GNGTS 2013 - Atti del 32° Convegno Nazionale

fault system running offshore, sub-parallel to the Ionian coast, where it has reactivated the Malta Escarpment (Bianca et al. , 1999; Palano et al. , 2012). Accordingly, the overall oro- genic belt along the eastern Sicily coastal sector has been affected by a rift-driven vigor- ous tectonic uplift, with rates progressively decreasing south- wards from about 2 mm/yr to 1 mm/yr, that, combined with relative sea-level change, has caused the terracing of fluvial and coastal deposits (Ferranti et al. , 2006; Spampinato et al. , 2012; Ristuccia et al. , 2013). Current tectonic activity is also responsible for the destructive historical earthquakes (M≥7) that occurred in south-eastern Sicily (e.g. 1169 AD, 1693 AD events, Boschi et al. , 1995). The location of seismogenic sources is a topic still widely debated: normal faults located along the Ionian offshore (see Bianca et al. , 1999 and references therein) and/or compressional structures located to the north and to the south of the Catania Plain, between the front of the chain and the northern margin of the Hyblean foreland (see DISS Working Group, 2010). Seismicity. We analyzed distribution and kinematics of the earthquakes located in the south- ern and western sectors of Etna, between the chain, to the north, and the margin of the Hyblean Foreland, to the south (Fig. 1a).We excluded the events located in the eastern sector of the volcano to prevent that the shallow seismicity related to the extensional structures could complicate our analysis. About 2000 earthquakes, with a magnitude ranging between 1.0 and 4.3 and recorded by a local network between 1994 and 2012, were selected from the “ Catalogo dei terremoti della Sicilia Orientale - Calabria Meridionale. INGV, Catania ”, (further details about the catalogue at: http://www.ct.ingv.it/ufs/analisti/catalogolist.php) .More accurate hypocentreswere obtained by relocating the events with advanced techniques, by using a 3D velocity model (fromChiarab- ba et al. , 2004; Patanè et al. , 2006) and the software tomoDDPS (Zhang et al. , 2009), that pro- vide results with fewer uncertainties than those produced by the use of more simple algorithms. The distribution of earthquakes shows a clear trend of the seismic events to deepen from very shallow hypocenters in the area south of Etna, down to a depth of about 35 km to the NNW (Fig. 1b). The analysis of the fault plane solutions (see also Scarfì et al. , 2013) indicate that the majority of the events are strike-slip or oblique type. Furthermore, a careful analysis of the direction of the principal stress axes (P-axes) reveals that at the shallower and intermediate levels (down to 5 and 10 km), the stress field is inevitably influenced by the deep magmatic system of the volcano, the greater is the proximity to crater area. At greater depths, the regional dynamics is the main driving force with the P-axes NW-SE oriented (Fig.1a). Gps data. In 1992 the IGMI (Italian Military Geographical Institute - www.igmi.org) started the GPS measuring of a network made up of 1260-bechmarks, extended over the whole Italian area. We have reoccupied three IGMI benchmarks north and south the Catania Anticline (Figs. 1a and 2) in order to calculate the velocities map of some benchmarks very close to the alignment revealed by interferometric data. The GPS survey was carried out by using Leica GX1220 receivers and AR10 antennas, while instruments used by the IGM in Fig. 2 – Velocity map (1994-2013) of the IGM GPS benchmarks. 50 GNGTS 2013 S essione 1.1