Geomorphometric Appraisal for Seismic Hazard Assessment in the Chenab River Basin of the NW Himalayas, India

The present research emphasizes to delineate the active tectonic features in the Kashmir Himalaya by quantitatively analysing the Chenab River basin (CRB) of the NW Himalayas. Within the CRB this study focuses on the Late Quaternary tectonics of the Kishtwar window (KW) which is an oval-shaped structure comprised of Higher Himalayan Crystalline (HHC) and enclosed by the Main Central Thrust (MCT). The tectonic activity of the Kishtwar fault (KF) since Early Quaternary is known based on structural and kinematics data along with seismic clustering and geomorphic expression of the fault all along the valley. However, active fault segmentation along KF is still unknown. In the present study, we identified several morpho tectonic landforms associated with KF. We observed several geomorphic expressions such as Sackungen (back hill facing fault scarp), stream offset, sagponds, strath terraces and related to active movement along KF. Based on displaced sedimentary units and stratigraphic contacts we identified KF as a high angle reverse fault across the MCT. Besides this, based on the geomorphic attributes and faulted Quaternary sequences it is confirmed that the KF is active during the late Holocene period. The Stability Index Analysis (SIA) suggests that approximately 13.38% area of the CRB is stable, 12.24% is moderately stable, 25.32% moderately vulnerable, 29.57% area is vulnerable and similar to 19.03% area is highly vulnerable to earthquake hazard. The Gradient Length Anomaly (GLA) analysis of three major active zones: (i) the zone between Reasi Fault (RT) and Main Boundary Thrust (MBT); (ii) the Kishtwar window zone; (iii) the upper catchment zone of Chenab around Keylon have been identified. The normalized Steepness Index (K-sn) variation along the longitudinal section of the Chenab River basin shows an anomalous increase in the glacio-fluvial transitional processes. We observed the interplay of lithology, relative thrusts activity, climate and anthropogenic activity during the Holocene period affects the present-day steepness of a river channel and provides it a specific shape. The lower values of observed downstream in the case of the Chenab Basin have more strength to achieve dynamic equilibrium as compared to its upstream counterpart. Lithology and tectonics give the impression to play an important role in influencing erosive strength. The weaker lithology which favored denudation and active tectonics on the other hand within the Chenab Basin led to the rise in gradient to enhance erosion of sediments. Moreover, our analysis suggests that the presence of knickpoints toward the upstream are formed because of glacial activity while at downstream the influence of litho-tectonic transition is more prevalent.