Surface displacements of the Heifangtai terrace in Northwest China measured by X and C-band InSAR observations

Abstract The Heifangtai terrace located in Yongjing County of Gansu Province in northwest China is characterized by a large number of landslides with frequent failure events related to agricultural irrigation activities. Thus, it is a task of great importance to identify and monitor the active loess slopes and sort out the impact factors. In this study, we employed the time series InSAR method to map the active slopes in the Heifangtai terrace with two TerraSAR-X data stacks covering the year of 2016 and two Sentinel-1 data stacks from 2016 to 2018. The detected active spots are mainly distributed along the edges of the terrace. Time series displacements derived from TerraSAR-X and Sentinel-1 observations were validated by comparisons against GPS and crack gauge measurements. Good agreement between InSAR and GPS was achieved at slow moving locations, while unwrapping errors induced by sudden accelerations make InSAR underestimate the pre-failure displacements with respect to GPS measurements. The trends of InSAR-measured displacement and crack gauge measurements also match well with correlation higher than 0.75. InSAR-measured displacements at the Jiaojia landslide group were highly correlated with the bury of groundwater record, which suggested that the rising of groundwater level may seriously decrease the stability of loess slopes.