Topography distortion effect on Magnetotelluric (MT) profiling of Sub-Himalayan region using two-dimensional modeling

Abstract

In order to correctly understand the earth's subsurface resistivity structure, it is vital to take into account and analyze topography influenced magnetotelluric (MT) data. To compute MT responses (impedance, apparent resistivity, and phase) over undulating topography, a Finite Difference Method (FDM) based algorithm is modified. The modified algorithm was tested using models that have already been published in the literature, and MT responses were computed for both TE and TM mode at various periods. While there are certain discrepancies resulting from discretization approaches, the computed and reported results are generally in worthy agreement. It has been noted that the electric current flowing across and along the strike direction causes the TM-mode responses to be more distorted than TE-mode responses. A synthetic investigation of topography's impact on MT data also takes into account 2D inverted geoelectric model from the Garhwal Himalaya region that is based on field data. MT responses are computed over a range of periods between 0.001 - 121 seconds on topography and flat earth surface. Along the Roorkee-Gangotri profile at 32 sites, the distortion effect in MT data caused by the complex Himalayan topography is examined at six different time periods. It has been shown that distortion effects in MT data are most pronounced at low periods .  The sites that are at or near hilltops and in valleys have more distorted MT responses, as evidenced by the relative errors analysis between topography and flat earth responses.

URN:NBN:sciencein.jist.2023.v11.462