A rate-and-state model for episodic tremor and slow-slip events with megathrust earthquake cycles in Cascadia

Abstract:

Episodic tremor and slow-slip (ETS) events in Cascadia subduction zone are located downdip of seismogenic zone and show rich spatiotemporal patterns with an intriguing increase of frequency with depth. Meanwhile, large earthquakes have been notably absent in Cascadia since the last 1700 M9 megathrust earthquake. Understanding the mechanism of ETS and its possible interaction with seismogenic zone is crucial for earthquake hazard estimation. Here we make initial efforts to develop a rate-and-state friction based megathrust earthquake and ETS cycle model, constrained by geodetic and seismic observations. The model consists of a seismogenic region reproducing megathrust earthquakes approximately every 400 years, and an asperity-in-matrix seismic-aseismic transition region generating ETS events of various magnitudes and intervals comparable to the observations in northern Cascadia. Our asperity-in-matrix mechanics model is able to reproduce the full hierarchy of ETS patterns observed in Cascadia, suggesting that fault zone heterogeneity can be one viable mechanism to explain a broad spectrum of transient fault behaviors. Our preliminary model results show ETS displays variations throughout an earthquake cycle. Our current focus is to understand how ETS behavior changes pre-, co- and post-megathrust earthquake.