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 13 earthquake family and have a close link to megathrust earthquakes. Slow earthquakes along the Cascadia 14 subduction zone display a diverse behavior at different spatiotemporal scales and an intriguing increase of 15 events frequency with depth. However, what causes such variability, especially the depth-dependent 16 behavior is not well understood. Here we build on a heterogeneous asperities-in-matrix fault model that 17 incorporates differential pore pressure in a rate-and-state friction framework to investigate the underlying 18 processes of the observed ETS variability. We find that the variations of effective normal stress (pore 19 pressure) is one important factor in controlling ETS behavior. Our model reproduces the full complexity 20 of ETS patterns and the depth-frequency scaling that agree quantitatively well with observations, 21 suggesting that fault zone heterogeneities can be one viable mechanism to explain a broad spectrum of 22 transient fault behaviors.