We apply a blind source separation algorithm to the ground displacement time series recorded at continuous Global Positioning System (GPS) stations in the European Eastern Alps and Northern Dinarides. As a result, we characterize the temporal and spatial features of several deformation signals. Seasonal displacements are well described by loading effects caused by Earth surface mass redistributions. More interestingly, we highlight a horizontal, nonseasonal, transient deformation signal, with spatially variable amplitudes and directions. The stations affected by this signal reverse the sense of movement with time, implying a sequence of dilatational and compressional deformation that is oriented normal to rock fractures in karst areas. The temporal evolution of this deformation signal is correlated with the history of cumulated precipitations at monthly time scales. This transient horizontal deformation can be explained by pressure changes associated with variable water levels within vertical fractures in the vadose zones of karst systems. The water level changes required to open or close these fractures are consistent with the fluctuations of precipitation and with the dynamics of karst systems.

Changes in continental water storage generate vertical surface deformation, induce crustal stress perturbations, and modulate seismicity rates. However, the degree to which regional changes in terrestrial water content influence crustal stresses and the occurrence of earthquakes remains an open problem. We show how changes in groundwater storage, computed for a ∼1,000 km² basin, focus deformation in a narrow zone, causing large horizontal, nonseasonal displacements. We present results from a karstic mountain range located at the edge of the Adria‐Eurasia plate boundary system in Northern Italy, where shortening is accommodated across an active fold‐and‐thrust belt. The presence of geological structures with high permeabilities and of deeply rooted hydrologically active fractures focus groundwater fluxes and pressure changes, generating transient surface horizontal displacements up to 5 mm and perturbations of crustal stress up to 25 kPa at seismogenic depths. The background seismicity rates appear correlated, without evident temporal delay, with groundwater storage changes in the hydrological basin. With no evidence of pore pressure propagation from the hydrologically active fractures, seismicity modulation is likely affected by direct stress changes on faults planes.

The 2016–2017 Central Italy earthquake sequence struck the central Apennines between August 2016 and October 2016 with Mw ∈ [5.9; 6.5], plus four earthquakes occurring in January 2017 with Mw ∈ [5.0; 5.5]. We study Global Positioning System time series including near‐ and far‐field domains. We use a variational Bayesian independent component analysis technique to separate the post‐seismic deformation from signals caused by variation of the water content in aquifers at hundreds of meters of depth and of the soil moisture. For each independent component, realistic uncertainties and a plausible physical explanation are provided. We focus on the study of afterslip on the main structures surrounding the mainshock, highlighting the role played by faults that were not activated during the co‐seismic phase in accommodating the post‐seismic deformation. We report aseismic deformation occurring on the Paganica fault, which hosted the Mw 6.1 2009 L'Aquila earthquake, suggesting that static stress transfer and aseismic slip influence the recurrence time of nearby (∼50 km further south of the mainshocks) segments. A ∼2–3 km thick subhorizontal shear‐zone, clearly illuminated by seismicity, which bounds at depth the west‐dipping normal faults where the mainshocks nucleated, also shows aseismic slip. Since afterslip alone underestimates the displacement in the far‐field domain, we consider the possibility that the shear zone marks the brittle‐ductile transition, assuming the viscoelastic relaxation of the lower crust as a mechanism contributing to the post‐seismic displacement. Our results suggest that multiple deformation processes are active in the first 2 years after the mainshocks.

We study the time series of vertical ground displacements from continuous global navigation satellite system (GNSS) stations located in the European Alps. Our goal is to improve the accuracy and precision of vertical ground velocities and spatial gradients across an actively deforming orogen, investigating the spatial and temporal features of the displacements caused by non-tectonic geophysical processes. We apply a multivariate statistics-based blind source separation algorithm to both GNSS displacement time series and ground displacements modeled from atmospheric and hydrological loading, as obtained from global reanalysis models. This allows us to show that the retrieved geodetic vertical deformation signals are influenced by environment-related processes and to identify their spatial patterns. Atmospheric loading is the most important process, reaching amplitudes larger than 2 cm, but hydrological loading is also important, with amplitudes of about 1 cm, causing the peculiar spatial features of GNSS ground displacements: while the displacements caused by atmospheric and hydrological loading are apparently spatially uniform, our statistical analysis shows the presence of N–S and E–W displacement gradients. We filter out signals associated with non-tectonic deformation from the GNSS time series to study their impact on both the estimated noise and linear rates in the vertical direction. Taking into account the long time span of the time series considered in this work, while the impact of filtering on rates appears rather limited, the uncertainties estimated from filtered time series assuming a power law plus white noise model are significantly reduced, with an important increase in white noise contributions to the total noise budget. Finally, we present the filtered velocity field and show how vertical ground velocity spatial gradients are positively correlated with topographic features of the Alps.

Fluctuations in groundwater content may produce surface deformation and affect the elastic properties of the Earth’s crust. In this study, we evaluate the temporal variations of the Earth’s crust elastic properties (in the form of relative seismic‐velocity variations) in a tectonically active region in Northern Italy characterized by the presence of karst systems. In this area, GPS measurements already revealed hydrologically‐induced deformation, modulated by changes in groundwater storage. We study the relation of our seismological observations with the geodetic and hydrological results and identify the effects of groundwater‐content variations in the seismic‐velocity perturbations. Our results show that hydrologically‐induced changes in karstic media produce significant seismic‐velocity perturbations, therefore its role in tectonic‐stress adjustment studies must not be ignored. Depth sensitivity analysis of our results constrain the crustal perturbations to range between 500 and 3,500 m depth. Results from scattering imaging locate the crustal perturbations along the main local karst systems.

We study vertical ground displacement time series from Global Navigation Satellite System (GNSS) stations to measure deformation associated with hydrological drought in the Po river basin. Focusing on interannual trend changes, rather than seasonal (annual) components, we found a clear spatially correlated deformation signal that is temporally (anti)correlated with changes in the Po river level and the SPEI‐12 drought index, with stations moving upward during periods of river/index level decrease and vice versa. In the 2021–2022 time span, which culminated in the most severe drought of the last two centuries, we estimate the amount and spatial distribution of water loss in the basin and its surroundings. Excluding the seasonal signals, between January 2021 and August 2022, the GNSS stations underwent uplift, up to 7 mm, which corresponds to ∼7 Gtons of water loss. Compared to Global Land Data Assimilation System and Gravity Recovery and Climate Experiment estimates, GNSS results show a similar temporal evolution of water content but a more heterogeneous distribution of values. We show that continuous GNSS networks provide an effective way to monitor multiannual trend changes in water storage even in small water basins and serve as a reliable indicator of drought severity.