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

Fig. 6. Instrumental earthquakes with Ml≥2.5 occurring between 1981 and 2006 within the grey area above the SBT 0-to-30 km depth-contour lines.
Source of data: CSI 1.1 catalogue (Castello et al., 2006) for the time interval 1981–2002 and Bollettino Sismico from 2003 to 2006; adopted selection
criteria: depthb40 km; RMSb0.5s, gapb200°, phase readingsN10. The fault plane solutions refer to earthquakes with moment magnitude M w N4.0
occurred since 1968 within the grey study area (A&J87 = Anderson and Jackson, 1987; F&A = Frepoli and Amato, 2000; P&AL = Pondrelli et al.,
2004). The lower left-lateral inset shows a number of focal mechanisms computed by Castellano et al. (1997) and by Neri et al. (2005a) for events
with Ml N 3.0, located beneath the Etna volcano at depths N 10 km (C1 = 23/09/1989 09:28; C2 = 23/10/199121:36; C3 = 23/10/1991 21:44; C4 = 23/
09/1989 13:17; C5 = 03/08/1989 08:30; C6 = 03/08/1989 08:30; C7 = 19/06/1988 01:44; N1 = 13/08/1988; N2 = 20/11/2000; N3 = 12/10/1993; N4 =
10/02/1995). Starting from these data, and applying a Linked Bingham Statistic procedure, the Average Deep Etna focal mechanism shown within the
inset and the associated P-axis (trend: N170°E, dip: sub-horizontal) have been calculated. The shear-minimum (Sh min ) axes refer to a selection of
quality A and B borehole breakout data in Montone et al. (2004).

recognition of early Pleistocene deposits onlapping both compression and tectonic inversion of the northern
the SBT thrust front and the foreland terrains (Butler border fault of the Lentini Pleistocene graben, at the
et al., 1992; Grasso et al., 1995; Lickorish et al., 1999). outer front of the Gela–Catania thrust plane, have been
On the other hand, some authors have highlighted an also pointed (Catalano et al., 2006). Additionally, an
ongoing activity of the SBTand its inner splay. Bousquet incipient northward-dipping reverse shearing plane,
and Lanzafame (1986), first, and other researchers cutting obliquely through the Pleistocene sediments,
subsequently (Lanzafame et al., 1997; Carbone et al., has been identified in seismic lines within the southern
2000; Monaco et al., 2002; Catalano et al., 2004) have Catania plain (Torelli et al., 1998). Some indication of
documented late Pleistocene–Holocene nearly N–S late Quaternary activity is also given in the literature for
compression in central-eastern Sicily, with a shortening the inner splay of the SBT, in correspondence of the
of a few kilometres at the frontal portion of the thrust belt Settefarine thrust (Grasso et al., 1995) and of the Sciac-
and with formation of WSW–ENE trending fault ca–Mt. San Calogero thrust (Monaco et al., 1996). The
propagation folds deforming the sedimentary substratum hypothesis of active compression also along the Ionian
of the Mt. Etna volcano. Evidences of late Quaternary thrust front, north-eastward prosecution of the Sicilian