On the use of line current analogues in geomagnetic depth sounding

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. Uses of a line current in a conducting half-space as a suitable analogue of the true induction processes are illustrated with comparison to 3 anomalies - a conducting block, Alert, and the Great Glen fault.-Author