Geological and geomorphic evidences of neotectonic activity along the Himalayan Frontal Thrust, Nahan Salient, NW Himalaya, India.

In this paper, we report geomorphic signatures of neotectonic activity identified from the area around Nahan Salient along Himalayan Frontal Thrust (HFT), using remote sensing and field investigations. We document two newly discovered exposures of HFT fault zone and active fault traces along the mountain front at Khetpurali, Nahan Salient, NW Himalaya, India. We demonstrate that HFT fault zone at Khetpurali is not blind, instead it is exposed at the surface along with highly deformed, folded strata in the hanging wall and its geometry is quite variable with the possibility of along strike-segmentation. The geometry of fold and various deformational features preserved in the hanging wall indicate a process of fault-propagation-fold. This is in contrast to the previous observation of fault-bent-folding within the Nahan Salient. Two-three levels of river terraces are preserved and truncated in the hanging wall, along with the active fault scarps which are linked to uplift along HFT fault zone. The Khetpurali Anticline (KA), is a fault-propagating-fold formed due to displacement and shortening along HFT which dips 30° towards north and strike WNW-ESE. The uplift (U) along the KA is calculated to be ~73 m and accommodated 7.3% shortening of the original length, before the fault tip truncated the fold. Various deformational structures have been identified within the hanging wall around-tip damage zone of ~80 m perpendicular to HFT fault zone and in the core of KA. Northwest of Khetpurali, a south-facing hogback structure ~100 m high is formed due to erosion of forelimb of the anticline. At Khetpurali, tectonic control due to folding of strata and uplift of river terraces is evident as the Dudhgarh River forms V-shaped profile near the thrust, compared to the wide floodplain before and after crossing the HFT fault zone. Along strike segmentation of HFT and associated anticlines is observed as the surface trace of HFT is offset at Khetpurali, Trilokpur, and Sabilpur due to the strike-slip faults. The study reveals that HFT has been truncated by tear faults and has different subsurface geometries in study area which may have implication on seismic hazard in the Nahan Salient where three thrusts; Himalayan Frrontal Thrust (HFT), Nahan Thrust (NT) and Main Boundary Fault (MBF) are located at relatively shorter distance of ~6 km as compared to the surrounding recesses. [ABSTRACT FROM AUTHOR]