Cascadia Slow Earthquake Behaviors Modulated by Tectonic and Environmental Forcings

Abstract Slow earthquakes, including episodic tremor and slip (ETS), are highly sensitive to small stress perturbations, yet their links to tectonic and non‐tectonic forcings remain unclear. Previous studies suggest that annual hydrological cycle dominates the tremor seasonal behavior in northern Cascadia. But over a longer time range, the tremor seasonal pattern seems significantly changed. Here, we systematically examine major stress perturbations toward influencing tremor and slow slip event (SSE) activities in Cascadia and identify two distinct patterns: an incongruent tremor seasonal variation that cannot be explained by hydrological forcing and a long‐term change in the locations where ETS events nucleate and their propagation directions. The tremor seasonality is better explained by stress variation due to SSEs, while the long‐term ETS evolution likely reflects spatiotemporal stress redistribution on subduction fault interface through stress feedback of past major ETS events and potential stress balancing along fault strike.