On‐Fault Geological Fingerprint of Earthquake Rupture Direction

Abstract

AbstractHow earthquake ruptures evolve and propagate are major outstanding questions in seismology. Our current understanding is limited to modern events captured by seismic networks, making it impossible to observe rupture propagation that occurred during earthquakes in the distant past. Here we propose a new method to discern the rupture propagation directions of past large earthquakes based on geological features preserved on fault slip planes. These features—called slickenlines—are striations formed during seismic slip and record dynamic fault movement during past surface‐breaking earthquakes. We develop a theoretical framework that links slickenline curvature with rupture mode and rupture propagation direction for all faulting types and test our model using a global catalogue of historical surface‐rupturing earthquakes with seismologically constrained rupture directions. Our results reveal that historical observations are consistent with theoretical predictions, thus providing a robust way to uncover the rupture directions of large earthquakes that lack instrumental data.