Abstract
Coastal British Columbia, 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 and North American
plates. Further landward, the crust of the North American plate is made
up of several geologically unique 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) recorded at stations
across western coastal British Columbia including northern Vancouver
Island and southeastern Alaska. Using these receiver functions, 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 provides insight into
the evolution of the margin and surrounding region, as well as the
tectonic processes currently taking place. Identification of the dipping
interfaces associated with the subducting Pacific and Juan de Fuca
plates is important for assessment of earthquake and tsunami hazards.