Mass-wasting effects induced by the 2015 Gorkha (Nepal) Mw 7.8 earthquake within a large paleo-landslide site adjacent to the Tatopani Border Station, Nepal: implications for future development along the critical Bhote Koshi River valley transport corridor between Nepal and China

The 2015 M-w 7.8 Gorkha earthquake and its aftershocks caused nearly 9000 deaths and more than 23,000 injuries and triggered thousands of landslides and other mass-wasting effects in the steep, rugged topography of Nepal. In this paper, new slope failures and tension cracks induced by the 2015 Nepal earthquake are documented in steep terrain west of the Tatopani Border Station, which lies along the deeply incised Bhote Koshi River valley, a critical trans-Himalayan transport route between south Asia and Tibet/China. The affected area west of the Tatopani station is the site of a large reactivated paleo-landslide that has experienced repeated failures. The Tatopani station is downslope from the amphitheater-like landslide scar and is constructed on distal landslide debris in a position vulnerable to future landslide and fluvial erosion hazards. We carried out detailed field investigations to document different types of geohazards around the station and present an evolutionary model for past and present landslide development. In addition, a simple numerical model was constructed to evaluate the stability of the large paleo-landslide body under different earthquake conditions. Simulated results suggest that the paleo-landslide body is stable without seismic loading. However, the large paleo-landslide will be remobilized again by large slope failures if the PGA of future earthquake exceeds 0.35 g. We suggest that the results presented in this paper should be taken into consideration during earthquake-resistant design of the border station and other infrastructural development along the Bhote Koshi Valley.