Study of Surface Deformations Induced by Underground Mining and Neotectonic Activity
AGH University of Science and Technology, POLAND
The application of Permanent Scatterer InSAR technique (PSInSAR) to characterize dynamical surface processes in the mining and post mining areas in Upper Silesian Basin in Southern Poland will be presented. Among the processes that were recognized to be the most harmful in this area are deformations of ground surface, changes of hydrogeological conditions and geochemical transformations of soils. The subsidence phenomenon was recognized to be the most important and core reason of the deterioration and devastation transformations of ground surface in the presented mining area. Another mining-induced and subsidence related phenomenon is the seismicity. It has been continuously triggered in the southern Poland mining areas. Every year hundreds of thousands of seismic events are detected. Most of them have small energy and do not affect the surface. On the other hand there are events that can significantly influence the surface because of magnitudes 4.0 or even higher (the largest induced events had magnitude equal to 4.6). These strong events increase the destructive environmental impact of coal mining especially on highly urbanized areas. The important feature of Upper Silesian Basin is a dense fault system with throws which vary from several meters to over three hundred meters. The main dislocations in discussed region are oriented in W-E or NW-SE direction. The main faults are crossed by smaller faults with different orientation. The detected neotectonic movements if some faults coincide with subsidence induced by underground mining. In our study only the subsidence analysis of large faults with throws over fifty meters was presented . Because of the character of typical Polish mining areas the PSInSAR data analysis and interpretation appropriate to densely inhabited, agricultural and forested areas was chosen. The PSInSAR data used in this work were obtained by processing 79 SAR images acquired form ERS-2 and ENVISAT satellites. In the first part of this work, analysis of ground deformations values was done. It was performed separately for downthrown blocks and upthrown blocks of the main faults and then compared with mining activity and underground mining activity. The one-way variance analysis was done to examine the statistical significance of the difference between average velocities of subsidence in downthrown and upthrown blocks. In the second part of work an analysis of spatial dependence between fault location, velocity of deformations and seismic activity was performed. For these data the directional semivariograms were calculated in downthrown and upthrown blocks of the faults. Results of analysis show that main faults divides area of study into regions with significant difference of average values of ground deformations. It has been found that the downthrown and upthrown blocks of the main faults have different spatial variations of ground deformations. Performed analysis shows also that there is no linear correlation between values of ground displacements and the distance to lines of faults.