The Initiation of Frictional Motion—The Nucleation Dynamics of Frictional Ruptures

Frictional interfaces lose stability via earthquake-like ruptures, which are close analogues of shear cracks that well-described by fracture mechanics. Interface however, need to be first formed—or nucleated. Rupture nucleation therefore determines the onset friction, replacing concept a characteristic “static friction coefficient”. Utilizing rupture arrest at an imposed barrier, we experimentally determine locations, times and stresses origin each subsequent event. This enables us study process real-time measurements real contact area local strain. Nucleation events initiate as 2D patches expand nearly constant velocities, vnuc, orders magnitude lower than dynamic velocities described conventional We find that: (a) has location-dependent stress thresholds, (b) vnuc is roughly proportional level, (c) continues until patch size reaches Ltran ∼ LG, Griffith length for (d) scaling time τ = Ltran/vnuc, exhibit self-similar dynamics (e) ruptures' cohesive zones not fully established significantly beyond Ltran. Many details governed topography, invariant under successive in mature interfaces. Topography-dependent include: precise site location, geometry, critical thresholds proportionality with stress. believe these results shed considerable light on both how frictional motion triggered earthquake initiation.