A seismic refraction profile approximately 700 km long, from Greenbush Lake, British Columbia to Swift Current, Saskatchewan along latitude 50° 30′ is studied with the aid of delay time solutions. Additional refraction data in an area of large gravity anomalies southeast of Calgary, Alberta is included. The analysis indicates that upper crustal velocities vary laterally from 6.1 km/s to 6.5 km/s and that the boundaries between the velocity zones are most probably near vertical faults which involve the whole crustal section through to the Mohorovicic discontinuity.Upper mantle velocities vary along the profile from about 8.0 km/s west of the Rocky Mountains to 8.3 km/s in the region between Vulcan and Suffield where the profile crosses the Sweetgrass Arch. The data indicate a crustal root under the Rocky Mountains of about 5 km thickness.Comparisons between observed Bouguer gravity anomalies and those computed for the seismic model are used as a further constraint on the interpretation of the seismic data and a good fit is obtained when the initial seismic model is adjusted within the limits of the seismic control.

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