Fault zone heterogeneities explain depth- dependent pattern and evolution of slow earthquakes in Cascadia

Slow earthquakes including tremor and slow-slip events are recent additions to the conventional
earthquake family and have a close link to megathrust earthquakes. Slow earthquakes
along the Cascadia subduction zone display a diverse behavior at different
spatiotemporal scales and an intriguing increase of events frequency with depth. However,
what causes such variability, especially the depth-dependent behavior is not well understood.
Here we build on a heterogeneous asperities-in-matrix fault model that incorporates differential
pore pressure in a rate-and-state friction framework to investigate the underlying
processes of the observed episodic tremor and slow-slip (ETS) variability. We find that the
variations of effective normal stress (pore pressure) is one important factor in controlling ETS
behavior. Our model reproduces the full complexity of ETS patterns and the depth-frequency
scaling that agree quantitatively well with observations, suggesting that fault zone heterogeneities
can be one viable mechanism to explain a broad spectrum of transient
fault behaviors.