This study investigates the influence of stepped topography with relief amplitudes of 1–3 km on magnetotelluric (MT) estimates of subsurface resistivity structure. The analysis is based on 3D finite-difference forward modeling of MT responses. The invariant parameters of the impedance tensor calculated for models with stepped topography are compared to their counterparts in the models with a flat air-ground interface. Based on the comparison, MT data distortions caused by surface topography are estimated. The dependence of apparent resistivity curves calculated on upper and lower benches of the step on the parameters of geoelectric section is analyzed. Modeling results show that, when analyzing deep parts of the geoelectrical structure, invariant apparent resistivity curves from both the upper bench (the plateau) and the lower bench (basin, or trough) require correction if the observation sites are formally referenced to a flat air-earth interface. The findings emphasize the need to explicitly incorporate topography in 3D MT inversion to avoid interpretation bias.
Belyavsky et al. (Wed,) studied this question.