[S-CG44] Science of slow-to-fast earthquakes

[SCG44-10] The Fundamental Physics of the Onset of Frictional Motion: How does friction start?

*Jay Fineberg¹, Shahar Gvirtzman¹ (1.The Hebrew University of Jerusalem)

Keywords:friction, fracture, earthquake nucleation, earthquake dynamics

Recent experiments have demonstrated that rapid rupture fronts, akin to earthquakes, mediate the transition to frictional motion. Moreover, once these dynamic rupture fronts (“laboratory earthquakes”) are created, their singular form, dynamics and arrest are well-described by fracture mechanics. Ruptures, however, need to be created within initially rough frictional interfaces, before they are able to propagate. This is the reason that “static friction coefficients” are not well-defined; frictional ruptures can nucleate for a wide range of applied forces. A critical open question is, therefore, how the nucleation of rupture fronts actually takes place. We experimentally demonstrate that rupture front nucleation is prefaced by slow nucleation fronts. These nucleation fronts, which are self-similar, are not described by our current understanding of fracture mechanics. The nucleation fronts emerge from initially rough frictional interfaces at well-defined stress thresholds, evolve at characteristic velocity and time scales governed by stress levels, and propagate within a frictional interface to form the initial rupture from which fracture mechanics take over. These results are of fundamental importance to questions ranging from earthquake nucleation and prediction to processes governing material failure.

Figure: Nucleation is mediated by slowly propagating nucleation fronts. a, A sequence of nucleation fronts preceding a dynamic earthquake-like rupture. A(x,z,t) is the normalized change in contact area within a small section of a frictional interface. Its slow 2D evolution is described by Xi(t), which denotes the leading edge of a nucleation front in x. b, Propagation of Xi(t) where the coloured dots correspond to the snapshots in a. Dashed line: The nucleation-front velocity is orders of magnitude less than the rupture velocity (∼500-1000 m/s) of the earthquake that is triggered by this front.

Reference: Gvirtzman, S and Fineberg, J. , “Nucleation fronts ignite the interface rupture that initiates frictional motion”, Nature Physics 17, 1037-1042 (2021).