Publication Date:
1974-01-01
Description:
In 1963, 1964, and 1970 geomagnetic variations in 3 components were measured at 14 sites in the Western Arctic Islands of the Canadian Archipelago. The suppression of Z amplitudes, first observed at Mould Bay, is now confirmed to extend from Mould Bay south to Holman Island, a distance of 620km, and from McCormick Inlet to Houghton Head, an east-west distance of 292 km. Spectral decomposition of many component time series gave mean Z/X energy density ratios which fall into two groups. One group (anomalous) is characterized by slopes of 2, with attenuations of 10-50 between the 60 (or 100) and 10 min energy ratio estimates. The other group (non-anomalous) do not display such behaviour in the component ratio plots. At periods near 10 min the energy ratios of the two groups differ by factors of 5 to 10. Distributions of Parkinson vectors for various period intervals support in part a deep conducting body and in part electric currents in salt water channels or deep ocean. Coherency analysis of horizontal components between stations supports the assumption that external source dimensions are proportional to the 1/3 power of period of disturbance. However, the electromagnetic theory of induction for horizontal layered models of infinite extent has failed to explain the observed reduction of Z amplitudes near 10 min periods. Long period (100-300 min) energy ratio estimates are explained as the effect of a conducting (1 S/m) layer or half-space in the upper mantle underlying most of the Western Arctic. Love-wave model studies have detected a low-velocity zone in the upper mantle between Mould Bay and Coppermine. © 1974, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.
Print ISSN:
0022-1392
Topics:
Geosciences
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