Numerical simulations of the current channeling effect on MT responses due to shallow conductive structures

MT data obtained at an alluvial valley in Argentina showed a strong telluric current channeling along its axis. This effect was reflected in the MT curves as a very low response for the TM apparent resistivity for periods longer than 1 s. The cause of this channeling remained unsolved although the existence of shallow conductive structures may be related to this effect. The purpose of this work is to analyze in detail the magnetotelluric response of this kind of structures. The main objectives are to identify the relevant geometrical and electrical features that cause the anomalous TM response and to study the sensitivity of the MT modes to characterize this kind of structures. Starting from a previous 2D TE inversion, we modified the structure in order to reproduce the behavior of the MT curves. 2D and 3D forward modeling of different shallow conductive structures were carried out and synthetic data from related structures were inverted using the 2D RRI code.