Subsurface Resistivity Image of Sikkim Himalaya as Derived from Topography Corrected Magnetotelluric Data

Abstract

Abstract The Sikkim Himalaya is the eastern division of the Himalayan arc and is located between the Nepal and Bhutan Himalaya. Due to the complex geology, the abnormal trend of Main Central Thrust (MCT) and duplex structure in Higher Himalayan Crystalline (HHC) zone, the magnetotelluric (MT) data in Sikkim Himalayan region is modeled using topographic correction. In the present research, the three-dimensional (3-D) topographic correction using impedance tensor correction algorithm was applied to eight sites from the Sikkim Himalayan region and then inverted on the flat terrain. This paper presents the effectiveness of the 3-D topographic correction on two dimensional (2-D) modeling by comparing inversion models (a) model with distorted data on flat terrain, (b) distorted data with topography, (c) 3-D topography corrected data on flat terrain, to mitigate the effects of topography in MT data. The major outcome of the present study is in the form deciphering much bigger dimension in case of topography corrected data of the overlying resistive block (~9000 ohm.m) having depth up to 15 km between the sites Manglay and Lema, which correlate with the exposures of the Daling Formation in the northern Lesser Himalayan Sequence (LHS) and Lingste granite in the MCT zone. The topography corrected MT data brought out the topography of the resistive Indian crust more clearly.