Geomechanics of Tectonic Stress Path Constraints and Outcrop Deformation Analysis of Naturally Fractured Rocks: A Case Study Along Main Boundary Thrust (MBT) and Nathia Gali Thrust (NGT), NW-Himalayas, Pakistan

ABSTRACT: Fractures are significant deformation-induced structural structures that appear in rocks under brittle conditions. Establishing a link between structural evolution and paleo stress orientations is thus required to provide comprehensive tectonic models for the studied region. The research region is located in the Lesser Himalaya (LH), which is bordered to the north by the Main Central Thrust (MCT) and south by the Main Boundary Thrust (MBT). The purpose of this work is to evaluate the fracture pattern in the rocks along the Main Boundary Thrust (MBT, NW Himalaya, Pakistan) and undertake paleo stress analysis. Fifty distinct circle inventories were made in the Beld, and 550 fracture orientations were seen and documented. The Win-Tensor application is then used to evaluate the fracture data for paleo-stress inversion. It is an interactive computer application for fracture analysis and paleo stress reconstruction that is based on the Right Dihedron Method. The findings show a compressive tectonic regime with r1 trending NNW–SSE. The Main Boundary Thrust (MBT) is thought to develop almost perpendicular to the direction of the highest primary stress orientation. 1. INTRODUCTION The geomechanics and mechanical properties of near-surface rock materials are significantly influenced by discontinuities, such as veins, fault frictional sliding, seismic characteristics, permeability, and fluid flow. Tectonic activity in the Earth's crust creates structural discontinuities such as faults, fractures, and joints. This work hypothesizes that the stress route influences rock deformation and failure, and establishing a link between structural evolution and paleo-stress orientations is critical for developing complete tectonic models (Allen et al., 1993). Paleo-stress studies are predicated on the idea that the direction of the highest shear stress should be the direction of the slide along the fault plane as shown in Figure 1. The stress ratio (R)= ((r2r3)/(r1r3)) and the three stress levels (highest (r1), intermediate (r2), and minimum (r3)) make up the outcome. There is an extensional stress regime (Normal Faults) if r1 is vertical and r2 and r3 are horizontal; a transpressional regime (strike-slip faults) if r2 is vertical and r1 and r3 act horizontally; and reverse/thrust faulting if r3 is vertical and r1 and r2 are horizontal (Anderson, 1905). Finding a connection between the paleo stress Beds and the later formation of the Himalayan MBT will enable us to ascertain the kinematics of the fractures associated with MBT and NDT, NW Himalayas, Pakistan. (Najwa et al., 2023).