GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 1.3 165 tholeiitic and alkaline type of volcanism has developed inside the area. The two volcanic islands of Pantelleria and Linosa, and a large number of seamounts, many of which are poorly known (Fig. 1), testify to the volcanic activity. The main volcanic centres are aligned along N-S direction, from the Linosa Island to the Sicilian coast near Sciacca (Fig. 1). Historical eruptions were mainly underwater, of which there is only slight evidence for some of them (Calanchi et al. , 1989), and the volcanism is still active. The Pantelleria Rift forms the deepest part of the Straits and its floor consists of continental crust. The island of Pantelleria, with a NW–SE striking long axis of about 14 km and an orthogonal short axis of about 9 km, is the emerged portion of a volcanic structure, situated along the tectonic trench, which extends in a NW-SE direction for nearly 135 km. The recent eruption of the Foerstner volcano in 1891, along with the presence of thermal springs and fumaroles on the island, are evidence of a still active magmatic system at Pantelleria. Historical eruptions in the Sicily Channel. Except for the last 1891 Pantelleria and the 1831 Ferdinandea island eruptions, historical data report little evidence of previous eruptions in the Sicily Channel. We carried out an historical research on some volcanological and seismological compilations, as well as regional and Italian libraries, looking for first-hand sources (diaries, chronicles, official records, travellers’ reports, newspapers) and retrieving original documents written between 1600 and 1900. These documents have been critically analysed and interpreted to reconstruct the seismic and eruptive activity of the Sicily Channel. The first earliest information from historical accounts about eruptions in the Sicily Channel dates back to 1632 (Perrey, 1848). The volcanic activity was probably located in the Banco Graham, in the same area where the 1701 eruption (Fuchs, 1881) and the well-known 1831 eruption occurred. Aprobable submarine eruption took place in 1818 (Imbornone, 1817). Lastly, the 1845 and 1846 eruptions were also observed offshore (Perrey, 1846). On the other hand, the 1863 eruption reported by Fucks (1881) and then by Mercalli (1883) is a fake event. The eruptions of 1818 and 1831 where preceded, accompanied and followed by seismic swarms. Most of the shocks were strongly felt in Sciacca and in southwestern Sicilian coast. Regarding Pantelleria island, no eruption has occurred during the last 3000 years (Civetta et al. , 1984), while a shallow submarine eruption occurred in 1891, about 4 km NW from the Pantelleria coast. This event was preceded by vigorous seismicity (Baratta, 1892) and increasing fumarolic activity on the island. Significant uplift (up to 0.8 m) occurred at the NE coast of Pantelleria in May-June 1890 (0.55 m) and in 1891 (0.30 m) (Riccò, 1891) preceded by some shocks. The eruption began on October 17, emitting steam and throwing up large scoria (up to 1 m in diameter) to heights of 20 m. The activity culminated on the second day and then rapidly declined, ending completely on October 25. Sicily Channel seismicity. Although there are several studies on the ground deformation, gravimetry, petrography and structural geology of the island of Pantelleria (e.g. Mattia et al. , 2007, Catalano et al. , 2009, Lodolo et. al; 2012, and references therein), very little information about the seismic features of the Sicily Channel, and particularly Pantelleria island, is available. In western Sicily, the only destructive known earthquakes are related to the seismic sequence of 1968 (Belice valley). Historical data show that most of the earthquakes are located along the Sicilian southern coast. According to Rigano et al. (1998), the seismic activity close to Sciacca (south-western Sicily), manifested by low-energy sequences and lasting for several months (1652, 1724, 1727, 1817, 1831), is located offshore. Sciacca was often the only site where the earthquakes were felt and for this reason, the location of the events is problematic. Many of these swarms could be related with volcanic activity, even if there is only evidence for the 1831 and 1891 earthquakes (Marzolla, 1831; Gemellaro, 1831; Washington, 1909) and probably for the 1816-17 sequence. Moreover, the historical information, which was gathered along the coasts and islands of the Sicily Channel, may be biased if the actual seismogenic sources are offshore. In some cases, the seismic activity was concomitant with submarine volcanic activity