Fault reactivations induced by deep excavation can pose significant challenges to underground construction or resource extraction. Laboratory experiments on rock faults demonstrate that unloading-induced fault reactivations obey the Coulomb failure criterion derived from loading-induced events. However, the effect of stress path during unloading on the failure criterion and rupture dynamics of fault reactivations remains poorly understood. Here, we present findings from a series of laboratory experiments aimed at elucidating the effect of the unloading path on the failure criterion and rupture dynamics of fault reactivations. We conducted experiments under various stress conditions, examining two cases of unloading paths. In Case I, we unloaded the minimum principal stress, while in Case II, the maximum principal stress was unloaded. Strain gauges and high-speed photography were employed to capture the transient dynamic rupture process. Our investigations have yielded new insights into the effect of unloading path on the rupture dynamics when the fault is reactivated. In Case I, we observed fault reactivations resembling those loading-induced events characterized by forward sliding. Conversely, in Case II, fault reactivations associated with stress reversal produce mild reversed sliding with lower stress drop and rupture velocity. Furthermore, we find that there is a remarkable reduction in static friction for reversed sliding, indicating that the failure criterion for fault reactivation is influenced by the stress path. We demonstrate that enhanced stress heterogeneity, caused by stress reversal, serves as a mechanism for reduced static friction. These findings contribute to our understanding of the mechanisms underlying fault reactivations, particularly those involving reversed sliding.

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关于卸载引起的故障再激活：应力路径对失效准则和断裂动力学的影响

深部挖掘引起的断层重新激活可能会给地下施工或资源开采带来重大挑战。岩石断层的实验室实验表明，卸载引起的断层重新激活遵循由加载引起的事件导出的库仑破坏准则。然而，卸载过程中的应力路径对断层重新活动的失效准则和破裂动力学的影响仍然知之甚少。在这里，我们提出了一系列实验室实验的结果，旨在阐明卸载路径对故障准则和断层重新激活的破裂动力学的影响。我们在各种应力​​条件下进行了实验，检查了两种卸载路径的情况。在情况一中，我们卸载了最小主应力，而在情况二中，卸载了最大主应力。采用应变仪和高速摄影来捕捉瞬态动态破裂过程。我们的研究对断层重新激活时卸载路径对破裂动力学的影响产生了新的见解。在案例一中，我们观察到断层重新激活，类似于那些以向前滑动为特征的负载诱发事件。相反，在情况 II 中，与应力反转相关的断层重新激活会产生轻微的反转滑动，并具有较低的应力降和破裂速度。此外，我们发现反向滑动的静摩擦力显着降低，这表明断层重新活动的失效准则受到应力路径的影响。我们证明，由应力反转引起的应力异质性增强是减少静摩擦的机制。这些发现有助于我们理解断层重新激活的机制，特别是那些涉及反向滑动的机制。