Stress and deformation along wavy frictional faults

Abstract

Locally inhomogeneous stress states are expected along faults owing to slip on geometrically irregular fault surfaces. We use an analytical model of elastic deformation along a wavy frictional fault to evaluate the variation in local stress state as a function of surface roughness, elastic modulus, slip, coefficient of friction, and far‐field stress. The total stress state along the fault may be described by the sum of a basic stress component resulting from frictional slip on a planar fault surface and a perturbed stress component resulting from the presence of roughness. Roughness produces a variation in normal stress across the fault surface, and assuming roughness and modulus appropriate to crustal faults, the normal stress should be reduced to a near‐zero magnitude locally, such that separation of fault walls is likely. The large variation in normal stress along the fault surface resulting from fault roughness may be responsible, in part, for complexity in moment release during large earthquakes and for lateral variation in seismic coupling along faults. The variation in principal stress orientations and magnitudes along a fault increases with a decrease in the coefficient of friction of the fault. The location and size of regions with a high likelihood for brittle failure depend on the orientation of the far‐field principal stress and fault friction. The average orientation of the principal stresses in the region of likely failure is not the same as the far‐field principal stress orientation. Although inversion of earthquake and fabric data for stress orientation along a fault may be possible, the model results suggest that inversion results are insufficient to determine far‐field stress states and fault friction without additional independent data.