GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 1.1 29 the southern flank of Mt. Etna. The northern prosecution of the seismic line pictures a thickened crust sector, which consists of two superimposed distinct crusts. This part of the seismic lines can be interpreted, taking into account that the cross-section cuts parallel to the hinge of the Ionian subduction zone. The deeper crustal horizon, whose top is at depth of 21 km, represents the flexured Ionian Crust (Vp 7.5 - 6 km/s) and the upper crustal horizon consists of the CalabrianArc continental crust (Vp 6.0 km/s) and its sedimentary cover (Vp 3.0 - 5.0 km/s). An intermediate, low-velocity layer (Vp 5.0-5.5 km/s), located at depth from 12 to 21 km is interleaved between the two superimposed crusts. The evolution of the Etna volcanism was clearly controlled by the existence of the Africa- Ionian tectonic boundary. The earlier emissions of tholeiitic products, ranging in age from 540 kyr to 225 kyr, were in fact localised at the main transtensional features that were active along the southern margin of Mt. Etna (Catalano et al. , 2004), while the following emissions of the alkaline products (< 225 kyr) mainly developed within the extensional domain, to the north of the transform zone. North-eastern Sicily. The north-eastern corner of Sicily, comprising the Peloritani and part of the Nebrodi Mountain Belts, form an uplifted crustal block (Peloritani Mobile Block; PMB in Fig. 2) that is now diverging from both the Sicily collision zone and the southern Calabria sector of the arc. The geodetic data in the Nubia reference frame (D’Agostino and Selvaggi, 2004) evidence that the NE Sicily diverges, with rates of about 5 mm/a along a N160 direction, from the rest of the Calabrian arc, which is still migrating towards the E. This relative motion is consistent with the rate and the direction of the extension obtained by the inversion of structural data on the fault planes in the Straits of Messina area, which are also fitting the focal mechanism of the 1908 event. The geodetic measurements in NE Sicily also evidence a NNE-ward divergence of the PMB from the rest of island, at rates of about 5mm/yr (see FOSS vs Nubia in D’Agostino and Selvaggi, 2004). Recent geological analyses carried out at the southern border of the PMB pointed out an active extensional fault belt, which remobilized segments of the previous NW-SE oriented dextral fault system, at the southern edge of the arc (Pavano et al. , 2015). This reactivated extensional feature has been related to the June-September 2011 seismic swarm in the area of Longi-Galati Mamertino. It consists of about 430 events that followed the 23/06/2011 event, characterized by a 4.1 magnitude (ISIDe Working Group, 2010). This main event provided a focal mechanism (Scarfì et al. , 2013) indicating a NNE-SSW oriented extension, matching that obtained by GPS data and structural analyses of rejuvenated fault planes (Pavano et al. , 2015). The PMB is contoured by marine terraces, which have been referred to successive OISs from 15 (570 kyr) to the OIS 3 (60 kyr) (Catalano and Cinque, 1995; Catalano and De Guidi, 2003; Catalano and Di Stefano, 1997). They undercut a raised transgressive, neritic-to-batial marine sequence that ranges in age from 900 to 600 yr (Naso sequence; Catalano and Di Stefano, 1997). The Naso sequence pre-dates the tectonic uplift of the PMB that started, thus, at about 600 yr. Along the entire Tyrrhenian coast of the PMB the strandlines of the marine terraces show a constant elevation that constrain an almost uniform uplift-rate of about 1.1 mm/yr, since 600 kyr B.P.. In particular, the strandlines of the marine terraces cross undisturbed the main NW-SE dextral fault segments that dissect the region (e.g. Tindari Fault). Along the Tyrrhenian coast, the tectonic boundary of the mobile block is evidenced by a sharp decrease in the elevation of the marine terraces, ranging in age from the OIS 15 (570 kyr) to the OIS 3 (60 yr). To the north of the mobile block, the active volcanic belt of the Eolian Islands, whose oldest products have been dated at about 225 kyr B.P. (Crisci et al. , 1991), is represented by the islands of Volcano, Lipari and Salina, that are located at the main releasing bends along a seismogenic NNW-SSE dextral shear zone (Catalano et al. , 2009). Discussion and conclusions. The active extensional belt which extends from southern Calabria to the south-eastern Sicily is composed by two branches (southern Calabria and south- eastern Sicily) deriving from the reactivation of older faults, which are now linked by faults that