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146 G. Lavecchia et al. / Tectonophysics 445 (2007) 145–167

of a unique regional-scale seismogenic structure capable to connect the active deformation and the seismic activity of the western,
central and eastern areas of mainland Sicily and those of central-southern Sicily evidently has strong implications in terms of
seismic hazard assessment. In fact, it allows the definition of a new homogeneous compressional seismotectonic province, which
extends between the SBT surface front line and the surface projection of the 25 km SBT depth-contour line. A subdivision in two
sub-provinces, a shallow one above the 0–10 km SBT segment and a deep one above the 10-to-25 km SBT segment, is also
considered and the energy released of the associate earthquakes evaluated. To conclude, the proposed model is discussed in
comparison with other models from the literature and some important open problems are put forwards.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Tectonics; Active thrusting; Earthquake; Seismogenesis; Sicily; Southern Italy

1. Introduction in mainland and central-southern Sicily and to describe
such an eventual source from the point of view of the 3D
Reverse and reverse-oblique seismogenic deforma- geometry, its kinematics and the association with
tion, controlled by an average nearly N–S low-dip historical and instrumental earthquakes. Our approach
compressional stress tensor, is active both in western will be based on the merging of geological and
Sicily, where the Belice Valley 1968 seismic sequence seismological information toward a general seismotec-
occurred (equivalent moment magnitude reached nearly tonic interpretation. Moreover, we will not only take
6.1, Working Group CPTI, 2004), and in eastern Sicily, into consideration potentially active geological struc-
where an intense background instrumental seismic tures developed in Quaternary times, but we will
activity (magnitude up to 4.6) is recorded within the consider the long term, Miocene to Quaternary,
middle and lower crust beneath the Etna volcanic area geological context. In fact, it is our conviction that the
(Castellano et al., 1997; Patanè and Privitera, 2001; understanding of the deformation history and of the
Patanè et al., 2004; Monaco et al., 2005; Neri et al., tectonic style of the elements involved in the progressive
2005a). Beginning from these evidences, we investigate development of the Sicilian chain, may substantially
if they might be both results of expression of ongoing help to define and characterize the deep shape and the
compressional activity at the Sicilian front of the kinematics of the here investigate outermost basal
Apennine–Maghrebide Cenozoic orogenic belt (Fig.1). thrust, the SBT.
The Apennine–Maghrebide thrust system is active and
seismogenic along the Padanian–Adriatic thrust system 2. Tectonic setting
in northern-central Italy (Selvaggi et al., 2001; Lavec-
chia et al., 2003; Montone et al., 2004; Vannoli et al., 2.1. The structural map
2004; Piccinini et al., 2006) and possibly active along
the Ionian front offshore of Calabria (Cita et al., 1984; The Sicilian Apennines may be schematically des-
Hieke et al., 2005; Gutscher et al., 2006). The Sciacca– cribed as a southward-verging fold-and-thrust belt sys-
Gela–Catania front of the Sicilian sector of the belt has tem, developed since early Miocene times, through the
been considered to be inactive, at least since the Late progressive nucleation of major tectonic units which,
Pleistocene time by some authors (Butler et al., 1992; from north to south, involved stratigraphic successions
Grasso et al., 1995; Lickorish et al., 1999; Chiarabba pertaining to different Late Paleozoic to Cenozoic pa-
et al., 2005 among many others) and active, although leogeographic domains (Ghisetti and Vezzani, 1984;
only moderately seismogenic, by others (Cristofolini Catalano et al., 1989; Butler et al., 1992; Catalano et al.,
et al., 1985; Jenny et al., 2006; Lavecchia et al., 2006). 1994; Lentini et al., 1994; Nigro and Renda, 1999;
The occurrence of N–S lithospheric strike slip faults Montanari, 2000). Starting from mid-Miocene times,
within the Hyblean–Pelagian foreland has also been these stratigraphic successions were followed by syn-
considered, in an alternative to compression, to explain orogenic and late-orogenic sequences representing
the Belice earthquake in western Sicily, such as the migrating foredeep filling sediments and piggy-back
Hyblean earthquakes in eastern Sicily (Argnani, 1987; basins, which were also involved in the deformation.
Meletti et al., 2000). The entire system is now overthrusted above carbonate
This paper aims to verify if active thrusting along the platform deposits of the Hyblean–Pelagian foreland, the
outermost thrust of the Sicilian belt, here called Sicilian most advanced thrust front being the Sciacca–Gela–
Basal Thrust (SBT), is a reasonable seismogenic source Catania front (Figs. 1 and 2). Beneath the thrust plane,