Abstract Brittle rock failure spans an exceptionally broad spectrum of strain rates, from slow creep to dynamic rupture, yet a unified physical model capturing this rate‐dependent strength evolution remains elusive. Here we present a micromechanics‐based model that integrates rate‐and‐state friction (RSF) on microcracks with inertial effect at crack tips to predict rock strength across this full spectrum. Uniaxial creep experiments on single closed cracks with varying orientations reveal decelerating slip at subcritical stresses, well described by RSF laws. Such time‐dependent creeping slips can initiate wing cracks under sustained loading, motivating an extension of the classical wing crack model to incorporate RSF‐controlled slip at low strain rates and inertial effect at high strain rates. The resulting micromechanical model identifies three rate‐dependent strength regimes in rocks with pervasive microcracks: (a) a healing regime at low rates, where strength increases with decreasing rate due to frictional healing; (b) a frictional strengthening regime at intermediate rates, governed by rate‐sensitive slip on microcracks; and (c) an inertia‐dominated regime at high rates, where dynamic fracture resistance increases sharply. The model unifies classical Hoek‐Brown and Mohr‐Coulomb criteria within this micromechanical framework. It can be extended to incorporate environmental factors, including temperature, pore‐pressure, and subcritical crack growth, which collectively govern the rate dependence of rock strength. These results offer new insights into rate‐ and stress‐dependent crustal strength, helping to explain intraplate versus interplate earthquake recurrence patterns and pervasive rupture in the upper crust. It also improves the physical understanding and prediction of brittle rock failure across diverse geological settings.
Jiang et al. (Wed,) studied this question.