Physical interpretation of the distortion of magnetotelluric response

Purpose This study aims to understand the physical processes that occurs at the contact of conductivity-contrasting media responsible for the distortion of the measured magnetotelluric response. Design/methodology/approach A two-dimensional (2D) model of a resistive half-space and an adjacent conductive layer embedded therein was first investigated. It was theoretically shown that at their vertical contact, an incident electromagnetic wave activates processes that lead to disturbances of the original fields – Coulomb action and current induction. To generalise this knowledge, a three-dimensional (3D) model of a layered half-space with several different interfaces was designed. Key to its construction was the mathematical demonstration that the undisturbed apparent resistivity is the result of the convolution of the electric field and the inverse function of the magnetic field passing through the individual layers. Findings Theoretical analysis led to the creation of computational programs for calculating transfer functions in 2D and 3D situations for a wide frequency range. The distortion of the synthetic response thus obtained was discussed mainly in connection with the undesirable phenomenon of static shift in the measured data. It was shown that the static shift is a manifestation of the asymptotic behaviour of solutions at large periods, which is consistent with observations. Originality/value Understanding the patterns of behaviour of disturbance quantities and their expressibility in the form of standard mathematical functions gives the prospect of developing a method for eliminating their manifestations, first from synthetic and later from real field data.