Seismic activity and deformation process of the overriding plate in the northeastern Japan subduction zone

We estimated the temperature distribution within the crust of the northeastern Japan are from P wave velocity perturbations obtained by travel time tomography. By comparing the estimated temperature distribution with the focal depth distribution of shallow, precisely relocated microearthquakes, we found that the brittle to ductile or stick-slip to stable-sliding transition occurs at the similar to 400 degrees C isotherm and that the transition depth has considerable lateral variations. The brittle seismogenic zone, the upper portion of the crust, becomes locally thin in the P wave low-velocity areas, where the temperature is estimated to be relatively high. Concentration of shallow microearthquakes, high topography and relatively large contractile deformation of the crust are also observed in these low-velocity areas. Active faults are not distributed in the low-velocity areas but lie just along the edge of those areas or outside them. All these observations suggest that earthquake occurrence and deformation within the crust is governed, to a considerable degree, by the thermal regime of this volcanic are, which is characterized by a horizontally inhomogeneous distribution of temperature. (C) 2000 Elsevier Science B.V. All rights reserved.