Automated detection and location of tectonic tremor along the entire Cascadia margin from 2005 to 2011

Abstract

We have constructed an automated routine to identify prominent bursts of tectonic tremor and locate their source region during time periods of raised amplitude in the tremor passband. This approach characterizes 62 episodes of tectonic tremor between 2005 and 2011, with tremor epicenters forming a narrow band spanning the entire length of the Cascadia Subduction Zone. We find a range of along-strike lengths in individual episodes, but the length appears proportional to both duration and geodetic moment, consistent with proposed scaling laws for slow earthquake phenomena. Examination of individual episodes in detail reveals intriguing updip–downdip migration patterns, including slow updip migration during initiation and repetitive downdip migration between different episodes. The broader catalog of tremor episodes refines the inferences from earlier work that episodic tremor and slip are segmented along-strike and correlated with apparent seismogenic zone segmentation in most cases. The overall band of tremor is offset ∼50 km from the downdip edge of interseismic coupling along the central and northern parts of the subduction zone. Along the southern part of the subduction zone, it is adjacent to this boundary, suggesting that the locked and transition zones may be more closely linked in southern Cascadia.