Résumé
Earthquake nucleation and propagation can be explained using two basic concepts, crustal strength and fault rheology. Despite numerous experimental and modeling studies, the way in which a faulted crust generates a seismic cycle under loading is still controversial. We discuss earthquake generation using a 2-D Finite Element Model which includes relevant features of geodynamical problems such as rheological layering, dynamic Coulomb faulting and relative plate velocity. The occurrence of a deep nucleation is explained by the strong viscosity drop at the base of the seismogenic layer, without any transition of frictional properties of the fault. Rather, viscosity contrast causes a stress transfer around the fault that reloads the fault plane during the postseismic phase. We argue that this mechanism may explain the seismic cycle for large faults in the continental crust. Copyright 1998 by the American Geophysical Union.