Abstract
On 17 June 2020, a large ancient landslide over the Aniangzhai (ANZ) slope, Danba County, Sichuan Province, China, was reactivated by a series of multiple phenomena, including debris flow triggered by heavy rainfall and flooding. In this study, Synthetic Aperture Radar (SAR) images acquired by the Sentinel-1A/B satellite and optical images captured by the PlanetScope satellites were jointly used to analyze and explore the deformation characteristics and the Spatial-Temporal evolution of the ANZ landslide before and after the multi-hazard chain. Several areas of pre-failure movements were found from the multi-temporal optical images analysis before the reactivation of the ANZ landslide. The large post-failure surface deformation over the ANZ slope was also retrieved by the optical pixel offset tracking (POT) technique. A major northwest movement with the maximum horizontal deformation of up to 14.4 m was found. A time-series InSAR technique was applied to analyze the descending and ascending Sentinel-1A/B datasets spanning from March 2018 to July 2020, showing that the maximum magnitudes of the Line of Sight (LoS) displacement velocities were −70 mm/year and 45 mm/year, respectively. The Spatial-Temporal evolution over the ANZ landslide was analyzed based on the time-series results. No obvious change in acceleration (precursory deformation) was detected before the multi-hazard chain, while clear accelerated deformation can be observed over the slope after the event. This suggested that heavy rainfall was the most significant triggering factor for the generation and reactivation of the ANZ landslide. Other preparatory factors, including the deformation behavior, the undercutting and erosion of the river and the outburst flood, the local terrain conditions, and earthquakes, might also have played an important role in the generation and reactivation of the landslide.
Highlights
To further the temporal evolution of the pre-failure whether therewhether were any precursory signals detected before the multi-hazard chain, a chain, a there were any precursory signals detected before the multi-hazard time-series analysis of selected measurement points was conducted
The deformation characteristics and Spatial-Temporal evolution of the ANZ landslide were investigated in detail by the joint use of multi-temporal optical images and time-series Interferometric Synthetic Aperture Radar (InSAR) analysis
The analysis of multi-temporal optical images clearly showed the spatial evolution of pre- and post-failure landslide features over the slope
Summary
The movement of a wide range of ground elements, such as rock masses, soil, debris, or garbage, is referred to as a landslide [1]. A series of geological, hydrometeorological, or even human-related factors, such as seismic and volcanic activity [2,3], climate change [4], heavy rainfall [5,6,7], subsurface and surface engineering work [8,9], deforestation [10], agricultural activities, and urbanization [11], have significantly contributed to the occurrence of landslides. The southwest part of China is prone to the occurrence of landslides because of the abundant precipitation and mountainous topography.
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