Kinematics, Seismotectonics and Seismic Potential of The Eastern Alps From GPS and Seismic Deformation Data

We discuss the kinematics and seismotectonics of the eastern Alps, at the boundary between Italy, Austria, Slovenia and Croatia, as obtained from the analysis of new geodetic and seismological data. The study area marks the boundary between the Adriatic microplate and the Eurasian plate, through a wide zone of distributed deformation, including a variety of tectonic styles within a complex network of crustal and lithospheric faults, inherited by the complex geodynamic evolution of the Alpine-Dinaric-Carpathian system. We use a dense GPS velocity field, obtained from the integration of continuous and survey-mode networks, a focal mechanisms catalogue and a seismic catalogue, with original and proxy moment magnitudes assessed from 1005 B.C., to estimate the tectonic deformation rates and develop an inter-seismic elastic kinematic model. Eurasian-fixed GPS velocities well describe the overall kinematics, with a transition from NNW-ward to NE-ward motion trends across Slovenia and Austria, but also show small but significant crustal deformation far from the major blocks boundaries, suggesting a complex configuration of interacting tectonic blocks in the study area. Geodetic deformation and seismic moment release rates are more localized, and characterized by larger earthquakes, along the southeastern Alps fold-and-thrust belt, which accommodates the large part of the ∼N-S Adria-Europe convergence, and in Slovenia, where a transition from ∼N-S shortening to the eastward escape of the Pannonian units occurs through a complex pattern of NW-SE oriented faults. We highlight strain accumulation off the main thrust fault segments, tens of km southward of the mountain front in the Venetian plain, in the southeastern Alps, in regions stroke by large (M>6.5) historical earthquakes (e.g. the 1117 “Verona” and the 1695 “Asolo” events). Our results, well constrained by a denser GPS velocity field, put new lights in the Italian southeastern Alps on i) the way the Adria-Eurasia convergence is partitioned across the southeast Alpine mountain range, ii) interseismic coupling along the main thrust faults and iii) the way N-S shortening is transferred, through right-lateral shear across the Dinaric system, to shortening across the Sava folds in Slovenia. We reveal forward interseismic slip in karst regions affected by hyhydrological induced deformation, corresponding to the low coupling segments of the southeastern Alps thrust system. A comparison of the estimated seismic moment release rates and the seismic moment accumulation rates, estimated from the model velocities, provide new insights into the seismic potential of the study region.