Bi-Material Effects on Critical Jump Distance Over Step-Overs

Abstract

Step-overs can impede rupture propagation, but if breached, they may generate a large destructive earthquake. By performing dynamic rupture simulations on step-overs in both homogeneous and bi-material media, we demonstrate that the bi-material effect significantly influences the critical jump distance, the maximum jump step width that a rupture can jump across. In the positive direction, which is defined as the direction of motion of the softer material, the critical jump distance is greatly enlarged, especially on the compliant side, because of the existence of a tensile normal stress pulse and large slip pulse. In the homogeneous case the rupture can jump only a 1 km releasing step and is stopped by a 1 km restraining step. In contrast, with a 20% material contrast in wave velocity, the critical jump distance increases to 11 km for restraining steps, and 2 km for releasing steps. In the negative direction, supershear rupture is easier to generate because of stress perturbation beyond the rupture front. Besides the Burridge-Andrews supershear, direct-transition supershear can also be noticed in the negative direction under certain condition. However, the critical jump distance in the negative direction is still suppressed because of the dominant bi-material effect over the supershear effect. Our study may shed light on the earthquake hazard assessment due to step-overs in bi-material media.