Abstract
Abstract. This study presents and discusses horizontal and vertical geodetic velocities for a low strain rate region of the south Alpine thrust front in northeastern Italy obtained by integrating GPS, interferometric synthetic aperture radar (InSAR) and leveling data. The area is characterized by the presence of subparallel, 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−1 of NW–SE shortening associated with the Adria–Eurasia plate convergence, but the horizontal GPS velocity gradient across the mountain front provides limited constraints on the geometry and slip rate of the several subparallel thrusts. In terms of vertical velocities, the three geodetic methods provide consistent results showing a positive velocity gradient, of ∼ 1.5 mm a−1, across the mountain front, which can hardly be explained solely by isostatic processes. We developed an 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 it 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 (locking depth equals 9.1 km and slip rate equals 2.1 mm a−1) 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 seismological and geomorphological evidence of active tectonics is often scarce or not conclusive.
Highlights
Diffuse deformation, slow tectonic rates and long repeat times of large earthquakes make the estimate of seismic hazards at continental plate boundaries a challenging task
The inversion results show that the Bassano– Valdobbiadene thrust is characterized by a greater locking depth (LD = 9.1 km) and a faster dip-slip rate (2.1 mm a−1) than the Montello ramp fault (LD = 5.6 km, SR = 0.5 mm a−1)
Our results are consistent with the conclusions of Barba et al (2013) who developed a two-dimensional finiteelement model constrained by the leveling vertical rates which shows that the amount of interseismic locking associated with the Bassano–Valdobbiadene thrust (BVT) must exceed that associated with the Montello thrust (MT)
Summary
Slow tectonic rates and long repeat times of large earthquakes make the estimate of seismic hazards at continental plate boundaries a challenging task. This is the case of the Italian Alps, a classic example of a broadly deforming continental collisional belt (Schmid et al, 2004). The present-day convergence between the Adriatic and Eurasian plates is largely accommodated in the eastern Southern Alps (ESA) (e.g., D’Agostino et al, 2005; Cheloni et al, 2014) where the Adriatic lithosphere underthrusts the Alpine mountain belt. For the Venetian sector of the ESA (between the Schio–Vicenza line and the Cansiglio plateau; see Fig. 1), historical and instrumental earthquake records in-
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