Executive Summary : | Landslide, though a normal physical process of hillslope erosion, poses the socio-economic risk to human life and infrastructure in the mountain region (Kanungo and Sharma, 2014; Martha et al., 2015; Pradhan et al., 2019; Sundriyal et al., 2023). Despite the rising global landslide mortality risk, effective evaluation of disastrous influences of landslides has been infrequent (Sassa, 2015; Klimes et al. 2019). Such evaluation approaches could be regional or local. However, effectiveness in such approaches cannot be rationalized until both the landslide triggering factors; rainfall and earthquake are evaluated together & their effects are evaluated in relative context (Lin et al. 2006; Bontemps et al. 2020; Kumar et al., 2021). Despite the numerous case studies of rainfall induced slope failures in the earthquake affected terrain, studies predicting the potential effects of both factors have been relatively rare. Necessity of such studies becomes more critical in view of an annual average of more than 4,000 landslide related deaths worldwide in last decade (Froude and Petley, 2018). According to the International Disaster Database (EM-DAT), between 1990 and 2015, landslides occurred in Asian nations, mainly India and Nepal, accounting for about 54% of the total global incidence (Froude and Petley, 2018). Due to seismicity and extreme events linked to climate change, India, particularly the Himalayan range, is one of the regions with the highest risk of landslip casualties and deaths. The eastern Himalaya is relatively less researched in this context, despite the fact that the entire Himalayan range is prone to frequent seismicity and periodic rainfall due to collisional orogeny and numerous precipitation systems, respectively. Given the regular landslides in the Eastern Himalaya that cause significant loss of life and property, this issue has become critical. Further, though there have been some studies in this region exploring landslide perspectives (Luirei and Bhakuni, 2008; Singh et al., 2014; Das et al., 2021; Saha et al., 2023), no study has been performed to evaluate the relative influence of climate extremes and earthquakes on the hillslopes. Owing to the capability to represent the progressive deformation under various conditions, numerical modeling can be considered as a primary approach for effective evaluation of slope instability and associated risk. Though the continuum modelling based approaches have been common for the local scale evaluation, estimation of large strain, particularly during the seismic analysis requires discontinuum modeling (Jing 2003). Along with stability evaluation, prediction of potential run-out during the slope failure constitutes a principal risk evaluation approach. Apart from the stability and runout aspect, impact of regional hydro-climatic processes like flood is also required to explore because such processes generate many landslides in their route in the downstream regions (Xu et al., 2012). |