Elevated pore fluid pressure is proposed to contribute to slow earthquakes along shallow subduction plate boundaries. However, the processes that create high fluid pressure, disequilibrium compaction and dehydration reactions, lead to different effective stress paths in fault rocks. These paths are predicted by granular mechanics frameworks to lead to different strengths and deformation modes, yet granular mechanics do not predict their effects on fault stability. To evaluate the role of fluid overpressure on shallow megathrust strength and slip behavior, we conducted triaxial shear experiments on chlorite and celadonite rich gouge layers. Experiments were conducted at constant temperature (130 and 100°C), confining pressure (130 and 140 MPa), and pore fluid pressures (between 10 and 120 MPa). Fluid overpressure due to disequilibrium compaction was simulated by increasing confining and pore fluid pressure synchronously without exceeding the target effective pressure, whereas overpressure due to dehydration reactions was simulated by first loading the sample to a target isotropic effective pressure and then increasing pore fluid pressure to reduce the effective pressure. We find that the effects of fluid pressure and stress path on the mechanical behavior of the chlorite and celadonite gouges can generally be described using the critical state soil mechanics (CSSM) framework. However, path effects are more pronounced and persist to greater displacements in chlorite because its microstructure is more influenced by stress path. Due to its effects on microstructure, the stress path also imparts greater control on the rate-dependence of chlorite strength, which is not predicted by CSSM.

中文翻译：

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流体超压期间浅俯冲剪切带的路径和滑移相关行为

提出升高的孔隙流体压力有助于沿浅俯冲板块边界发生慢地震。然而，产生高流体压力、不平衡压实和脱水反应的过程导致断层岩石中不同的有效应力路径。颗粒力学框架预测这些路径会导致不同的强度和变形模式，但颗粒力学并不能预测它们对断层稳定性的影响。为了评估流体超压对浅层巨型逆冲强度和滑移行为的作用，我们对富含绿泥石和青瓷石的泥岩层进行了三轴剪切实验。实验在恒温（130 和 100°C）、围压（130 和 140 MPa）和孔隙流体压力（10 和 120 MPa 之间）下进行。不平衡压实引起的流体超压是通过同步增加围压和孔隙流体压力而不超过目标有效压力来模拟的，而脱水反应引起的超压是通过首先将样品加载到目标各向同性有效压力，然后增加孔隙流体压力以降低压力来模拟。有效压力。我们发现，流体压力和应力路径对绿泥石和青瓷泥凿岩力学行为的影响通常可以使用临界状态土力学（CSSM）框架来描述。然而，路径效应更加明显，并持续到绿泥石中更大的位移，因为其微观结构更容易受到应力路径的影响。由于其对微观结构的影响，应力路径还可以更好地控制绿泥石强度的速率依赖性，这是 CSSM 无法预测的。