Regional tectonic setting
The central Mediterranean area marks the broad collisional boundary between the African and the Eurasian plates. The geodynamic characteristics of this region are driven by lithospheric blocks showing different structural and kinematic interaction, including subduction, back-arc spreading, and fold-and-thrust belt development (Fig. 1). The active dynamics of Italy is shown by the distribution of seismicity and GPS velocities fields, which outline the major deformation belts of the Alps and of the Apennines in peninsular Italy and Sicily (Fig. 2).
The transition between the Apennines and Western Alps occurs north of the Ligurian Sea (Fig. 1). In contrast, the Adriatic Sea and surrounding promontories represent the remaining part of the Adriatic lithospheric block caught between Europe and Africa and serving as the foreland domain of the Southern Alps, Dinarids and Apenninic thrust belts (Fig. 1; Royden et al., 1987; Carminati et al., this issue). Similarly, the Ionian Sea straddles the transition between the front of the Hellenids and Apennines across the Adriatic continental and Ionian transitional or oceanic lithosphere.
The Tyrrhenian back-arc basin opened and migrated eastward behind the Apennines in the wake of the retreating Adriatic–Ionian slab (Malinverno and Ryan, 1986). Today, seismic tomography and deep earthquakes beneath the south-eastern Tyrrhenian Sea identify the subducted Ionian slab (Fig. 1; Selvaggi and Chiarabba, 1995; Chiarabba et al., 2008). During Quaternary, the eastern and southern margin of the Tyrrhenian basin experienced extension, which was locally accompanied by volcanism (Conticelli et al., this issue). Displacement along normal faults articulated the Tyrrhenian coast of mainland Italy and Sicily in a complex alternation of subsiding basins and uplifting rocky promontories (Mariani and Prato, 1992; Ferranti et al., 2006; Acocella and Funiciello, 2006).
Calabria and north-eastern eastern Sicily form the Calabrian Arc, which represents a forearc terrane emplaced above the NW dipping-Ionian slab (Fig. 1). During Quaternary, the entire region experienced vigorous uplift (Westaway, 1993; Miyauchi et al., 1994) accompanied by extensional faulting along the Tyrrhenian Sea margin and the chain axis (Ghisetti, 1992; Monaco and Tortorici, 2000). Seismogenic normal faulting is still acting today (Fig. 2). Uplift and attendant extension are interpreted as a response to stalling of slab retreat and consequent asthenospheric flow into the gap resulting from slab detachment (e.g. Westaway, 1993; Wortel and Spakman, 2000), as being supported by asthenosphere wedging beneath the decoupled crust (Gvirtzman and Nur, 2001), or as due to viscoelastic response to enhanced erosional flux from land to sea following the onset of glacial-interglacial cycles (Westaway and Bridgland, 2007). At the borders of the uplifting regions, recent shortening is recorded by morphotectonic, seismicity, and geodetic studies in northern Calabria-Basilicata (Ferranti et al., 2009; Caputo et al., 2010) and in northern Sicily (Pondrelli et al., 2006; Hollenstain et al., 2003; Argnani et al., 2007; Ferranti et al., 2008; Mattia et al., 2009).
The islands of Sardinia and Corsica are a detached fragment of the Alpine foreland and orogenic belt (Patacca and Scandone, 2007). The western and eastern side of this block have been effected by extensional tectonics related to the Oligocene–Miocene Ligurian–Balearic and Miocene–Pliocene Tyrrhenian sea rifting, respectively (Fig. 1). Today, both islands appear tectonically stable as indicated by the negligible seismicity rate (Barba et al., this issue). Regional geodetic networks show that the block is not moving with respect to Europe (Devoti et al., this issue), although limited horizontal residual motions occur in southern Sardinia (Ferranti et al., 2008) as a result of relative convergence with Sicily.