Transverse Tectonics Structures in the Garhwal Himalaya Corridor Inferred from 3D Inversion of Magnetotelluric Profile Data

Abstract

In the Garhwal Himalayan Corridor (GHC), we recorded the magnetotelluric (MT) data at 40 sites, in three phases. Out of these 40 sites, useful tipper or vertical magnetic field transfer function (VTF) data was available only at 19 sites. The resistivity model, obtained from 3D inversion of the MT data, is used to investigate the existence of transverse tectonic structures in the Garhwal Himalaya. Through a synthetic inversion experiment on scattered data over a profile, like our GHC profile, we have demonstrated that the MT data can be used to qualitatively infer about the off-profile resistivity structures within about 20 km from the profile. We carried out several 3D inversion experiments using different subsets of full impedance tensor and VTF responses individually and jointly to arrive at the final resistivity model. The 2D profile section of our 3D resistivity model explains the thrust tectonic and flat ramp flat geometry of the Main Himalayan Thrust (MHT). Furthermore, the inverted model delineated Delhi–Haridwar Ridge (DHR) as a highly resistive (> 1000 Ωm) feature beneath the low resistive (< 50 Ωm) sediments of the Indo-Gangetic Plain (IGP). The DHR continues up to the Inner Lesser Himalayan region, and it is bounded by two conductive (< 10 Ωm) fluid-saturated fractured zones situated off-profile, and these run nearly parallel to the DHR. From the electrical image of the DHR and of the associated conducting feature, which have the geoelectric strike of N13°E, we inferred that these features are transverse to the main Himalayan arc.