On stress accumulation and fault slip in the lithosphere

Abstract

A mechanism of accumulation of shear stress in the neighborhood of a locked vertical strike-slip fault in the lithosphere is considered. The fault is taken to be situated in an elastic layer resting on and in welded contact with, a visco-elastic half space, in which shear stresses are maintained far away from the fault by tectonic forces. Exact solutions are obtained for the displacements and stresses in the system in the absence of fault slip, taking into account the displacements and stresses present initia1ly. It is shown that stress accumulation would occur continuously in the upper layer near the fault ti1l the fault slips suddenly, generating an earthquake. Exact solutions are next obtained for the displacements and stresses fo1lowing the fault slip, taking into account the displacements and stresses present before fault slip, and it is shown that stress accumulation would again occur in the upper layer, ti1l the fault slips again. The mathematical results are applied to some relevant observations on the accumulation of shear strain in the neighborhood of the San Adreas fault. It is shown that comparison of the mathematical results obtained and the observations on the ground deformations on the surface near the fault can be used to arrive at reasonable estimates for the times between consecutive slips on the active strike slip faults. The results are also expected to lead to greater insight into the problem of earthquake prediction. It is shown that, if sufficient data on surface deformation are available, the results can be used to estimate the effective viscosity of the lower lithosphere.