Influence of Benched Mountain Relief on the Results of Magnetotelluric Soundings

The aim of the conducted research was to estimate the influence of the relief, specified as a system of steep benches, on the apparent resistivity curves and the parameters of geoelectric sections determined from these curves during magnetotelluric observations. It was solved using three-dimensional mathematical modeling of magnetotelluric fields by the finite-difference method using the Maxwellf program. The dependences of the curves and the results of their one-dimensional inversion on the block parameters of the two-dimensional and three-dimensional models were analyzed. Distortions that shifted the invariant apparent resistance curves calculated on the steps of the staircase from the MTS curves measured at the flat ground-air boundary were estimated. At the same time, the geoelectric parameters of the blocks located under the flat boundary are equal to those specified under the model with the relief. The problem of constructing geoelectric models under 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 flat ground-air boundary. However, they depend on the period of variations. Due to this, it is more appropriate to evaluate the use of three-dimensional inversion programs that include terrain topography in the starting three-dimensional models. Before carrying out this procedure, it is necessary to know what displacements of the apparent resistivity curves may occur if the influence of terrain and deviations obtained during their inversion, as well as geoelectric parameters of sections from test models are not taken into account.

magnetotelluric sounding, geoelectric sections, terrain relief, distortion coefficients