Preliminary residual magnetic map of the eastern Bering Shelf and parts of western Alaska

Residual magnetic anomalies for the offshore data were calculated by subtracting the Earth's main dipole field, adjusted for secular variations (based on the International Geomagnetic Reference Field (IGRF), epoch 1965, Fabiano and Peddie, 1969), from the observed values of the surveys listed below. The effects of diurnal variations and magnetic storms have been ignored. Individual marine magnetic profiles have been upward continued to an elevation of 1 km (Robinson, 1970; Henderson, 1970) on the assumption that the magnetic sources are two-dimensional in a direction normal to the ship's track. The upward continued profiles were computed by convolving each profile with an optimum (7, 15 or 30 points) upward continuation operator. Additional errors of unknown magnitude result from the use of two-dimensional analytic techniques in a three-dimensional field. However, on the average, values at crossings differ by only 10 percent.