Interferometric study of landslides in urban Volga banks
Ludmila Zakharova(1) and Alexander Zakharov(1)
In spite of extremely high probability of dangerous landslides in Ulyanovsk (Volga region, Russia) there is no system of remote monitoring in the region. Interferometric observations give material illustrating landslide induced surface displacements. Estimation of the average annual velocity of the moving areas and their surface allocation by the methods of SAR interferometry can be used for prediction of the possible catastrophe. Comparison of the interferometry results and in situ observations allow validation of the measurements. Collecting information on the ground displacements before and after known landslides of the period 1992-1999 and comparison with interferometric results (22 ERS-1/2 archive scenes, ascending and descending orbits) is the essential part of the work.
The most important geological causes of the landslides in the region are montmorillonite which is one of the component of Volga banks, undercutting of the bank slopes by the river, and steep slopes. Therefore the most danger season is the spring with rains, snow melting and high water. Water makes montmorillonite swell, and this fact causes a deformation of geological layers. Water layers became stronger after rains, and they play a part of slickensides.
SAR Interferometry is the technique, which is sensitive to the terrain elevation, and Differential SAR Interferometry (DINSAR) allows estimating of surface motion in centimeters scale. Spring interferometric pairs of images are usually decorrelated because of snow melting, but summer and fall scenes show better temporal stability and are good for DINSAR processing. Pairs of images with short perpendicular baseline show displacements of the earth surface occurred in between the acquisition of two images.
Paper demonstrates the main results of the work: estimation of seasonal and annual dynamics of landslides activity
and detection of dangerous zones in Ulyanovsk city.