Identifying reactivation zones in the kotrupi landslide through UAV, satellite image and slope stability analysis

August 2017. Since then, the site has experienced repeated reactivations. This study integrates UAV mapping; satellite image analysis; field investigations; and numerical simulation, to evaluate the landslide reactivation and slope stability. TanDEM-X (10 m) and UAV derived DEMs (Digital Elevation Model) were used for establish the pre and post event boundary conditions for stability assessment. Seven representative profiles were selected to characterize the deformation regime and analyze the reactivation potential zones. The Factor of Safety (FoS) was estimated using the Limit Equilibrium Method (LEM) and maximum displacement values inferred using a Finite Element Model (FEM). The results indicate that the right flank exhibits the lowest FoS values, ranging between 0.35 and 0.5 making it highly susceptible to reactivation. In contrast, the left and central portions are comparable stable, as these portions have relatively higher FoS. However, all seven profiles have FoS values lower than 1, indicating overall slope instability. Satellite image analysis further conformed the progressive reactivation if the right flank, whereas the left flank remained comparatively stable over time. Extensive field surveys were conducted to collect geological, geotechnical, and hydrological information. The dataset consists of rock orientation, fault mapping, joint planes, tension crack development, rock type, and hydrological data. Temporal satellite image analysis confirmed continued enlargement of the affected zone and identified significant reactivation events during the monsoon periods of 2021 and 2022. The findings reveal that the Kotrupi landslide is progressively expanding, particularly toward the right flank, with widening observed in the crown area. The reactivation and expansion is primarily controlled by unfavorable rock orientation, presence of thrust (Main Boundary Thrust), tectonic activity; development of extensive joint planes, and tension cracks, all of which reduce the strength of the rock mass and soil during prolonged rainfall. The integrated methodology used in this study provides valuable insight into landslide reactivation mechanisms and helps identify areas susceptible to future slope failure. These findings can support hazard mitigation and risk reduction strategies for local communities and government agencies.