The launch of the medium resolution Synthetic Aperture Radar (SAR) Sentinel-1 constellation in 2014 has allowed public and private organizations to introduce SAR interferometry (InSAR) products as a valuable option in their monitoring systems. The massive stacks of displacement data resulting from the processing of large C-B and radar images can be used to highlight temporal and spatial deformation anomalies, and their detailed analysis and postprocessing to generate operative products for final users. In this work, the wide-area mapping capability of Sentinel-1 was used in synergy with the COSMO-SkyMed high resolution SAR data to characterize ground subsidence affecting the urban fabric of the city of Pistoia (Tuscany Region, central Italy). Line of sight velocities were decomposed on vertical and E–W components, observing slight horizontal movements towards the center of the subsidence area. Vertical displacements and damage field surveys allowed for the calculation of the probability of damage depending on the displacement velocity by means of fragility curves. Finally, these data were translated to damage probability and potential loss maps. These products are useful for urban planning and geohazard management, focusing on the identification of the most hazardous areas on which to concentrate efforts and resources.
Between 2008 and 2014, nine sinkholes occurred in northeastern Elba Island (Tuscany, Italy), an area with mostly flat terrain (called “Il Piano”) separating the municipalities of Rio nell’Elba and Rio Marina. The last sinkhole damaged the only road (SP26) between the harbour of Rio Marina and the northwestern part of the island. A bypass was immediately built, but the SP26 remains closed. Considering that sinkholes could be densely clustered in sinkhole prone areas, their detection and forecasting are key aspects of local administrative policies. In this paper, we present the results of an integrated geophysical survey aimed at (i) characterizing the geology of the area surrounding the SP26, and (ii) assessing the subsoil void hazard around the road system to support the decision to replace or restore the SP26. Therefore, for the purposes of this research, 120 singlestation seismic noise measurements were taken following the horizontal‐to‐vertical spectral ratio (H/V) or Nakamura technique, while eight 2D electrical resistivity tomography (ERT) and 17 3D‐ERT/induced polarisation measurements were also carried out in the study area. The H/V method allowed the estimation of the mean thickness of the alluvium, whereas the 2D/3D‐ERTs and IPTs permitted the characterisation of the electrical behaviours of the materials and the localisation of the lenticular sand and gravel bodies within a sandy silt layer. The large amount of collected data made the zonation of the subsoil void hazards possible.
The Tuscany region of Italy is widely affected by subsidence, landslides and floods, which severely impact buildings and infrastructure. In particular, Firenze-Prato-Pistoia basin has a long experience of ground deformation related to groundwater withdrawal. European remote-sensing satellite (ERS) data collected since 1992 have revealed the presence of several subsiding areas in the basin such as the south-eastern portion of the city of Pistoia. Sentinel-1 persistent scatterer interferometry (PSI) measurements for 2015–2018 confirmed the long-term subsidence of this area, associated with intense horticulture (plant nurseries). At the same time, Sentinel-1 data revealed the unexpected movement of Pistoia historic center, which has always been considered stable in the past. To identify the complex relationship between aquifer conditions and ground displacement, a hydrogeologic model of the Pistoia aquifers was developed, applying an integrated modelling procedure. Hydrodynamic-parameter distributions, calibrated and validated by means of Sentinel-1 PSI measurements, suggest that subsidence in Pistoia area is probably related with the combined impacts of groundwater extraction and highly compressible aquitards. To evaluate the potential evolution of ground displacement, numerical simulations were extended until 2050, using regional and global climate model data, analyzing three different pumping-rate scenarios. This led to the development of several subsidence hazard maps of the city of Pistoia that display the influence of groundwater extraction in controlling land subsidence in the area. This study emphasizes the importance of developing proper groundwater management policies, especially in alluvial aquifers made of fine compressible sediments, in order to sustainably utilize underground freshwater resources and to avoid related side effects.
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