Groundwater Monitoring in Regional Discharge Areas Selected as "Hydrosensitive" to Seismic Activity in Central Italy

The aim of this study was to identify potential patterns of hydrogeological and geochemical changes in response to seismic activity, including possible variations of ion concentrations, gas compositions, and isotopic ratios in groundwater. Different monitoring areas in Central Italy have been selected, located in regional discharge areas with abundant groundwater resources. They are located near active normal faults, along the southeast-ward prolongation of the faults that nucleated the L'Aquila 2009 Mw 6.3 event and more recently the seismic sequence of Amatrice-Norcia 2016-2017. The test-site selection has been based on both seismic and hydrogeological criteria. The areas are characterized by low strain rate, long frequencies of earthquake occurrence and high depth of the brittle-ductile transition, which are indicators of potential future earthquakes. In this framework, the hydrogeological setting is considered essential for obtaining reliable results applied to seismic purposes. Springs with long and deep flow paths in the regional aquifers are under monitoring. Indeed, the regional groundwater flows are also clearly influenced by deep fluids contribution. Consequently, the hydrogeological monitoring has been enhanced by continuous active radon and carbon dioxide probes, installed in some of the monitored springs. The results show significant inferences between hydrogeology and seismicity, having different characteristics in relationship with Amatrice-Norcia 2016-2017 seismic sequence and with global minor seismic activity. Based on these preliminary results, the second phase of this study is aimed to reinforce monitoring in selected springs and wells.