APPLICATION OF GPS FOR STUDY THE GEODYNAMIC PROCESSES IN THE REGION OF SOUTHWESTERN BULGARIA

The article summarizes the main geodetic activities performed in the region of Southwestern Bulgaria to study the modern crustal movements and clarify the geodynamic situation of the region. The study area is bounded to the north of the southern slopes of the Balkan Mountains, to the south to the southern slopes of the Rila Mountains, to the west � the western border of Bulgaria and to the east � the beginning of the Upper Thracian plain. The area has a complex geological structure with many active faults that must be studied. The region is of particular interest due to its high population density and high concentration of industrial facilities and resources. The main geodetic method for studying the crustal movements are GPS measurements, their processing and analysis of the results. To study the modern crustal movements in 1996- 1997, a geodynamic network was built that cover Southwestern Bulgaria. The network is designed for precision GPS measurements, determination the velocities of points and calculation of active strain. The results for velocities and strain rates of longtime monitoring are given. The velocities of the points are between 1.5mm/y of the northern most station and slightly over 3mm in the southern most station. The obtained result for strain rate field shows dominating N-S extension and the deformation is not uniformly distributed over the area. The strain rate field result confirms that the movement of points in the region of southwestern Bulgaria is in a southerly direction relative to stable Eurasia. This extensive movement of southern Bulgaria and northern Greece is also confirmed. Due to the long period of measurements the results are highly reliable and can be used for detailed geodynamic and geological study of the active fault structures in the region.