Segmentation in Episodic Tremor and Slip All Along Cascadia

Mike R Brudzinski
Miami University

Richard M. Allen
University of California Berkeley

AGU Fall Meeting 2006
Eos Trans. AGU, 87(52), Fall Meet. Suppl., Abstract T53G-05

Recent developments in the scientific study of the Cascadia subduction zone reveal new information about how plates are deforming and hold the promise of new insight into the associated hazards and geologic formations. The key advances have been the discovery of episodic tremor and slip (ETS) and forearc basins interpreted as manifestations of megathrust asperities. The processes that govern ETS and potential relationships with major earthquakes remain unknown, yet these events have been proposed to be an integral part of the subduction process and may have an impact on the likelihood of earthquakes. Using new single-station methods to identify non-volcanic tremor and slow slip episodes over broader regions and time periods than previous studies, we compile an ETS catalog for the entire Cascadia subduction zone over the past 10 years. Correlated GPS and seismic signals are found all along the convergent margin, suggesting that ETS is an inherent part of the subduction process. The expanded dataset reveals 3 broad coherent zones with different recurrence intervals (11 mo, 14 mo, 19 mo), where the interval duration and zone boundaries correlate best with upper plate topography and geologic terrains. In particular, the recurrence interval appears to be related to rheology dictated by the overriding plate, as the zones with lighter, weaker, and more continental-like crust have shorter "hold times" between events. The 3 broad zones of common recurrence interval are further divided into segments by the phase of ETS events. The 6 largest (100-200 km) segments correlate with locations of fore-arc basins interpreted as manifestations of megathrust asperities, revealing new links between ETS and seismogenic behavior.

© Richard M Allen