Hydrogeochemical response of karstic aquifers to strong earthquakes: The 2016-2017 Amatrice-Norcia sequence in central Italy
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The Alburni Massif represents one of the most important karst regions of the Southern Apennines, and it has a high potential as a water resource. This paper reports a hydrogeochemical evaluation of sampled waters from the southern sector of the Alburni Massif (Campania region, Italy). Five water samples were analysed (three from natural springs and two from wells) to i) evaluate the hydrogeochemical properties of the waters in the study area and ii) understand the groundwater flow in this system. Waters sampled were classified as Ca-HCO3 due to enrichment from different alkaline elements (Ara+ + k+) and carbonate (HCO3- + CO32). This classification is in agreement with the lithologies present in this area. Groundwater flow was connected to the fault line passing through the south-west sector of the complex, which divides the Massff into two large structures situated to the east and the west.
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Abstract Using artificial tracer tests, this study confirms the presence of a single basal aquifer feeding the springs in the wide and complex hydrogeological boundary of the Sibillini Mountains of central Italy. The tracer was introduced into the sinkhole of the Castelluccio di Norcia plain. The tracer test results, observed at the studied springs, highlight the changes induced by the 2016/2017 earthquake in the water circulation of the aquifer system. In particular, the seismic events increased the hydraulic conductivity of the basal aquifer, with a consequent increase in the springs’ flow rates at the western hydrogeological boundary and a decrease in the flow rates at the eastern Adriatic hydrogeological boundary. This phenomenon is in accordance with the hydro-structural framework of the area. The study also investigated the relation between groundwater circulation and tracer behaviour in the springs during the pre- and post-earthquake periods. The tracer test results led to the formulation of hypotheses about water circulation of the area. The trend of the tracer breakthrough curves demonstrates that the upper portion of the basal aquifer is characterised by fast water circulation similar to that in the epiphreatic area of karst aquifers, while a slow circulation due to fissures with interconnected drains occurs in the deepest portion of the aquifers. The obtained results highlight how tectonics and karst can affect the hydrogeological setting of the Apennine carbonate chain; in particular, the seismicity of central Italy may alter groundwater circulation for a long period of time when great magnitude earthquakes occur.
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