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Geomagnetic depth-sounding profile across central British Columbia Dragert, Herb

Abstract

Geomagnetic depth-sounding was carried out in a large-spaced profile across central British Columbia in order to map the conductivity structure of the crust and upper mantle in the central Canadian Cordillera. Geomagnetic variographs were set up from east of Jasper to Prince Rupert in two successive east-west profiles during the summer of 1969. Numerical analysis of geomagnetic storm activity indicates that the discontinuity in the attenuation of the vertical magnetic field, as first reported for south-eastern British Columbia by Hyndman (1963), is located in the area of the Rocky Mountain Trench. All stations to the west exhibit typical 'low Z' characteristics and no or little anomalous induction; stations to the east of the trench display a strong, high-frequency Z-variation content as well as anomalous field enhancement. Power spectral and polarization analyses show a first order agreement with the two-dimensional conductivity structure model proposed by Caner (1970) for south-western Canada. Second-order effects suggest a more complex model consisting of two conductivity discontinuities: One shallow structure strikes roughly NW-SE at a depth of 10 to 15 km. and may be associated with the 'edge' of a hydrated layer located at the western front of the Rocky Mountains; a second much deeper structure, trending approximately E-W, is located south of Kootenay Lake and is possibly associated with a strike-slip feature in the upper mantle (Lajoie and Caner, 1970).

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