Probabilistic assessment of seismically triggered landslide hazard for Uttarakhand (India) in the Western Himalayas

Landslides are a major cause of earthquake damage, and the ability to anticipate seismically triggered landslide displacement is critical for seismic hazard assessment. The necessity for efficient measures for preventing and minimizing the damage caused by co-seismic landslides has prompted the development of innovative approaches for assessing areas exposed to seismically induced landslides at a regional scale. Uttarakhand is highly seismically active, and major geological formations of this region are heavily jointed or fractured. Landslides are common in this area, and the risk of earthquake-induced landslides is particularly significant due to the region's strong seismicity. The present study incorporated a combination of a probabilistic approach and modified Newmark’s method to obtain seismically induced landslide susceptibility maps. Firstly, a well-established probabilistic seismic hazard assessment method was utilized to calculate the probability of occurrence for various levels of earthquake shaking in terms of Arias intensity for different time intervals. Then by using an empirical equation based on Newmark’s displacement model, the slope strength demand was evaluated. The resulting slope strength demand values represent the minimal value of resistance required by a slope to maintain the probability of triggering an earthquake-induced landslide below a predetermined threshold. Finally, the spatial distribution of slope strength demand was compared with in-situ critical acceleration values computed using a modified Newmark method to determine slope failure probability. The obtained map presents a detailed demarcation of areas that will be affected by co-seismic landslide hazards in the future.