ИСТИНА

The Black Sea coast of the Great Caucasus has always been a region of high landslide risk due to widely spread clays and marls seasonally saturated by abundant rainfalls. In recent years landslide risk assessment has become vital because of strongly increased human-induced impact dealt with construction of the Sochi-2014 Olympic Games facilities. We studied the landslide activity in the area of the Bolshoy Sochi (Big Sochi) using the StaMPS PS-InSAR and SBAS methods. We incorporated all available radar images from the satellites with different wavelengths: 17 ALOS images (track 588A, ascending orbit, 22.01.2007-17.09.2010), 13 Envisat images (track 35D, descending orbit, 29.11.2010-23.03.2012), 17 TerraSAR-X images (track 54A, ascending orbit, 24.12.2011-13.09.2012). For all of these three sets of images we identified persistent scatterers (PS) with a density of more than 350 PS/km even for rural areas. For these PS’s we calculated surface displacements in the line of site (LOS) direction. Areas of relatively high surface displacement rates located using the SAR data appeared to match in many instances zones of high landslide activity identified by geological field observations. We present time series for the most active landslide areas of the Big Sochi. The calculated average surface LOS displacement rates vary from 15-20 mm/year up to 60 mm/year. For some places with extreme values of LOS displacement rates the values of displacement rates in the down - slope direction were also estimated. Analysis of the time series made it possible to determine periods of activity and relative stability of the landslides and compare them with ground observations. For example, high landslide activity in spring of 2012 initiated by heavy rainfalls can be clearly seen in the time series. Activity of the landslides in the beginning of 2012 is most pronounced in the results of PS-InSAR processing of the TerraSAR-X data. Detailed analysis of the time series is performed for the Baranovka landslide where very strong movements during 23-24 January 2012 damaged 35 houses. Large displacements resulted in temporal decorrelation between the SAR image from 24.12.2011 and the later images. Reliable estimation of displacement rate appeared to be possible only since 17.02.2012. There have been revealed the period of relatively high landslide activity (17.02.2012 - 10.03.2012) when the LOS displacement rates reached 30 mm/month (about 120 mm/month down the slope). Then displacement rates decreased gradually and since June 6, 2012 have not exceed 2-3 mm/month (10 мм/month down the slope), indicating that the landslide has become more stable. Displacement fields for the Baranovka landslide for the period of large displacements were also estimated using pairs of interferograms. These estimates are in good agreement with time series obtained for the corresponding PS’s. Results obtained with the StaMPS software are compared to some of those using the DePSI and GiANT (SBAS, NSBAS) methods. DePSI produces nearly the same values of displacement rates as StaMPS for the Mamaika landslide. SBAS makes it possible to locate the area of relatively strong movements on the Mamaika landslide but calculated values of displacement rates are lower than using StaMPS. All this illustrates high efficiency of SAR Interferometry in monitoring of landslide activity in the area of the Black Sea coast of the Caucasus where landslides are numerous.