Dynamic rupture on a bimaterial interface governed by slip-weakening friction

Abstract

We perform 2-D finite-difference calculations of mode II rupture along a bimaterial interface governed by slip-weakening friction, with the goal of clarifying rupture properties and the conditions leading to the development of unilateral wrinkle-like pulses. The simulations begin with an imposed bilateral rupture in a limited source region. Rupture properties outside the imposed source are examined for ranges of values of the degree of material contrast γ across the fault, the difference between static fs and dynamic fd coefficients of friction, and the difference between static friction and initial shear stress. The results show that mode II rupture evolves with propagation distance along a bimaterial interface, for broad ranges of realistic conditions, to a unilateral wrinkle-like pulse in the direction of slip on the compliant side of the fault. These conditions span in our calculations the ranges fs−fd < 0.4 and γ > 2–5 per cent. When the difference between the static friction and initial shear stress is smaller, the evolution to unilateral wrinkle-like pulses occurs for smaller values of γ. The amount of slip increases with propagation distance, due to the incorporation of slip-weakening friction, in contrast to earlier results based on Coulomb and Prakash–Clifton friction laws with slip-independent coefficient. In all cases leading to wrinkle-like pulses, the rupture velocity in the preferred (+) propagation direction is V+r≈CGR, where CGR is the generalized Rayleigh wave speed. Simulations with imposed rupture speed in the source region close to the slower P wave speed P− can excite, in addition to the primary wrinkle-like pulse in the preferred direction with V+r≈CGR, a weak pulse in the opposite (−) direction with V−r≈P−. In some cases leading to bilateral crack-like propagation (e.g. fs−fd= 0.7), the rupture velocities in the opposite directions are V+r≈P+ (the faster P wave speed) and V−r≈P−, with the initial supershear crack front in the + direction followed by a pulse with V+r≈CGR.