Distortions of impedance and tipper tensors due to three-dimensional perturbations of the earth and field

Magnetotelluric (MT) sounding measurements are conducted, as a rule, along a single profile or mutiple profiles, and data are interpreted using 1D and 2D earth models. In a real situation, the earth is three-dimensional, and the primary field may vary laterally. This implies that 1D and 2D inversions of MT data contain some error, up to the appearance of false structures. In this study, analytical methods are used to obtain expressions for the effect of small deviations of the earth and the primary field from the Tikhonov–Cagniard model on the impedance and tipper tensor components (sensitivity functions which determining the size of the zone near the sounding point within which the perturbations affect the impedance and tipper at this point).