Overview and new data on the active tectonics of Bulgaria: towards a comprehensive seismotectonic map

This paper presents a discussion on some aspects of the active tectonics in Bulgaria based on available literature data as well as recent research mainly focused on the identification and characterization of active faults in selected key areas. In particular, through tectonic, GPS and remote sensing data, also coupling geological observations with seismological data, we present here 1) a comprehensive map of major active faults in Bulgaria, although still in progress, and 2) a detailed study of various active structures, in particular in the Sofia Graben, Struma valley and surrounding regions. Our research highlights the occurrence in south-west Bulgaria of several major active faults, the majority of which are normal faults accommodating a roughly N-S to NNE-SSW extension, in line with GPS data and analysis of the instrumental seismicity. The extensional stress field, with associated tectonic and seismic activity, is likely to be related to the northern extent of the Aegean extensional system and its recent evolution. In the Balkan mountains area the tectonic activity is somehow more complex, responding to the interplay of the northward propagation of the Aegean extension and the influence of a roughly E-W compression, which determines local shear zones.