New insights into active tectonics and seismogenic potential of the Italian Southern Alps from vertical geodetic velocities

This study presents and discusses horizontal and vertical geodetic velocities for a low strain-rate region of the Southalpine thrust front in northeastern Italy obtained by integrating GPS, InSAR and leveling data. The area is characterized by the presence of sub-parallel, south verging thrusts, whose seismogenic potential is still poorly known. Horizontal GPS velocities show that this sector of the Eastern Southern Alps is undergoing ~ 1 mm/a of NW-SE shortening associated with the Adria-Eurasia plate convergence, but the horizontal GPS velocity gradient across the mountain front provide limited constraints on the geometry and slip-rate of the several sub-parallel thrusts. In terms of vertical velocities, the three geodetic methods provide consistent results showing a positive velocity gradient, of ~ 1.5 mm/a, across the mountain front, which can be hardly explained solely by isostatic processes. We developed a interseismic dislocation model, whose geometry is constrained by available subsurface geological reconstructions and instrumental seismicity. While a fraction of the measured uplift can be attributed to glacial and erosional isostatic processes, our results suggest that interseismic strain accumulation at the Montello and the Bassano-Valdobbiadene thrusts are significantly contributing to the measured uplift. The seismogenic potential of the Montello thrust turns out to be smaller than that of the Bassano-Valdobbiadene fault, whose estimated parameters (LD = 9.1 km and slip-rate = 2.1 mm/a) indicate a structure capable of potentially generating a Mw > 6.5 earthquake. These results demonstrate the importance of precise vertical ground velocity data for modeling interseismic strain accumulation in slowly deforming regions, where often seismological and geomorphological evidence of active tectonics is scarce or not conclusive.