Displacement history and potential triggering factors of Baige landslides, China revealed by optical imagery time series

Abstract

In this study, on the basis of the image correlation technique and the time-series images of Landsat-8 (L8), Sentinel-2 (S2), and GaoFen-2 (GF2), a systematic technical process is designed to investigate the precursory displacement evolution of two successive slope failures occurred in Baige Village, China on Oct. 11, 2018 and Nov. 3, 2018. An innovative fusion strategy is proposed to investigate the displacement history of the Oct. 11, 2018 Baige landslide, which has two steps: (1) selecting the optimal correlation window size and search step to eliminate the inconsistency of image correlation for different sensors, and (2) inverting the fused displacement time-series from correlation results to enhance the temporal sampling density. The normalized displacement velocity indicates that the Oct. 11, 2018 Baige landslide is characterized by high-speed sliding (28 m/yr) and high shear outlet with an average elevation difference of around 82 m. The fused displacement time series indicates that the whole phase transformation can be from the secondary stage to the tertiary stage on Mar. 26, 2017. Furthermore, the displacement velocity shows four quiescence phases in the secondary stage and two acceleration phases in the tertiary stage. The seasonal precipitation is assumed as the main external triggering factor, and it combined with the brittle geological material attributes to control the precursory landslide displacement evolution and caused the catastrophic slope failure on Oct. 11, 2018. The precursory displacement signals with a magnitude above 5 m/day of the second landslide (Nov. 3, 2018) is quantified by the S2 image correlation. This study highlights the prospects of optical observation time series with medium-/high-resolution in detecting and quantifying the spatio-temporal evolution characteristics of long-term creeping landslides which may play a significant role in the early warning of the catastrophic slope failure.