Fault slip behavior during episodic tremor and slow slip (ETS) events, which occur at the deep extension of subduction zone megathrust faults, is believed to be related to cyclic fluid processes that necessitate fluctuations in pore-fluid pressures. In most subduction zones, a layer of anomalously low seismic wave velocities [low-velocity layer (LVL)] is observed in the vicinity of ETS and suggests high pore-fluid pressures that weaken the megathrust. Using repeated seismic scattering observations in the Cascadia subduction zone, we observe a change in the seismic velocity associated with the LVL after ETS events, which we interpret as a response to fluctuations in pore-fluid pressure. These results provide direct evidence of megathrust fault-valve processes during ETS.

中文翻译：

---

地震性震颤和滑动过程中大推力断层阀行为的地震证据。

人们认为，在俯冲带巨推断层的深部扩展发生的偶发性震颤和慢滑（ETS）事件中的断层滑动行为与循环流体过程有关，该循环流体过程需要孔隙流体压力的波动。在大多数俯冲带中，在ETS附近发现了异常低的地震波速度层[低速层（LVL）]，这表明高孔隙流体压力削弱了巨推力。使用卡斯卡迪亚俯冲带中的重复地震散射观测，我们观察到ETS事件发生后与LVL相关的地震速度的变化，我们将其解释为对孔隙流体压力波动的响应。这些结果提供了在ETS期间大推力断层阀过程的直接证据。