Dynamics of fault interaction: parallel strike‐slip faults

We use a two‐dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures. Our results indicate that a strike‐slip earthquake is unlikely to jump a fault step wider than 5 km, in correlation with field observations of moderate to great‐sized earthquakes. We also find that dynamically propagating ruptures can jump both compressional and dilational fault steps, although wider dilational fault steps can be jumped. Dilational steps tend to delay the rupture for a longer time than compressional steps do. This delay leads to a slower apparent rupture velocity in the vicinity of dilational steps. These “dry” cases assumed hydrostatic or greater pore‐pressures but did not include the effects of changing pore pressures. In an additional study, we simulated the dynamic effects of a fault rupture on ‘undrained’ pore fluids to test Sibson's (1985, 1986) suggestion that “wet” dilational steps are a barrier to rupture propagation. Our numerical results validate Sibson's hypothesis by demonstrating that the effect of the rupture on the ‘undrained’ pore fluids is to inhibit the rupture from jumping dilational stepovers. The basis of our result differs from Sibson's hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments.