Earthquakes as Dynamic Fracture Phenomena

Abstract

AbstractA large earthquake unlocks a fault‐zone via dynamic rupture while releasing part of the elastic energy stored during the interseismic stage. As earthquakes occur at depth, the analyses of earthquake physics rely primarily on experimental observations and conceptual models. A common view is that the earthquake instability is necessarily related to the frictional weakening that is commonly observed in shear experiments under seismic slip velocities. However, recent experiments with frictional interfaces in brittle acrylics (e.g., Svetlizky & Fineberg, 2014, https://doi.org/10.1038/nature13202) and rocks (e.g., Passelegue et al., 2020, https://doi.org/10.1038/s41467-020-18937-0) have explicitly demonstrated that no characteristic frictional strength exists. Namely, prior to nucleation, frictional interfaces can sustain a wide range of applied stresses (“overstresses”) that exceed the residual stresses, which are the stresses along the interface that remain after the sliding. Moreover, the experimentally observed singular stress‐fields and rupture dynamics are precisely those predicted by fracture mechanics (Freund, 1998). We therefore argue here that earthquake dynamics are best understood in terms of dynamic fracture mechanics and not governed by the frictional properties of faults. In this view, rupture dynamics are driven by the release of the elastic energy due to overstresses, whereas the values of the residual stresses and the energy dissipation are determined by fault frictional properties.