A detailed field and experimental investigation of the mechanisms responsible for fault zone weakness will be conducted by collaborators with expertise in the natural and experimental deformation of rocks. The study will concentrate on fault gauge from the San Andreas, Punchbowl and San Gabriel faults as these faults are thought to have slipped under small resolved shear stresses. The results of this study will provide an independent estimate of the mechanisms responsible for slip localization along faults of the San Andreas system, and will be of considerable importance to studies of major shallow-level fault zones worldwide.
