Poster Presentation

Rupture propagation across step-overs wider than a few kilometers has never been observed during historical earthquakes. We map step-overs from a new compilation of 31 surface ruptures from strike-slip earthquakes and regional fault maps and measure their width. We classify each step-over as breached or unbreached depending on whether the rupture renucleated on the fault segment across the step-over, and as restraining or releasing depending on the kinematics of fault slip. We did not observe step-overs larger than 1.4 km wide breached without the assistance of hard-linking structures. Using a simple model based on linear elastic fracture mechanics, we use the mapped widths and rupture lengths on the source fault leading to each step-over to estimate the Coulomb stress change experienced on the receiver fault across the step-over. We find that ruptures seldom renucleate on receiver faults with stress changes below a critical threshold of 20% of the source-fault stress drop. This stress level far exceeds the stress change required to trigger aftershocks or nucleate secondary fractures in the volume surrounding rupturing faults.