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

Daniela Valigi (1), Lucia Mastrorillo (2), Costanza Cambi (1), Massimiliano Rinaldo Barchi (1), Carlo Cardellini (1), Roberto Checcucci (3), Lucio Di Matteo (1), Francesco Frondini (1), Francesco Mirabella (1), Stefano Viaroli (2) & Isotta Vispi (1)
(1) Dipartimento di Fisica e Geologia, Università degli Studi di Perugia Via A. Pascoli snc, 06123 Perugia, Italy. (2) Dipartimento di Scienze, Università degli Studi Roma Tre, Largo San Leonardo Murialdo 1, 00146 Roma, Italy. (3) Regione Umbria, Servizio Risorse Idriche e Rischio Idraulico, Piazza Partigiani 1, 06124 Perugia, Italy. Corresponding author e-mail: daniela.valigi@unipg.it

Variations of springs discharge due to seismic events are rather common. On 2016 October 30^th 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 the following 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.

Earthquake, Groundwater flow, Spring, Groundwater geochemical, Central Italy.