Stable fault sliding and earthquake nucleation

The process of earthquake nucleation is studied assuming that faults are rupture surfaces on which sliding is controlled by friction. Empirical slip laws indicate that, under constant ambient conditions, friction depends on time, slip rate and slip history. Regular stick-slip behaviour is induced by velocity weakening, a negative dependence of friction on slip rate. The instability occurs when the rate at which friction decreases becomes greater than the rate at which the applied stress must increase to produce an advance of fault slip. The possibility that this condition is fulfilled depends on the velocity dependence and on the spatial distribution of friction on the fault. A critical nucleation width of the dislocation is associated with the instability and is controlled by the friction distribution, which determines the size of the initial slipping patch.