Quasi-static Motions near the San Andreas Fault Zone

Abstract

A technique is presented for computing quasi-static strains and displacements at the surface of a vertically heterogeneous elastic or viscoelastic half-space caused by a dislocation of finite size. The distribution of displacement discontinuity and orientation of the dislocation surface are arbitrary. The technique is applied to the problems of deep stress relaxation on the San Andreas fault. It is found that modern geodetic data do not allow ready distinction between stress relaxation due to deep seismic slip and stress relaxation due to viscoelastic creep. We also investigate tectonic motions in the Imperial Valley and conclude that most of the motion on the southern part of the San Andreas system is occurring in the Imperial Valley. It may also be inferred that deep relaxation of stress has occurred on the Imperial fault since the earthquake there in 1940.