Persistent Scatterer Interferometry (PSI) to detect surface deformation in the Larderello-Travale geothermal area (Tuscany, Italy)

The present study aims to verify applied PSInSAR techniques over Larderello and Travale/Radicondoli geothermal areas, where surface deformation has been already monitored using precise topographic levelling methods. In these area, located in southern Tuscany (Italy) about 15 km apart, two main interconnected reservoirs have been identified: a shallow reservoir hosted in sedimentary units (limestone and anhydrite) and a deeper reservoir hosted within metamorphic and intrusive rocks. We have analysed PS information, from radar satellites ERS (European Remote Sensing Satellite) for the period 1993-2000, and ENVISAT (Environmental Satellite) satellite acquired between 2003 and 2010. For ERS satellites, only descending geometry data set was available. Analysis of the data showed that, in the period 1993-2010, the Larderello and Travale/Radicondoli geothermal fields were subject to subsidence phenomena with maximum rates of deflection of about 15 mm/yr and 29 mm/yr, respectively.The zones of greater subsidence are localized in the central part of the geothermal fields, and show a good correlation with the areas of greatest exploitation. Unfortunately there are no satellite data covering periods prior than 1993; however, previous monitoring of ground vertical movements performed with precise topographic levelling (from 1973 to 2003), allow us to reconstruct the subsidence trends of the area and to make a comparison between the two different methodologies for the 1993-2003 time span. This study confirmed that mapping and monitoring land surface deformation can provide useful information on time evolution of geothermal system from exploration to exploitation. The analysis of spatial and temporal changes of these phenomena can be used to prevent and minimize envinromental and infrastructure impact.