Fluid pressurization of critically stressed sheared zones can trigger slip mechanisms at work in many geological processes. Using discrete element modeling, we simulate pore-pressure-step creep test experiments on a sheared granular layer under a sub-critical stress state to investigate the micromechanical processes at stake during fluid induced reactivation. The global response is consistent with available experiments. The progressive increase of pore pressure promotes slow steady creep at sub-critical stress states, and fast accelerated dynamic slip once the critical strength is overcome. Our multi-scale analyses show that these two emergent behaviors correlate to characteristic deformation modes: diffuse deformation during creep, and highly localized deformation during rupture. Creep corresponds to bulk deformation while rupture results from grain rotations initiating from overpressure induced unlocking of contacts located within the shear band which, consequently, acts as a roller bearing for the surrounding bulk.

中文翻译：

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流体加压活化的剪切颗粒层的微观力学

临界应力剪切带的流体加压可触发滑移机制在许多地质过程中起作用。我们使用离散元建模模拟了亚临界应力状态下剪切颗粒层上的孔隙压力阶跃蠕变试验实验，以研究流体诱导再活化过程中的微机械过程。全球响应与可用实验一致。孔隙压力的逐渐增加会促进亚临界应力状态下的缓慢稳定蠕变，一旦克服临界强度，就会促进快速加速的动态滑移。我们的多尺度分析表明，这两种突发行为与特征变形模式相关：蠕变期间的扩散变形和破裂期间的高度局部变形。