The studied area belongs to the Sannio-Matese zone, one of the most active seismic regions of the southern Apennines, where destructive earthquakes have occurred several times in the past. At the present, the area is characterised by low-energy sequences (Mdmax= 4.1) but not much is known about the tectonic structures responsible for such seismicity (Vilardo et al., 2003). The Sannio-Matese area is located in the frontal portion of the Apennine fold and thrust belts, at the junction between the northern and southern subsidiary arcs. At this location different tectonic styles are superimposed as a result of Neogene and Quaternary thrust, strike-slip and extensional tectonics (Di Bucci, 1995; Corrado et al., 1997). Two geological units characterise the Sannio-Matese area:
1. the Molise Unit having highly variable structural trends, ranging from EW in the south to N-S in the north;
2. the Sannio Unit is interpreted as a rootless thrust sheet originally deposited in a deep basin area located internally alongside the Latium-Abruzzo carbonate platform (Patacca et al., 1992). According to unpublished surface and subsurface data (Corrado et al., 1998) the entire thickness of the Sannio Unit is estimated to be about 3500 m.
Carbonates in this area are intensely fractured and host very important aquifers. They are locally affected by huge CO2 and H2S fluxes that play a very important role in defining the degree of water-rock interaction and, consequently, the final water chemistry. These gases rise along well known local and regional faults that cross the area. Moreover, near the town of Telese, extensive outcropping travertine layers are found, testifying to past geochemical processes acting in the area. Moreover, the Telese area is characterised by the presence of an ancient spa / hot spring tradition. The sulphur spring formed after the 1349 earthquake causing the mineral water discharge.
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