The Influence of Surface Inhomogeneities On Deep Electromagnetic Soundings of the Earth

Abstract

Summary. Asymptotic expressions for components of the electromagnetic field of a grounded electric dipole are considered for the model consisting of a thin surface‐layer overlapping a stratified medium with a highly resistive screen on the roof. It is shown that the method of spatial derivatives makes it possible to obtain proper estimates of the impedance at distances of r≥|λ0| from the nearest edge of the surface anomaly (|λ0| being the effective depth of the field penetration in the underlying section). the magnetotelluric methods allow one to obtain the true values of impedance, provided r≥ max {|λ0|, |𝒻/(S−1+Z−0|1/2} where S is the integrated conductivity of the surface layer, 𝒻 is the transverse resistance of the screen, and Z−0 is the Tikhonov—Cagniard impedance for the medium underlying the surface layer. Copyright © 1987, Wiley Blackwell. All rights reserved