Study of non-volcanic tremors in the Cascadia subduction zone

I locate for the first time several episodic and minor tremor sequences along the Cascadia subduction zone from Vancouver Island to northern California between February 2003 and December 2005 using a single location method. My results suggest that Cascadia tremors occur within a distributed deformation zone surrounding the plate interface. I observe spatial and temporal correlations between the greatest magnitude of slow slip and the location of the first day of tremor activity for some episodic sequences in northern Cascadia. In addition to episodic events, minor tremors have also occurred in the region of slow slip, but during different time intervals. In northern California and Oregon, tremors are mainly located where the interplate thermal structure is 550°C–600°C, while the distribution of northern Cascadia tremor epicentres borders the downdip extension of the thermal transition zone in northern Puget Sound, and places the majority of tremors where the interplate thermal structure is 500°C–550°C. In Cascadia, microearthquakes are located much closer to tremor epicenters in comparison with the large earthquakes. A big percentage of tremors in northern and southern Cascadia occur when the b-value is close to an extremum, and this is more obvious for crustal earthquakes. The only clearly identified gap in tremor activity in northern Cascadia correlates with the lowest measured coda Q in the region.