Geohazards Analysis of the Litang–Batang Section of Sichuan–Tibet Railway Using SAR Interferometry

The Sichuan–Tibet Railway (STR), as the second railway connecting the Tibet Autonomous Region with the rest of China, is recognized as a historical challenging project. There are widely distributed geohazards (e.g., landslides, sand-sliding slopes, collapses, ice avalanches, and debris flows) along the STR due to the significantly undulating terrains, unfavorable geological conditions, and intense tectonic movements. Therefore, it is necessary to identify the potential threats for the construction and regular operation of the STR. Interferometric synthetic aperture radar (InSAR) is a well-known tool for wide area geohazards detection with high precision. In this study, we employed small baseline subset analysis method to retrieve the ground displacement of the Litang–Batang section of the STR with C-band Sentinel-1 SAR images acquired from December 2015 to October 2019. The identified geohazards in this section are landslides, sand-sliding slopes, and seasonal frozen soils. High risk of geohazards is identified in the Maoyaba-Batang section through a hotspot and cluster analysis method. The head area of the ancient earthquake triggered Luanshibao landslide is identified active with displacement rate of −15 mm/yr, which might bring threat to the Sichuan–Tibet highway. Seasonal displacement due to freeze-thawing cycles of the seasonal frozen soils is detected in the alluvial area of the Litang River with maximum amplitude of 20 mm. Seasonal accelerations correlated with concentrated rainfall are identified on active slopes. Our study proved InSAR is an effective tool in detecting and monitoring mountainous unstable slopes.