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S244 Int J Earth Sci (Geol Rundsch) (2010) 99 (Suppl 1):S243–S264

longer time periods owing to the short instrumental record
(Papanikolaou et al. 2005).
Seismological strain has the advantage of showing the
existence of sometimes still unrecognised active faults. On
the other hand, owing to the limitation of the temporal
windows of observation (*1,000 years for historical
seismicity and *25 years for instrumental seismicity), if
an earthquake had not occurred within this period, the
associated structure would remain unrecognised, in the
absence of other sources of information. The seismological
approach remains particularly interesting in areas where
quantitative geological data are missing or are insufficient
to allow a detailed fault/slip analysis.
In peninsular Italy and Sicily, seismic deformation is
prevalently concentrated within a narrow extensional belt
which extends along the axis of the Apennine mountain
chain, from northern Tuscany to Calabria and northern
Sicily (Fig. 1). Subordinate seismic activity characterises
the outer thrust domains of the northern Apennines, the
Calabrian–Ionian arc and mainland-southern Sicily, as well
as a narrow compressional strip in the southern Tyrrhenian
Sea offshore of northern Sicily (Fig. 1).
Moderate-to-large earthquakes indicate SW–NE exten-
sion perpendicular to the Apennine belt (Pondrelli et al.
2006), with average extension rates estimated from seismic
moment summation of recent and historical earthquakes
ranging from 1 to 3 mm/year (Anderson and Jackson 1987;
Jackson and McKenzie 1988; Pondrelli et al. 1995;
Selvaggi 1998) up to 5–6 mm/year (Westaway 1992).
Summed geological extensional rates computed across the
central Apennines range between values of *2 mm/year Fig. 1 Regional seismotectonic framework of the study areas, with
first-order active compressional and extensional domains and major
(Visini et al. 2008) and *4.0 mm/year (Roberts and
earthquake focal mechanisms (M w C4.5; 1977–2004). The upper inset
Michetti 2004; Papanikolaou et al. 2005). shows the locations of Fig. 1 and schematises the outer front of the
Whereas the geometry and dimension of the intra-A- Neogene–Quaternary Apennine–Maghrebian fold-and-thrust system
pennine extensional process are fairly well agreed in the
literature, active compression at the front of the Apennine summation of seismic moment tensors from instrumental
fold and thrust belt of Italy is a highly debated topic, events indicate a SW–NE shortening rate in the range of
especially in terms of spatial continuity and amplitude 0.3–0.5 mm/year along the Padanian–Adriatic arc (West-
(Frepoli and Amato 1997; Coward et al. 1999; Finetti et al. away 1992). The seismic deformation rates computed for
2001; Di Bucci and Mazzoli 2002; Savelli et al. 2002; Sicily differ from one author to the next, showing up to
Lavecchia et al. 2003; Vannoli et al. 2004; Pondrelli et al. fivefold difference. Kiratzi (1994) evaluated an average
2006; Lavecchia et al. 2007a, b; Boncio and Bracone shortening of 1 mm/year in the NNE–SSW direction across
2008). the entire island of Sicily and its northern offshore. Jenny
Regional-scale focal mechanism data and borehole et al. (2006) considered separately the mainland-southern
breakouts show active compression across the Padanian Sicily area and the Tyrrhenian offshore area and for both
arcs and the Marche–Adriatic arc in central Italy, the Sci- of them computed an average NW–SE shortening of
acca–Gela–Catania arc in mainland-southern Sicily and 0.1–0.2 mm/year.
across the narrow E–W striking strip off the northern coast On the basis of continuous and/or survey-mode GPS
of Sicily in the southern Tyrrhenian Sea (Montone et al. data, some authors have computed active compression
2004; Chiarabba et al. 2005; Neri et al. 2005; Jenny et al. across the Padanian arcs in the SW–NE direction at a
2006; Lavecchia et al. 2007a, b). velocity of 0.8 mm/year (Serpelloni et al. 2005), across the
Seismic strain rates computed by means of scalar Marche–Adriatic arc in the SW–NE direction at a velocity
seismic moments from historical earthquakes and/or of 1.6 mm/year (Devoti et al. 2008), across mainland-

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