Speaker
Description
The Cascadia Subduction Zone (CSZ) is a convergent plate boundary stretching from Northern Vancouver Island to Northern California, following the coastline in the Pacific Ocean, separating the subducting Juan de Fuca Plate from the North American plate. The Explorer and Gorda subplates make up the northern and southern portions of the Juan de Fuca plate, respectively. The tectonic behavior of the northernmost part of this subduction zone is poorly characterized. A previous study was unable to find geodetically detectable slip accompanying tremor under northern Vancouver Island (Bartlow, 2020). By studying individual ETS events in more detail we have been able to detect slip accompanying tremor under northern Vancouver Island, but the amplitudes of both are small compared to those detected in southern Vancouver Island and the rest of Northern Cascadia. We can study the overall slip on the plate interface by isolating slow slip motion. Finding the slip occurring at the plate interface will constrain the direction and minimum rate of convergence of the Explorer plate. This study aims to characterize the apparent segmentation boundary seen in the tremor data between northern and southern Vancouver Island, which may imply slower subduction underneath northern Vancouver Island. This boundary is in proximity to the historical definition of the Nootka Fault Zone (NFZ) but is inconsistent with a recent study’s placement of the fault zone further north (Merrill, 2022). With the complexities of the region, episodic tremor and slip are a crucial part of understanding the tectonic setting under Vancouver Island.
