By means of grounded electrodes and magnetometers, natural electromagnetic oscillations with a period from fractions of a second to a day or more are recorded. The apparent resistance of rocks in the studied cross-section is determined by the ratio of the amplitudes of electrical and magnetic oscillations. Due to the skin effect, the method makes it possible to estimate the change in rock resistance with depth. Based on the results of MTS, the subsurface structural relief of the basement or a similar high-resistance horizon at depths of up to ten kilometers is mapped. In addition, the distribution of the rock electric conductivity at significantly greater depths is studied.