Major active faults of SW Bulgaria: implications of their geometry, kinematics and the regional active stress regime

Abstract: Southwest Bulgaria is an intracontinental region between the Dinaro-Hellenic and Balkan mountain ranges that has experienced infrequent, but strong and destructive earthquakes. The general geometric and kinematic characteristics of the major faults, mainly the active ones, are investigated, as the seismic activity is insufficient to describe thoroughly the active crustal deformation associated with the faulting. The results suggest a m jor rupture zone with a length of more than 50 km. The east-west-striking Kochani-Kroupnik-Bansko 'rupture zone ' was potentially associated with the large 1904 Kroupnik earthquakes, and has been found to transect the region joining the Kochani, Kroupnik and Bansko faults. In addition, a long-term slip rate ranging from 0.14 to 0.7 mm a-1 has been estimated for some large faults in the region using morphotectonic features. The most active faults are normal ones striking WNW-ESE to ENE-WSW, whereas the NNW-SSE- to NW-SE-striking faults tended to act as barriers to the growth of the former faults, as they do not exhibit much indication of recent reactivation. The stress regime d termined is extensional with the least principal stress axis (cy3) subhorizontal and oriented north-south. The fact that the active faults how geometric and kinematic characteristics, a well as estimated long-ter