Comparison of episodic and non-episodic non-volcanic tremors in the northern Cascadia subduction zone

Sequences of non-volcanic tremor have been identified along the Nankai and Cascadia subduction zones [41, 151. The source mechanisms of tremor have been attributed to flow-induced rtesonance in fluid-filled conduits [23]. In northern Cascadia, transient surface deformation indicates that slow slip occurs every 13-1 6 months on the inter-plate boundary and landward of the locked zone. Elevated levels of tremor activity have been found to coincide spatially and temporally with slow slip episodes [46]. 1 image two tremor sequences: one which occurs during a slow slip episode (episodic) and another which occurs in between slip episodes (non-episodic). Episodic tremors migrate 150 km along strike from south to north and correlate with the subduction megathrust. Non-episodic tremors do not migrate, and are found mostly at 5-10 km depth within the continental crust. Non-episodic tremors could arise from readjustment of the crust following the preceding slow slip episode.