A model of foreshock occurrence

Abstract

We have constructed a model for the occurrence of foreshocks and foreshock sequences. The foreshocks as well as the main shock are assumed to occur because of the abrupt coalescence of pre-existing cracks. Coalescence occurs if the stress intensity factors at the crack tips exceed a certain critical value. In the sub-critical state each crack undergoes accelerated extension quasi-statically due to stress corrosion, until it reaches the critical state, at which point growth becomes catastrophic.