The problem of ``current channelling'': a critical review
Alan G. Jones
The notion that currents induced 'elsewhere', by external source fields, could wend their way in a
frequency-independent ohmic-like manner through a region of interest has been the cause of many recent
disputes within the geomagnetic induction community. In particular, two-dimensional (2D) models of the
Rhinegraben, and of the region known as the 'Eskdalemuir anomaly' in southern Scotland, have been
dismissed as erroneous by those who believe that the observations are more correctly interpreted as due to the
effects of 'channelled' currents rather than 'induced' currents. In this review, attention is paid primarily to
consider under what circumstances any perturbation of current flow, which may manifest itself as a 'DC-like'
channelled current, could cause a 'problem' for those wishing to interpret their observations. Various
concepts are introduced, particularly the ratio of 3D/2D current channelling numbers for the induction
problem, which is shown to be the ratio ofthe length of the 3D body to the skin depth in the host medium. It is
stressed that the worker must analyse his data by adequate statistical techniques, and that the simplest
physical models possible, that describes the observations, must be sought. Finally, suggestions are made for
further work to be undertaken.
Geophysical Surveys (now Surveys in Geophysics), 6, 79-122.
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Alan G Jones / 28 February 2010 /