Hydrological crustal deformation in the Eastern Southern Alps

We applied a blind source separation algorithm to the ground displacements time-series obtained from the analysis of continuous GPS stations operating in the Eastern Southern Alps and northern Dinarides. This analysis highlighted both annual common mode component signals and a time-variable, non-cyclic signal characterized by a spatially variable response in the horizontal component. The first signal is well described by loading effects caused by Earth surface water mass redistributions, while the latter one has a temporal evolution that well correlates with the history of cumulated precipitations at monthly time scales and has larger amplitudes in karst areas of the study region. The GPS stations respond to this signal by moving in opposite direction, reversing the sense of movement in time, implying a succession of extensional/compressional strains, with variable amplitudes through time, oriented normal to rock fractures. We focus on the pedemountain front of the Venetian Southern Alps, and test the hypothesis that the succession of horizontal extensions and contractions recorded by the GPS stations are caused by the variation of the water level in hydrologically-connected fractures, whose temporal evolution is guided by water storage variation in the hydrological basin of this area. Having found high correlations between the temporal evolution of water storage variations, modeled by using rainfall-runoff hydrological models, and the deformation signal, we built a bi-dimensional numerical model based on finite-element method, containing the geologic feature of the study area, to understand how water storage variations generate the observed displacements. After testing different sources of deformation, we found that they are best reproduced by a sub-vertical structure corresponding to the backthrust of the Bassano-Valdobbiadene thrust fault. Here, the water accumulates because of the larger permeability of the fractured rock faults, varying its level up to tens of meter and then generating pressure changes that cause the observed displacements.