Benjamin Idini, Jean Paul Ampuero 

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.