Persistent Deformation in a Post-Collisional Stable Continental Region: Insights from 20 Years of cGPS in Romania

Abstract. The Carpathian Region, located at the edge of the East European Platform, presents a unique tectonic setting where major deformation associated with subduction and collision appears to have ceased around 8 million years ago. Yet vertical movements and present day seismicity continued afterwards, suggesting ongoing crustal deformation and challenging our understanding of intraplate earthquakes and the processes driving these phenomena in an area considered as a stable continental interior. In this study, we analyse over two decades of continuous GPS (cGPS) data from 143 permanent stations to estimate both horizontal and vertical crustal motions, constructing the most accurate model of crustal deformation in the region to date. The estimated velocity field indicates a southward drift of the South Carpathians and Moesia relative to Eurasia, with velocities ranging from 0.5 to 2 mm/yr. We detect a more complex pattern of vertical uplift and subsidence in the foredeep, challenging a previously held view that this region is solely subsiding. This pattern may reflect localized uplift in response to processes such as the Vrancea slab break-off beneath the South-East Carpathians. Crustal scale active faults accommodate the observed differential motion, fragmenting the foreland. Furthermore, using a regularized horizontal velocity vector field, we estimate strain rate variations, maximum shear strain, and dilatation patterns across Romania, which closely align with observed crustal earthquake mechanisms. This agreement validates our results and indicates a significant influence of surface plate kinematics on the observed seismicity, in addition to the deep Vrancea slab dynamics. Our findings provide fundamental insights into the causes of crustal deformation at the transition between active collision zones and stable continental platforms, enhancing our understanding of intraplate seismicity in regions traditionally considered tectonically stable.