Influence of a Step-Shaped Mountain Relief on the Results of Magnetotelluric Soundings

The objective of the study was to assess the influence of the relief, defined in the form of a system of steep scarps, on the apparent resistivity curves and the parameters of geoelectric sections determined from them during magnetotelluric observations. It was solved using three-dimensional mathematical modeling of magnetotelluric fields using the finite difference method and the Maxwellf program. The dependences of the curves and the results of their one-dimensional inversion on the parameters of the blocks that make up the two- and three-dimensional models were analyzed. The distortions that shift the invariant curves of apparent resistivity calculated on the steps of the staircase model from the MTS curves measured on the plane ground-air boundary were estimated. In this case, the geoelectric parameters of the blocks located under the plane boundary are equal to those specified under the model with relief. The problem of constructing geoelectric models in conditions of stepwise changes in terrain can be solved using three-dimensional mathematical modeling of apparent resistivity curves, adjusted by normalizing coefficients that take into account the transition to a 3D model with a plane ground–air boundary. However, they depend on the period of variations. For this reason, it is more appropriate to evaluate the use of 3D inversion programs that include terrain topography in the initial 3D models. Before carrying out this procedure, it is necessary to know what shifts the apparent resistivity curves may have if the influence of the relief on them and the deviations obtained during their inversion of the geoelectric parameters of the sections from the test models are not taken into account.