Fault‐Zone Damage Promotes Pulse‐Like Rupture and Back‐Propagating Fronts via Quasi‐Static Effects

Abstract

Damage zones are ubiquitous components of faults that may affect earthquake rupture. Simulations show that pulse‐like rupture can be induced by the dynamic effect of waves reflected by sharp fault zone boundaries. Here we show that pulses can appear in a highly damaged fault zone even in the absence of reflected waves. We use quasi‐static scaling arguments and quasi‐dynamic earthquake cycle simulations to show that a crack turns into a pulse after the rupture has grown larger than the fault zone thickness. Accompanying the pulses, we find complex rupture patterns involving back‐propagating fronts that emerge from the primary rupture front. Our model provides a mechanism for back‐propagating fronts recently observed during large earthquakes. Moreover, we find that slow‐slip simulations in a highly compliant fault zone also produce back‐propagating fronts, suggesting a new mechanism for the rapid tremor reversals observed in Cascadia and Japan.