Geodetic constraints on kinematics of southwestern Bulgaria from GPS and levelling data

Abstract

AbstractSouthwestern Bulgaria belongs to the southern marginal parts of the central Balkan neotectonic region and borders the northern side of the highly seismic north Aegean region. The recent horizontal and vertical motion of the tectonic structures is controlled primarily by the collision stage, caused by continuing ENE palaeosubduction in the Ionian and Adriatic seas and extensional processes northwards of the North Aegean Trough. The present-day generation of small to moderate seismicity and crustal faulting suggests that the complex tectonic processes in the SW Bulgaria region are active. To monitor and study the tectonic deformation in SW Bulgaria, a global positioning system (GPS) network was established in early 2001. Analysis of GPS data from 1996 to 2004 resulted in a horizontal velocity field representing active surface deformations. Horizontal velocities at 38 GPS sites with respect to stable Eurasia are obtained. A new map of the recent vertical velocities is compiled, based on recomputed data from the repeated precise levelling for the period 1929–1991. We obtained evidence of recent active faulting. Based on the geological and geodetic data the SW Bulgaria is separated into five blocks with homogeneous kinematic behaviour. The average motion of each block varies from 1.3 to 3.4 mm a−1, and the whole region velocity is c. 1.8±0.7 mm a−1 in a direction N154° with respect to stable Eurasia. Geodetic data correlate well with the geological data on neotectonic motions in SW Bulgaria.