InSAR observations from multiple tracks reveal rainfall modulation of post-failure reactivation of the Xiongwadashan landslide

Large mountain landslides may remain active after major movement, yet the migration of dominant deformation zones, internal post-failure partitioning, and rainfall modulation remain insufficiently understood. We investigate the Xiongwadashan (XW) landslide on the northeastern Tibetan Plateau using Sentinel-1 LOS observations from selected pre- and post-event periods between 2017 and 2025, terrain-constrained three-dimensional displacement estimates for 2022–2024, CHIRPS rainfall data, and field observations. Before the September 2018 event, deformation was concentrated mainly in the middle–lower slope. After failure, the dominant deformation zone shifted to the middle–upper slope and later extended partially downslope toward the middle slope. Movement was dominated by horizontal, near-downslope displacement, with a peak cumulative east–west displacement of ~ 210 mm at XW1-3. Integrated LOS deformation, three-dimensional displacement, time series, and geomorphic evidence delineated high-deformation, transitional, and low-deformation kinematic zones. The high-deformation zone showed stronger displacement increases following concentrated rainfall, while deformation persisted during relatively low-rainfall periods. These results indicate that rainfall mainly modulated stage-wise acceleration rather than controlling long-term activity, and demonstrate the value of integrating temporal deformation-zone migration with internal kinematic zonation for post-failure landslide monitoring.