Effect of Himalayan topography on two-dimensional interpretation of magnetotelluric data

Magnetotelluric method is a powerful tool for deep crustal studies of tectonically active mountainous regions such as the Himalaya, where logistic constraints severely limit the use of other artificial source electrical and electromagnetic methods. Topographic variations in mountainous regions distort apparent resistivity curves and thus lead to artefacts in interpreted models. In the present work, we have analysed a simplified two-dimensional (2D) model of the subsurface electrical resistivity structure along a profile in the Garhwal Himalaya for the effect of topography. The topography varies significantly along the profile between the foothills and the higher Himalaya. We first computed TE and TM-mode apparent resistivity and phase curves at various stations along the profile for a model with topography and then inverted these datasets for two cases. In the first case the surface of the earth was assumed to be flat, whereas in the second case the actual topography was included in the model. The results suggest that the interpreted model assuming flat earth is similar to the one obtained by including topography in the model. Inclusion of 10% Gaussian noise to the synthetic data does not change these results. Thus, we infer that the effect of 2D topography is not prominent in the 2D interpretation of the selected Garhwal Himalaya profile.