A New Framework Describing the Nucleation of Frictional Ruptures and Earthquakes: Experiments and Theory

The mechanism of rupture nucleation, the process by which ruptures are formed, is still not well-understood in the friction, fracture, and earthquake mechanics fields. Rupture propagation is relatively well-understood, as it can be described by the framework of fracture mechanics. Rupture nucleation, which is inherently unpredictable, remains elusive. Nucleation is observed to be a slow process relative to the propagation of the rupture that follows it. Numerous unique features that characterize the nucleation process elude existing models. Here, we first review recent experimental studies that have revealed intriguing characteristic properties of frictional rupture nucleation. We then describe a recently derived theoretical formulation that extends fracture mechanics (utilizing energy balance) to provide a full quantitative description of both extremely slow (aseismic) nucleation dynamics and their consequent transition to rapid (seismic) rupture. This approach highlights the importance of geometry—both interface confinement and the 2D shape of the rupture patch itself—in the rupture process. This framework provides a seamless transition between these seemingly disparate regimes, providing a new and fundamental understanding of both frictional and earthquake nucleation. These ideas may also be relevant for understanding material creep, which generally precedes catastrophic failure. ▪ Nucleation, the slow initial process of rupture formation, is qualitatively different than the rapid propagation of ruptures once formed. ▪ The transition from slow expansion to rapid propagation of frictional ruptures is related to the finite width of a frictional interface. ▪ A new model extends fracture mechanics to provide a mechanical description of slow rupture expansion during nucleation. ▪ This framework provides understanding of earthquake nucleation along natural faults and creep processes preceding catastrophic failure.