**3. Geologic and tectonic features of the studied areas**

South-Eastern Sicily is located in a complex tectonic region being at the boundary between African and European plates (see inset map in Fig. 2a). Along this border, Mt. Etna, a basaltic volcano more than 3300 m high and with a diameter of about 40 km, resulting from the interaction of regional tectonics and local scale volcano-related processes (McGuire and Pullen, 1989), is sited. The island of Malta is placed in the Hyblean foreland, belonging to the African plate. Most of the formations here outcropping were deposited during the Oligocene and Miocene when the whole area was part of the Malta - Ragusa platform and, as such, attached to the African margin (Pedley *et al.*, 1978).

The whole study area is delineated by the crossing of lithosphere structures that give rise to the origin of Mt. Etna and by the presence of the Malta Hyblean fault system that runs down the Sicilian coast towards the Ionian sea (ME in the inset map of Fig. 2a). A series of horst and graben structures, NW-SE and NNW-SSE oriented, that are linked to the Malta-Hyblean escarpment, characterize indeed the tectonic setting of this area.

On Malta, the geo-structural pattern is dominated by two intersecting fault systems which alternate in tectonic activity. An older ENE-WSW trending fault, the Victoria Lines Fault (or Great Fault), traverses the islands and is crossed by a younger NW-SE trending fault, the Maghlaq Fault (Fig. 2b), parallel to the Malta trough which is the easternmost graben of the Pantelleria Rift system. The faults belonging to the older set, all vertical or sub vertical, are part of a horst and graben system of relatively small vertical displacement (Illies, 1981; Reuther et al. 1985).

As concerns Mt. Etna, its eastern flank is the more tectonically active part. Here, several NNW and NNE-trending fault segments (Timpe fault system, TFS), arranged in a 30 km long system (Fig. 2a), control the present topography and show steep escarpments with very sharp morphology (Monaco *et al*., 1997). This system represents the northernmost prolongation of the Malta Escarpment and forms a system of parallel step-faults having vertical offsets up to 200 m that down-throw towards the sea. Most of these faults are highly seismogenic and generate shallow earthquakes as well as co-seismic cracks in the soil and creep phenomena (Azzaro, 1999). In the north eastern part of the area, the active Pernicana fault system (PFS) represent the most significant tectonic structure. It is a strike-slip fault roughly E-W oriented with a length of about 18 km from the NE rift to the coastline (Neri *et al*., 2004; Azzaro *et al*., 2001; Acocella and Neri, 2005). At the end of this structure, close to the coast line, the Calata‐ biano and the Piedimonte faults (PF) can be considered, following Lentini *et al.* (2006), as the neotectonic structures of the basement outcropping in north-eastern Sicily (Fig. 2a).

The western flank of the volcano is affected by a moderate tectonic activity, the Ragalna fault system (RFS) being the main structure (Fig. 2a). This system is formed by three distinct fault segments the Calcerana and the Ragalna faults trending NE-SW and the N–S striking Masseria Cavaliere fault (Azzaro, 1999; Rust and Neri, 1996). This latter structure is a fresh east-facing escarpment up to 20 m high and 5 km long. Less evident compared to the previous one, the NE-SW striking Calcerana fault and the NE-SW trending structure, reported by some authors in the area between Ragalna and Biancavilla, do not show strong field manifestations.
