The influence of surface inhomogeneities on deep electromagnetic soundings of the Earth

What is it about?

To investigate the effect of subsurface heterogeneities on the estimates of the Tikhonov-Cagniard's impedance, we consider a model consisting of a non-uniform sub-surface conductive layer, underlain with a laterally uniform resistive layer and a 1D deeper structure. It is shown that the effect of heterogeneities on the MT-impedance found from the electric and field data propagates along the so-called "adjustment distance", which may be by far larger than the depth of the field penetration into the ground. The same impedance may be determined using only the magnetic field data using "method of spatial derivatives", which is affected by the heterogeneities along a distance of the order of the field penetration depth. Mathematically the conclusions are based on the asymptotic expression derived for the field of an electric dipole place in the sub-surface conductive layer.

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Why is it important?

The paper explains the nature of the distorting effects of the sub-surface inhomogeneities on estimates of the earth structure impedance.