Monitoring Landslide Activity in the Greater Sochi Region Using InSAR for the Period 2015–2024

The high landslide hazard in the intensively developed coastal areas of the Greater Sochi necessitates constant monitoring of landslide activity of slopes. This work is a continuation of research on the application of the satellite radar interferometry method (InSAR) to study landslide processes in this region. The paper presents an updated interactive map of surface deformations for the Central and Adler Districts of Greater Sochi based on interferometric processing of radar images from the Sentinel-1A satellite from ascending and descending tracks for the period 2015–2024. The latest update of the map is available on the Internet at https://adler.nextgis.com/resource/1214/display?panel=info . The images were processed using the SBAS (Small Baseline Subset) ENVI SARscape software. Derived from the results of the interferometric processing, the average values of displacement rates in the line of sight direction (Vlos) and down the slope (Vsd) are presented on the map as layers for two periods: 2015–2021 and 2021–2024. For both periods, active deformations areas (ADAs) where Vlos exceeds the specified threshold of 10 mm/year are highlighted on the map. For 2015–2021, 58 most significant ADAs are identified. For 2021–2024, 27 newly appeared ADAs are recorded, and 15 ADAs of the 58 identified for the previous period show an increase in activity. The possibility to use InSAR to monitor landslide activity in this region is shown by a case study of a landslide slope in the vicinity of the Gornaya Olimpiya 2 cottage settlement built in 2020. Comparison of the results presented on the map for 2015–2021 and 2021–2024 shows an increase in the size of the ADA area over time, according to data from the ascending track 43A, while according to data from the descending track 123D, there is also an increase in absolute displacement rates: Vlos changes from –10…–30 to –30…–50 mm/year. Joint analysis of the time series of displacements at various locations in the settlement and immediate vicinity of its borders, together with precipitation graphs shows that heavy autumn–winter precipitation in 2021–2022 initiated activation of the landslide in this area in February 2022. Maximum displacement rates up to 25 mm/month are recorded at the southern border of the settlement. This dangerous situation requires continuous monitoring.