount of strain accumulation in this region estimated from geodetic survey data suggest a fairly high probability of a near-future occurrence of this faulting. And, if the event is a little smaller-scale, it may occur earlier. The seismogenic tectonism in the Suruga Bay region is rather complicated due to the collision of the Izu Peninsula with the Japanese Islands, and the subduction of the Philippine Sea plate at the Suruga trough has not been established yet by geophysical evidences. For further refinement of the long-term prediction of the Tokai earthquake, it is necessary to obtain more clear view on the real dynamical and physical process of plate convergence in the Izu collision zone as a total system.