Geophysical and geological studies provide evidence for cyclic changes in fault-zone pore fluid pressure that synchronize with or at least modulate slip events. A hypothesized explanation is fault valving arising from temporal changes in fault zone permeability. In our study, we investigate how the coupled dynamics of rate and state friction, along-fault fluid flow, and permeability evolution can produce slow slip events. Permeability decreases with time, and increases with slip. Linear stability analysis shows that steady slip with constant fluid flow along the fault zone is unstable to perturbations, even for velocity-strengthening friction with no state evolution, if the background flow is sufficiently high. We refer to this instability as the “fault valve instability.” The propagation speed of the fluid pressure and slip pulse, which scales with permeability enhancement, can be much higher than expected from linear pressure diffusion. Two-dimensional simulations with spatially uniform properties show that the fault valve instability develops into slow slip events, in the form of aseismic slip pulses that propagate in the direction of fluid flow. We also perform earthquake sequence simulations on a megathrust fault, taking into account depth-dependent frictional and hydrological properties. The simulations produce quasi-periodic slow slip events from the fault valve instability below the seismogenic zone, in both velocity-weakening and velocity-strengthening regions, for a wide range of effective normal stresses. A separation of slow slip events from the seismogenic zone, which is observed in some subduction zones, is reproduced when assuming a fluid sink around the mantle wedge corner.

中文翻译：

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故障阀不稳定性：慢滑事件的机制


地球物理和地质研究为断层带孔隙流体压力的周期性变化提供了证据，这些变化与滑移事件同步或至少调节滑移事件。一个假设的解释是由断层带渗透率的时间变化引起的断层瓣。在我们的研究中，我们研究了速率和状态摩擦、沿断层流体流动和磁导率演变的耦合动力学如何产生慢滑事件。渗透性随时间降低，随滑移而增加。线性稳定性分析表明，如果背景流动足够高，则沿断层带的恒定流体流动的稳态滑移对扰动不稳定，即使对于没有状态演变的速度增强摩擦也是如此。我们将这种不稳定性称为“故障阀不稳定性”。流体压力和滑移脉冲的传播速度（随磁导率增强而变化）可能远高于线性压力扩散的预期速度。具有空间均匀特性的二维模拟表明，断层阀不稳定性发展为慢滑事件，以沿流体流动方向传播的地震滑移脉冲的形式出现。我们还对巨型逆冲断层进行了地震序列模拟，同时考虑了与深度相关的摩擦和水文特性。模拟从地震带下方的断层阀不稳定性中产生准周期性慢滑事件，在速度减弱和速度加强区域，对于广泛的有效法向应力。在一些俯冲带中观察到的慢滑事件与成地震带的分离，当假设地幔楔角周围有流体下沉时，可以重现。