Rate-and-State Model Casts New Insight into Episodic Tremor and Slow-slip Variability in Cascadia

Advances in geodetic and seismic observations have led to the discovery of Episodic Tremor and Slow-slip (ETS). ETS in Cascadia subduction zone occurs semiregularly and shows intriguing spatio-temporal variability reportedly associated with frictional properties and stress conditions. Yet the origin of complex ETS behaviors remains largely unknown. Here we develop a laboratory-based rate-and-state asperity-in-matrix subduction fault model, supported by geological observations of exhumed fault with heterogeneous frictional properties and pore pressure variation, to reproduce all ETS variability in good agreement with observations. Our results show that differential pore pressure plays a crucial role in affecting fault behaviors. Regions of asperities with decreased pore pressure tend to have increased tremor. Our study suggests that ETS variability can be used to probe otherwise enigmatic fault zone properties.