Time variations of the geomagnetic field observed across British Columbia at a mean latitude of 54 °N are analyzed using 'single-station' and 'paired-station' optimum transfer functions. The frequency and spatial dependence of both coastal and inland geomagnetic anomalies are estimated with the following results. (1) The normal coast effect is strongly perturbed by lateral conductivity inhomogeneities both north and south of the profile. (2) A simple, single NW–SE striking conductivity contrast between the Cordillera and plains cannot account for the total geomagnetic anomaly in the area of the Rocky Mountain Trench; a three-dimensional model is required, incorporating (i) a lateral inhomogeneity striking east–west and located to the south of the profile, (ii) the effect of induction by the vertical component of source or secondary fields.

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