Onshore/Offshore Shear-Wave Velocity Structure Along the West Coast of British Columbia from Surface-Wave Tomography

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

The west coast of British Columbia, Canada, consists of active tectonic boundaries including the northernmost extent of the Cascadia Subduction Zone (CSZ) as well as the Queen Charlotte Fault (QCF) zone. Off the coast of Vancouver Island, seismicity is associated with the Explorer and Juan de Fuca ridges, as well as with convergence in the CSZ, which has the potential for producing large (M9.0) megathrust earthquakes. Further north, the transpressive interaction between the Pacific plate and the North American plate results in significant seismicity along the west coast of Haida Gwaii, including both strike-slip and thrust events. This research investigates the onshore/offshore tectonic structure of the west coast of Canada (from southern Vancouver Island to northern Haida Gwaii) using surface-wave tomography. In this work, Rayleigh-wave dispersion is estimated from regional earthquakes recorded primarily on Canadian National Seismograph Network (CNSN) stations, supplemented by short-term station deployments from various sources (e.g., POLARIS, IRIS-PASSCAL). Some of the CNSN stations have recorded decades of data, and several hundred events. We consider a new direct Bayesian (probabilistic) inversion method to estimate a posterior probability density (PPD) of parameters that describe a three-dimensional shear-wave velocity model for the region. The velocity structure and associated uncertainties are estimated from properties of the PPD. This work provides constraint on the variations in offshore tectonic structure along the west coast of Canada and may help explain the complex processes occurring in the region.

Presenting Author: Jeremy Gosselin

Authors