Two-station Rayleigh wave Tomography of Canada.

Seismic tomography is a common method used to study the lithosphere which records evidence of past and present tectonic processes. In largely aseismic areas such as central and eastern Canada, single-station measurements of surface-wave dispersion will provide limited and uneven resolution; two-station measurements, in principle, provide coverage limited only by station distribution. This work examines seismic velocity and anisotropy variations of the Canadian lithosphere using two-station-based surface-wave tomography, to obtain new insights into the formation history of the continent.

A cross-correlation method was used to obtain new two-station dispersion curves which were added to an existing data set. These were chosen to fill in gaps in ray coverage and to maximize azimuthal distribution, particularly across the Prairies and the Cordillera. Tomographic inversion was used to calculate anisotropic phase velocity maps for periods of 15-400 s, following outlier exclusion and resolution testing.

The phase velocity maps show that the low velocity Cordillera contains two zones (west and east) with different anisotropy, and exhibits a sharp eastern boundary with the Canadian Shield, which shifts eastward near the US border. The highest velocities are seen beneath the craton, with particularly high velocities in Nunavut (northern Canada) and the western Superior Province. A clear distinction between the Shield and the lower velocity Appalachian domains is also noted.