Possibility of a major earthquake in the tokai district, Japan and its pre-estimated seismotectonic effects

Abstract

Crustal deformations, tsunamis and seismic intensity are pre-estimated for a large hypothetical earthquake, which it is feared may occur in the Tokai district along the Nankai trough. The long-term seismic quiescence since 1854, as well as the high rate of the present crustal movements in the district, form the principal evidence for the risk of the approaching catastrophe. The location and the mode of faulting in this earthquake are hypothesized in reference to the source mechanisms of the recent and historical earthquakes there. The fault parameters thus assumed are as follows: dip direction: N30°W; dip angle: 25°; fault dimension : 100 km × 70 km; dislocation: 4 m (reverse dip-slip: 3.8 m; right-lateral strike-slip: 1.3 m). The following are the principal conclusions: (a) the eastern part of the epicentral region including the Point Omaezaki will rise up about 100 cm, whereas the western part covering Ise and Mikawa bays will subside about 10–30 cm; (b) the coast extending from Omaezaki to the Shima peninsula will receive tsunami waves as high as 3 m in maximum, which may be locally amplified by the factor 2 or more on the rias coast along the Shima peninsula; (c) the Tokai coastal region with thick alluvium layers may suffer seismic damages as severe as those experienced in the 1854 Ansei I earthquake.