Crustal seismic anisotropy along the continental margin in western Canada from receiver function analysis

Abstract

Coastal British Columbia (BC), Canada, has the highest seismic hazard in the country due to convergent and transpressive deformation at offshore plate boundaries between the Pacific, Juan de Fuca (JdF) and North American (NA) plates. Further landward, the crust of the NA plate is made up of several geologically unique exotic terranes and is unusually thin. Investigating the geophysical features in this area can help us better constrain its tectonic history and the geophysical processes that are currently underway. Here, we conduct an analysis of teleseismic body-wave scattering data (i.e., receiver functions [RFs]) recorded at stations across western coastal BC including northern Vancouver Island and southeastern Alaska. Using these RFs, we perform a harmonic decomposition with respect to earthquake back-azimuths to determine the orientation of seismic anisotropy over a series of depth ranges, attributable to either mineral alignment or dipping structures. We find a coherent pattern of margin-parallel orientations at upper crustal depths that persist onto the mainland at distances 420 km from the margin. Furthermore, dominant receiver function orientations at depth are attributed to dipping faults and interfaces, and fabrics due to lower crustal shearing or inherited from tectonic assembly along the margin. This work supports models for the tectonic assembly of this region that involve a combination of plate subduction and transpressive motion along crustal scale faults that pervade a wide portion of the margin. This work also helps to constrain the current geometries of the subducting Pacific and JdF slabs.

Taylor Tracey Kyryliuk

PhD Candidate

My research interests include geophysics, marine seismology, slow earthquakes, tectonics, signal processing and software development.