Subduction zone structure and episodic tremor and slip in Cascadia

Speaker: Pascal Audet

Department of Earth and Environmental Sciences, 

University of Ottawa

Geological evidence suggests that the Cascadia subduction zone offshore western North America will likely rupture in a giant magnitude 9 earthquake within the next few centuries and produce a large tsunami. Despite the current paucity of earthquakes in Cascadia, a recently discovered phenomenon called “episodic tremor and slip”, or ETS, indicates that the fault periodically releases accumulated tectonic stress during week-long ruptures at depths of about 30-40 km. At those depths the oceanic crust undergoes metamorphic reactions that generate free fluids and the megathrust fault likely becomes a thick shear zone. My work focuses on illuminating the geological conditions that exist in the vicinity of the ETS source region using seismic data to understand their role in the earthquake cycle. This work indicates that the fluid budget (production, circulation and storage) is critical in generating ETS.