Slip distributions on faults: effects of stress gradients, inelastic deformation, heterogeneous host-rock stiffness, and fault interaction

Abstract

Fault slip distributions are commonly assumed to be symmetrical about a central slip maximum, however, slip distributions in nature are often asymmetric. Although slip along an idealized fault is expected to follow an elliptical distribution after a single slip event in an elastic material, the slip distribution may be modified if the fault propagates or if additional slip events occur. Analytically and numerically computed fault-slip distributions in an elastic medium indicate that: (1) changes in the (frictional) strength along a fault; (2) spatial gradients in the stress field; (3) inelastic deformation near fault terminations; and (4) variations of the elastic modulus of the host rock can cause strong deviations from idealized symmetrical distributions along single-slip event faults. A relatively stiff body adjacent to or cut by a fault will tend to reduce fault slip in its vicinity and tends to flatten the slip profile where it is cut by the fault. Sharp slip gradients develop near the interface between relatively soft and stiff materials. The interaction of faults within about one fault radius of one another can strongly influence slip gradients. Inelastic processes, caused by stress perturbations in the stepover region of echelon faults, may link individual segments and thereby create a slip distribution resembling that of a single fault.