Bayesian estimation of surface strain rates in the peri-Adriatic, Balkans and Aegean region

The tectonics of the Eastern Mediterranean is governed by the convergence of the Eurasian, Nubian and Anatolian plates and characterized by the highest seismic hazard in Europe. Some boundaries between these plates are well defined and localized, such as the Hellenic subduction zone or the North Anatolian Fault (NAF). In contrast, the junction between Nubia and Eurasia near the northwestern end of the Hellenic subduction remains poorly documented, while the transition zone between the western end of the NAF and the normal faults in the Gulf of Corinth is characterized by distributed deformation.

Over the last decades, GNSS measurements have revealed that the Adriatic promontory moves slightly differently from the Nubian plate. This motion is well described by two rigid blocks, Adria and Apulia, which act as indenters pushing into the Alps and the Dinarides towards the north-east. Historically, the Balkan region has been considered a stable part of the Eurasian plate, experiencing negligible strain. However, recent GNSS data show that the entire peninsula undergoes significant deformation resulting in a clockwise rotation towards the Aegean domain, extending as far as central Serbia. Such deformation is outlined by recent earthquakes in Croatia (Petrinja, 2020) and Albania (Durrës, 2019). The style, magnitude, and spatial extent of the distributed deformation across the Dinarides and Albanides remain poorly constrained due to sparse GNSS measurements and the low strain rates expected in these regions.

In this study, we invert for the strain rate tensor over Italy, the Balkans and continental Greece using (i) the combined GNSS velocity field by Pina-Valdes et al. 2021 that offers the best coverage to date and (ii) the Bstrain code published by Pagani et al. 2021 which employs a Bayesian transdimensional approach. Our analysis produces probabilistic continuous maps of the strain rate tensor invariants (e.g. the second invariant and dilatation), vorticity, and interpolated horizontal velocities. We assess these results through statistical indicators derived from their probability density functions (PDFs), and make them openly accessible via an online plateform https://bstrainplotter.univ-lyon1.fr, in agreement with the FAIR principles.

These findings enable a detailed tectonic and geodynamic analysis of the region, grounded in a refined knowledge of surface deformation. We delimit the various tectonic styles based on the strain rate tensor's principal directions and highlight key features through representative cross-sections. This provide insights, for example, on the along-strike segmentation of the strain rates along the Apennines, the continuous arc-shaped compressive limit to the north and east of the eastern Alps, and a marked zero divergence line continuous from the Albanides region to the Hellenic subduction zone.