Three dimensional topography correction of the magnetotelluric data

Magnetotellurics, being one of the passive electromagnetic method, have been successfully deployed in many hilly regions such as Himalayas. The other active geophysical methods (seismic, active EM) faces difficulty in setting up the survey, hence they are hardly adopted in the hilly terrain. Topographic variations due to irregular surface terrain distort the resistivity curves and hence may not give accurate interpretation of magnetotelluric data. Due to rugged topography current flow is focused in valleys and diverge under a hill. As a result of this the equipotential surface are distorted producing anomalies. Topographic distortion is much more important, when we are considering for geothermal and mineral exploration. In this paper, we have simulated the 3D topography model using finite difference method based algorithm. Further, we adopted distortion tensor stripping off technique and proposed topographic correction of the MT data with 3D assumptions. Different cases are discussed which show that the topographic effect depends on the slope angle and elevation of the topographic feature. Later, this new approach is applied to correct the real data from Sikkim Himalaya, which brought out the true nature of the basement in this region.


Figure: (a) Two layered 3D trapezoidal hill model with conductive dyke ‘A’ of 10 ohm.m in a layered medium with first layer of 100 ohm.m and second layer with 1000 ohm.m. (b) MT response of the model along a profile at 1 Hz frequency.


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Sushil Kumar, Prasanta K. Patro, B.S. Chaudhary, Three dimensional topography correction applied to magnetotelluric data from Sikkim Himalayas, Physics of the Earth and Planetary Interiors, Volume 279, 2018, Pages 33-46.