A MECHANISM TO EXPLAIN THE EARTHQUAKES AROUND JAPAN BY THE PROCESS OF PARTIAL MELTING

Partial melting at the hypocentral depths (30 to 40km) is closely related to great earthquakes occurring in comparatively high heat flow zones such as the sea just south off the southwestern Japan. It is obvious from the thermal gradient curves in such high heat flow zones that temperature at the hypocentral depths approaches the melting point of wet peridotite. Under such circumstances the partial melting proceeds by the effect of some pressure decrease or temperature increase associated with the huge tectonic force acting on the rocks. The partial melting will yield some increase in volume. Consequently some stresses will be originated and added to the tectonic forces due to the mantle convection and other origins to trigger earthquakes. Changes in seismic wave velocities owing to the partial melting is calculated in this paper using the Lindemann's equation based upon the Debye's theory of specific heat.