Interplate coupling and relative plate motion in the Tokai district, central Japan, deduced from geodetic data inversion using ABIC

Abstract

The spatial distribution of the strength of interplate coupling between the subducting Philippine Sea and overlying continental plates in the Tokai district, central Japan, was investigated in detail through the inversion analysis of geodetic data using Akaike's Bayesian Information Criterion (ABIC). The geodetic data used for the analysis are annual rates of level changes (1972‐1984) and horizontal length changes (1977‐1988), which presumably represent average crustal movements during the interseismic period. The result of the inversion analysis shows the existence of a strongly coupled region extending from 10 to 30 km in depth. The total seismic moment accumulated in this area since the last event (the 1854 Ansei earthquake) is roughly estimated to be 5.5 × 1027 dyne cm, which corresponds to Ms= 7.8. The interplate coupling becomes weaker toward the shallower and deeper portions. This is consistent in general tendency with a rheological model inferred from petrological viewpoints. The strength of coupling also tends to decrease toward northeast over the west coast of Suruga Bay. The direction of plate convergence inferred from the inversion analysis is oriented N30°W. This is significantly different from the direction of relative plate motion between the Philippine Sea and Eurasian plates but concordant with that between the Philippine Sea and North American plates. Copyright © 1993, Wiley Blackwell. All rights reserved