Seismic Noise

The tectonic evolution of northwestern Canada spans several billion years of Earth history and presents an ideal environment for studying the processes of continental accretion and growth. We used ambient noise cross correlation to derive a new three‐ dimensional model of crustal shear wave velocity for the region (Dalton et al., JGR, 2011). Known sedimentary basins dominate lateral variations in wave speed in the shallow crust. In the middle crust, the model contains a strong low‐velocity region that correlates spatially with the location of Proterozoic metasedimentary rocks that have been inferred from active source reflection profiles to occupy much of the crust beneath the Cordilleran terranes. Velocity variations in the lower crust suggest a west‐to‐east transition from lower to higher wave speeds that aligns with the Cordilleran deformation front in parts of the study area.

 

We also investigated radial anisotropy in the continental crust of northwestern Canada from group-velocity curves of Love and Rayleigh waves obtained from ambient-noise cross-correlation (Dalton and Gaherty, GJI, 2013). The majority of best-fitting models contain VSH > VSV  (4–5 per cent) in the middle crust. The finding that the middle/lower crust is seismically anisotropic across a large swath of northwestern Canada, combined with recent observations of anisotropic crust in much of the western United States, suggests that anisotropy may be ubiquitous in the continental crust.

 

 

 

 

Seismic Noise

The tectonic evolution of northwestern Canada spans several billion years of Earth history and presents an ideal environment for studying the processes of continental accretion and growth. We used ambient noise cross correlation to derive a new three‐ dimensional model of crustal shear wave velocity for the region (Dalton et al., JGR, 2011). Known sedimentary basins dominate lateral variations in wave speed in the shallow crust. In the middle crust, the model contains a strong low‐velocity region that correlates spatially with the location of Proterozoic metasedimentary rocks that have been inferred from active source reflection profiles to occupy much of the crust beneath the Cordilleran terranes. Velocity variations in the lower crust suggest a west‐to‐east transition from lower to higher wave speeds that aligns with the Cordilleran deformation front in parts of the study area.

 

We also investigated radial anisotropy in the continental crust of northwestern Canada from group-velocity curves of Love and Rayleigh waves obtained from ambient-noise cross-correlation (Dalton and Gaherty, GJI, 2013). The majority of best-fitting models contain VSH > VSV  (4–5 per cent) in the middle crust. The finding that the middle/lower crust is seismically anisotropic across a large swath of northwestern Canada, combined with recent observations of anisotropic crust in much of the western United States, suggests that anisotropy may be ubiquitous in the continental crust.

 

 

 

 

Seismic Noise

The tectonic evolution of northwestern Canada spans several billion years of Earth history and presents an ideal environment for studying the processes of continental accretion and growth. We used ambient noise cross correlation to derive a new three‐ dimensional model of crustal shear wave velocity for the region (Dalton et al., JGR, 2011). Known sedimentary basins dominate lateral variations in wave speed in the shallow crust. In the middle crust, the model contains a strong low‐velocity region that correlates spatially with the location of Proterozoic metasedimentary rocks that have been inferred from active source reflection profiles to occupy much of the crust beneath the Cordilleran terranes. Velocity variations in the lower crust suggest a west‐to‐east transition from lower to higher wave speeds that aligns with the Cordilleran deformation front in parts of the study area.

 

We also investigated radial anisotropy in the continental crust of northwestern Canada from group-velocity curves of Love and Rayleigh waves obtained from ambient-noise cross-correlation (Dalton and Gaherty, GJI, 2013). The majority of best-fitting models contain VSH > VSV  (4–5 per cent) in the middle crust. The finding that the middle/lower crust is seismically anisotropic across a large swath of northwestern Canada, combined with recent observations of anisotropic crust in much of the western United States, suggests that anisotropy may be ubiquitous in the continental crust.