Abstract
The focal process of deep-focus earthquakes is modelled physically using a viscous frictional law. Numerical experiments are conducted in which the equation of crack propagation derived by YAMASHITA (1976) and the heat conduction equation are solved simultaneously. In this way, the interaction between fault motion and thermal conduction is taken into consideration. When the frictional characteristics of a deep-focus earthquake are described by a transient creep equation, the sliding frictional stress initially increases rapidly as the dislocation continues. However, when the temperature on the dislocation surface becomes significantly higher than the initial temperature or exceeds the solidus temperature, the sliding frictional stress begins to decrease. Efficient fault motion depends on this decrease in sliding frictional stress, and also requires a large effective stress in order to overcome the resistance caused by the initial increase of sliding frictional stress. Effective stress is defined as the static frictional stress minus the sliding frictional stress. This paper shows that a large stress drop is caused by a large effective stress and therefore the fact that deep-focus earthquakes have large stress drops is fully explained by the model proposed in this paper.
