DEPENDENCE OF SOURCE TIME FUNCTION ON TECTONIC FIELD

Abstract

Crack models in which nucleation can be treated are physically analysed by considering non-uniform initial stress or strain, and static and sliding frictional stress. The proposed models are, in the strict sence, applicable to physical phenomena near the foci of large earthquakes having bilateral rupture propagation.
Crack models of two kinds are discussed in detail. In one model, rigidity, static and sliding frictional stress are assumed to be constant everywhere. In this case, the proposed model is applied to the 1961 Kitamino and the 1966 Parkfield earthquakes and the initial tectonic fields and frictional stress of these earthquakes are determined.
In the other model, rigidity is assumed to be a function of position. This model yields the result that stress drop is directly proportional to effective stress, defined by the static frictional stress minus the sliding frictional stress, and the final stress is lower than the sliding frictional stress.
In each case, the factors accelerating dislocation motion are a broadly accumulated initial stress and a small ratio of sliding to static frictional stress.
This result is qualitatively the same as in a paper of YAMASHITA (1977). In Case II, it is shown that stress drop is not influenced by the spatial distribution of rigidity but strain drop is heavily influenced by that distribution. Accordingly a treatment like that of Case II is required when the value of strain drop is discussed.