From Distributed Damage to Strain Localization in Rocks during Brittle Creep

The transition from distributed damage to strain localization in rocks during brittle creep remains mechanistically unclear. Through uniaxial creep experiments on polystyrene plates with a preexisting closed crack, we demonstrate that low-stress creep is governed by frictional slip with shear stress redistribution rather than fracture, mediated by rate- and state-dependent friction (RSF). A finite element model of rock with randomly distributed microcracks, integrating RSF behavior with damage mechanics, reproduces the spatio-temporal evolution of microcracking during brittle creep. The simulated acoustic emission analysis reveals that the initial distributed damage, characterized by independent events, transitions gradually to strain localization through a prolonged fault nucleation progress, marked by progressive clustering and event triggering. We identify four stress modulation modes of microcracks that govern the competition between stress concentration and relaxation, elucidating the micromechanical evolution in brittle creep. By bridging microscale time-dependent friction to macroscale rupture, this framework offers a physics-based interpretation of failure precursors, with implications for earthquake hazard mitigation and brittle material failure prediction.