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The structure of the earth's crust in the vicinity of Vancouver Island as ascertained by seismic and gravity observations White, William Robert Hugh

Abstract

A seismic explosion program has been carried out in the Vancouver Island-Strait of Georgia area of Western Canada. The program included a relatively-intensive survey in the Strait of Georgia between Campbell River and the south end of Texada Island, as well as a number of longer range refraction lines extending from Kelsey Bay along the coast as far south as northern California, and east through the mountains to a distance of 700 km. Gravity readings were obtained at intervals of about ten km. along the east coast of Vancouver Island as well as for a number of east-west traverses. Readings were also obtained for a few locations on the British Columbia mainland. Except for a marked positive trend in the Victoria area, the regional value of the Bouguer anomaly for the Vancouver Island area is nearly zero. The average structure for the area, derived from the seismic refraction observations consists of a layer of volcanic and granitic strata less than five km. in thickness, and an intermediate layer with a constant velocity for compressional waves of 6.66 km/sec, 46 km. thick. A velocity of about 7.7 km/sec. for the mantle has been observed along unreversed refraction lines, both along the coast and east through the mountains. Interpretation of the refraction observations has been based mainly on first arrival phases. The observed regional gravity anomaly is compatible with the crustal model obtained from the seismic results.

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