Abstract

First three dimensional (3D) geoelectrical model of Sub-Himalaya, Uttarakhand region has been presented. The model is obtained by 3D inversion of 22 sites Broad Band Magnetotelluric (BBMT) data recorded from the region. Investigated region extends from Indo-Gangetic Plane (IGP) in south to the Lesser Himalayan region in the north and crosses two major Himalayan thrusts: Main Frontal Thrust (MFT) and Main Boundary Thrust (MBT). MATLAB based AP3DMT code (Singh et al. 2017) has been used for this purpose. The motivation for applying 3D inversion to the MT data is that no assumption about the geoelectric strike direction is needed and the investigated sites need not be projected along a 2D profile line. To keep the optimum computation time, we have selected full impedance tensor at 49 periods in range from .002 to 541 s for 3D inversion. The 3D geoelectrical model of the region demonstrates better resolved resistivity features specially, in shallow depth (< 10 km). Shallow conducting features (< 10 ?m) are associated with Piedmont fault (PF), MFT and MBT. Southern region represented by a low resistivity (< 50 ?m) zone at shallow depth (5-7 km). Geologically this zone representing the loose sediments of the Indo-Gangetic Plains (IGP) whose thickness increases in the south. Highly resistive (> 500 ?m) layer below the IGP sediments is the basement rock, representing the resistivity of top of the subducting Indian Plate. The model is may be used to constrain geodynamical model of the region and may be further improved by increasing data density.