IMAGING THE LITHOSPHERE OF WESTERN CANADA WITH AMBIENT NOISE DATA

Abstract

The Canadian Cordillera represents a key transition zone from the present-day Pacific plate boundary, through the tectonically active Phanerozoic Cordilleran orogen, to the stable Precambrian craton of North America. This thesis uses ambient noise tomography to image the geometry of lithosphere across the Cordillera-craton transition with improved spatial resolution. More than six thousand day-long vertical-component seismic waveforms from over one hundred broadband seismic stations were analyzed across western Canada. Rayleigh wave phase velocity maps were generated for periods from 6.0 to 60.0 s. These maps were supported by uncertainty estimates, velocity perturbation maps, and inversion convergence results. The period-dependent phase velocity information was further used to develop shear wave velocity (Vs) depth slices at 10, 20, 30, 40, and 50 km depth.The results show strong lateral velocity variations across western Canada. At shorter periods, the phase velocity maps mainly reflect shallow crustal heterogeneity, including sedimentary basin effects and upper-crustal variations. At intermediate and longer periods, the contrast between the Cordillera and the craton becomes more pronounced. The Vs depth slices further show that this contrast strengthens with depth. Low Vs values beneath the Cordillera indicate warmer, thinner, and more deformed lithosphere, whereas high Vs values beneath the craton reflect colder, thicker, and more stable lithospheric mantle. Overall, this study provides higher-resolution seismic images of the lithosphere beneath western Canada through Rayleigh wave phase velocity maps and Vs depth slices. The result of the study area helps constrain the geometry of the lithospheric transition and provides a basis for future studies integrating seismic, thermal, and tectonic observations across western Canada.