SCEC2024 Poster #136: Back-propagating Earthquakes on a Simple Fault

Group B, Poster #136, Fault and Rupture Mechanics (FARM)

Back-propagating Earthquakes on a Simple Fault

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Poster Presentation

2024 SCEC Annual Meeting, Poster #136, SCEC Contribution #13843 VIEW PDF

Back-propagating earthquakes, characterized by their reversal through previously ruptured regions, have been observed across diverse geological settings with the advancement of seismic measurements. Previous studies have proposed that fault heterogeneity may facilitate back propagation. However, the underlying physics of back-propagating earthquakes remains poorly elucidated. Here, we employ earthquake simulations with rate-state friction to reveal that back-propagating fronts can occur on a frictionally homogeneous fault if ruptures are forced to propagate unilaterally, for example when a fault is loaded from the edges. We use analytical models to demonstrate that lateral propagation, coupl...ed with velocity-dependent friction, precludes crack-like solutions at constant residual stress. Back propagation then occurs when a pulse-like rupture transitions into a crack-like rupture, a phenomenon that can occur under less stringent conditions than previously assumed and does not require fault heterogeneity. The shift between rupture modes is driven by velocity-weakening friction and happens when the slip rate becomes non-uniform and decreases below a specific threshold. Our research presents a simple, fundamental model for back-propagating earthquakes, indicating their potential to be more prevalent than previously acknowledged.
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