Influence of "geologic noise" on magnetotelluric-sounding data and methods for taking it into account

The paper deals with the problem of interpreting magnetotelluric data in the differentiated low-conductivity upper part of the section. An observation network often makes it impossible to describe a spatial irregularity spectrum completely, so, using 3D data inversion comes across a significant spatial equivalence of the solution. The effect of irregular conductivity of the upper part of the section at one of the sites is considered by the comprehensively studied near-field transient electromagnetic sounding in dense 3D networks. A technique is proposed for choosing the directions of the minimum gradient of anomaly-causing conductivity and for selecting corresponding quasi-longitudinal curves for estimating the deeper parameters of the model. The advantage of using quasi-longitudinal curves is shown, and the high geological efficiency of the developed technique for interpreting magnetotelluric data is demonstrated at one of the sites of the Siberian Platform.