Publication 24

On the use of line current analogues in geomagnetic depth sounding

Alan G. Jones


Various workers have appealed to Biot-Savart's law for interpreting their anomalous geomagnetic response functions as an aid to describing the electromagnetic induction process. This approach, of using such a line current analogue, is shown herein to be erroneous if the conductivity of the lower half-space is not taken into consideration. A numerical solution, using an FFT, is derived from the kernels of the electromagnetic field components involved, and is compared with the simplistic solution offered by Biot-Savart's static field approximation. It is shown that within a close proximity of the surface position of the buried line current, Biot-Savart's law is reasonable. However, outwith this distance the anomalous magnetic field components, and accordingly their ratio, cannot be described by Biot-Savart's law, but closely resemble induction, at the inductive limit, in an isolated well-conducting inhomogeneity. Uses of a line current in a conducting half-space as a suitable analogue of the true induction processes are illustrated with comparison to three anomalies - a conducting block, Alert, and the Great Glen fault.


Journal of Geophysics (Zeitschrift fuer Geophysik), 60, 56-62.

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Alan G Jones / 28 February 2010 /