Springs discharge variations induced by strong earthquakes: the Mw 6.5 Norcia event (Italy, October 30th 2016)

Abstract

Variations of springs discharge due to seismic events are rather common. On 2016 October 30th a Mw 6.5 earthquake occurred 5 km NNE of Norcia Town (Central Italy), at a depth of around 9 km b.g.l. The Torbidone spring, dry since 1979, was re-activated after the Norcia earthquake, and its discharge rose up to 1.6 m3/s in thefollowing weeks. The Torbidone, with other minor springs, feeds the baseflow of the Sordo River (Nera River basin), the discharge of which increased up to 2m3/s after the earthquake. The seismic events did not affect only the Torbidone spring but also the entire groundwater circulation of the Nera River hydrogeological basin.We analyzed the Torbidone spring area and its geological framework using hydrogeological, structural and geochemical methods, to evaluate the causes of the perturbations and the possible system evolution.The main factors thought to be responsible for the perturbations are the changes of permeability and the variations of hydraulic head. The mechanisms of these hydrogeological changes are currently being studied in order to define a conceptual model consistent with the observed response of Torbidone spring to the seismic event.