Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya

Abstract

Understanding the geodynamics and seismotectonic characteristics of a region requires an integrated approach involving the analysis of structures, active deformations, seismicity, and tectonic stress conditions. Analysing the links between ongoing seismic activities and the development of the landscape provides a deeper understanding of the dynamic interplay between tectonic forces and geological formations. This study focuses on the Kullu-Larji-Rampur (KLR) window in the NW Himalaya, situated just south of the Main Central Thrust (MCT), where seismicity is notably frequent. The primary objective is to comprehensively analyse parameters in this region, located in Himachal Pradesh, India. Extensive fieldwork involved scaling and mapping active deformation and geomorphological features along major transverse routes of the Sutlej and its tributaries in Himachal Pradesh. Structural data collected encompass measurements of foliation/schistosity, lineations, bedding planes, fold hinge lines, limb of folds, axial planes, shear zones/planes, kinematic indicators, and more. Results from structural data, remote sensing data and field investigations indicate active footwall duplexing or faults along bounding surfaces of tectonic horses, including younger thrust splays within the footwall block of the Jutogh Thrust (JT) or within the KLR window. Additionally, the study assesses localized stress behaviour and seismicity parameters (b-value and source mechanisms) in this seismically active region using background seismicity. Notably, significant depth variations and anomalies in stress conditions are observed, interpreted as a brittle-semi-brittle and stress transition zone. The south-eastern section of the KLR window is identified as a high-stress accumulation zone. We have established a correlation between present-day seismicity and the evolving landscape of the region. The study concludes that continuous interseismic and co-seismic deformation, along with the active footwall duplex in the Lesser Himalayan Sequence (LHS), play pivotal roles in shaping the growth of the KLR window and driving active in-sequence thrusting along the younger splays of the Jutogh Thrust.