Relation between effective friction and fault slip rate across the Northern San Andreas fault system

The San Andreas Fault system is a complex tectonic ensemble that accommodates most of the relative plate motion between the Pacific and the North American plates. The structure and theological properties of the faults vary along the plate boundary and lead to the distribution of deformation that we observe today. In order to learn more about the mechanical behaviour of such a fault system, a model of the northern California fault system is built, constrained by heat flow data, GPS and palaeoseismological measurements of slip rates (on the San Andreas, the Maacama and Bartlett Springfaults), and stress orientations. Our basic assumption is that the upper crust has a high frictional strength and that major faults represent weak zones with a lower effective friction. Several combinations of effective fault frictions on the three major faults of the system in the model are tested. We find that slight variations of the effective friction angle on one of the three active strands lead to an important redistribution of slip rates through the system. If present in nature, this fault behaviour could explain why fault slip rates vary in time, as suggested by slip rate variations over geological scales in intracontinental fault Systems.