抄録
Two unusual features of geomagnetic variations have now been discovered in the Arctic Archipelago of Canada. The first anomaly at Alert on Ellesmere Island is characterized by abnormally high levels of irregular magnetic activity and a persistent directional characteristic of the vector horizontal disturbance. An adequate iono-spheric explanation has not been found. Recent papers have given an explanation of the gross characteristics of the Alert magnetograms in terms of induction in a large anomalous conductor in the upper mantle striking parallel to the channel separating north Ellesmere Island from Greenland. Field experiments followed by simple potential and spectral response analyses confirm the existence of a gross conductor. In this paper the uncertainties in and shortcomings of the first-order explanation and minor modifications are stressed, and an alternative solution involving induction in the conducting mantle and a highly conducting circuit examined. The alternative solution appears to be even more inadequate.
The second anomaly at Mould Bay, Prince Patrick Island, is characterized by the striking absence of shorter-period vertical field magnetic variations. Assuming the presence of a sheet conductor at depth it has been estimated earlier from the frequency dependence of the power spectrum that a 10-20km thick layer with a conductivity near 1011emu is required near the bottom of the crust or in the upper mantle. The assumptions in deriving this explanation are outlined, and theoretical curves shown which demonstrate that the neglect of reasonable conductivity above and below the anomalous layer appears justified. Results are shown applying the same technique to plane earth induction in a non-anomalous area, and to one magneto-telluric situation of current interest.
