GNGTS 2018 - 37° Convegno Nazionale

210 GNGTS 2018 S essione 1.2 showing that for some segments of the Adria-Eurasia boundary aseismic deformation is likely. Moreover, Devoti et al. (2015) found that the same area, and in particular the Cansiglio plateau, is affected by deformation processes associated with the hydrological cycle in karsts. Serpelloni et al. (2018) studied GPS displacement time-series in an area encompassing the Veneto-Friuli Eastern Southern Alps and the Northern Dinarides by using the Variational Bayesian Independent Component Analysis (vbICA) (Gualandi et al. , 2016), a multivariate statistical analysis based on the solution of blind source separation problems. This method allows separating statistically independent signals, named independent components (ICs), characterized by different spatial and temporal features affecting GPS time series. The results of this analysis highlight two annual components (IC1 and IC3), interpreted as horizontal and vertical displacements associated with continental-scale surface hydrological loading, and a time-variable, non-cyclic signal (IC2). The horizontal displacements associated to this component are larger than the vertical ones, which are almost always below the noise level. Furthermore, the largest amplitudes are recorded in three karst areas of the study region, which are the Lessini Mountains, Val Belluna-Montello-Cansiglio and Northern Dinarides. The GPS stations respond to this signal by moving in opposite directions, reversing the sense of movement in time, implying a succession of extensional/compressional strains (Fig. 1), with variable amplitudes through time, oriented normal to rock fractures. The temporal evolution of IC2 is correlated with the history of cumulated precipitations at monthly time scales, and it can be explained by pressure changes associated with variable water levels within vertical fractures in the vadose zones of karst systems, as found for the Southern Apennines by Silverii et al. (2016). In this work, we tried to constrain the physical process causing this signal, testing if it is associated with water flow and changes in water storage in karst systems and linking it to the geological features of the area. Quantifying water storage variations cannot be done by using GRACE measurements, because of their limited spatial resolution at the Earth’s surface (200x200 km grids); we then decided to represent dynamic of hydrological basins, i.e. areas drained by a river, by means of rainfall-runoff models. These models describe how the rainfall over a basin turns into river flow once given as input rainfall and potential evapotranspiration. Among the outputs of such models, the temporal evolution of the amount of water stored within the basin (water storage variations) is exactly our target. We focused on the Val Belluna (i.e. Piave river basin) and the pedemountain front of the Venetian Southern Alps, because of the availability of both dense geodetic and hydrological data. In particular, we considered the hydrological basins defined by the Cordevole River at Ponte Mas and by Piave River at Belluno and Segusino (Fig. 2). The hydrological model that best reproduces the observed river flows is called GR5J, which is slightly differs from GR4J (modèle du Génie Rural à 4 paramétres Journalier), described in Perrin et al. (2003). We compared the time evolution of the model total water storage with the temporal evolution of IC2. The correlation between these two quantities is high (Fig. 2): 0.89/0.91 when considering the Piave basin at Belluno/Segusino and 0.78 considering the Cordevole basin at Ponte Mas. We built a bi-dimensional numerical model with the goal of understanding how water level variations in karst aquifers, rock fractures or fault zones can generate the displacements shown in Fig. 1. In order to take into account the topography and the geological features of Val Belluna and M.te Grapp a-M.te Cesen mountain chain, we implemented in the numerical model a geological profile of the Foglio Belluno of the Carta Geologica d’Italia (Fig. 3). We tested different sources of deformation in order to find the one that best reproduces the displacements obtained from the geodetic analysis, finding that it is the backthrust of theBassano-Valdobbiadene thrust fault. Since M.te Grapp a-M.te Cesen mountain chain is karstified and corresponds to an anticline, the top of it is characterized by a distension regime that generates sub-vertical fractures. We made the hypothesis that the meteoric water penetrates through the fractures and flow along an impermeable formation, converging to a sub-vertical fracture, the backthrust of