GNGTS 2013 - Atti del 32° Convegno Nazionale

New seismological, structural and marine geology constraints for a seismotectonic model of the hinge zone between northern Sicily and southern Tyrrhenian P. Capizzi, A. Giorgianni, G. Giunta, D. Luzio, R. Martorana, S. Orioli, A. Sulli DiSTeM Department, University of Palermo, Italy Northern Sicily and its Tyrrhenian off-shore are located in a very complex geodynamic context, where both the Sicilian-Maghrebian belt, associated to the collision between African and European Plates, and the more recent opening Tyrrhenian Basin coexist (Scandone et al. , 1979; Finetti and Del Ben, 1986; Malinverno and Ryan, 1986; Patacca et al. , 1990; Faccenna et al. , 1996; Monaco et al. , 1998; Giunta et al. , 2000b; Pepe et al. , 2000; Lo Iacono et al. 2011). This area represents therefore an important hinge zone between the two previous geodynamic elements evolving together since late Pliocene, which is part of a wider W–E trending right- lateral regional shear zone, extending for about 300 km from the Ustica-Eolie alignment to the Pantelleria rift. The Northern Sicilian-Maghrebian chain courses WE from Trapani Mts to the Peloritani Mts and is composed by a set of tectonic units deriving from the deformation of the Northern African Continental Margin. The architecture of the tectonic edifice, from the Late Oligocene, is the result of three main tectonic phases, characterized by compressional, extensional, and transcurrent tectonics (Giunta et al. , 2000b). The first compressional phase, responsible for the building of the thrust belt, is represented by fold associations, cleavage and foliation, thrust and contraction, which shortened the original paleo-tectonic domains forming flat-ramp, duplex, enveloping, and breaching geometries. This deformational style persisted, in the most internal sector of the thrust belt, until the Late Miocene. At that time the activation of low-angle top-to-the-north extensional faults produced a general stretching of the belt by re-orientation and inversion of pre-existing structures. The recent pattern of the Sicilian Maghrebides has been interpreted as an effect of a complicated grid of neotectonic high-angle strike-slip faults, which have been affecting the tectonic edifice since the Pliocene (Boccaletti et al. , 1990a; Nigro, 1998; Giunta et al. , 2000a; Renda et al. , 2000), identifying a hinge zone between emerged Sicilian orogen, with a moderate thickened crust, and the southern Tyrrhenian, characterized by crustal thinning. Starting from the Pleistocene is also active a Tyrrhenian verging extensional net and dip slip system, over imposed to previous transcurrent one, which accommodates the recent uplift of the emerged sectors of the chain. The brittle neotectonic pattern has been reconstructed on detail in the northern emerged areas of the Sicilian chain, where two main high-angle strike-slip systems occur, respectively NNW-SSE to W-E mainly right-lateral, and N-S to NW-SE left-lateral one (Fig. 1). The structures occur from the kilometer to the meter scales and seem to control the recent evolution of the northern Sicilian coastline, determining the formation of either uplifting restraining zones, coinciding with the main morphostructural highs, and the interposed coastal plains located in the tectonic depressions along the subsiding releasing areas. The interpretation of recent morphobatymetric maps allows to infer the neotectonic pattern also in the submerged areas, which highlights the continuity of the main morphostructural element between the emerged and submerged sectors, and the general coherence of the structural lineament trends controlling the genesis and the evolution of the main plio-pleistocenic clastic sedimentation areas (Giunta et al. , 2004). In the hinge zone between the Northern Sicily chain and the Tyrrhenian basin the earthquake hypocenters distribution highlights the presence of two main types of seismicity (Giunta et al. , 2002b, 2004, 2008; Gueguen et al. , 2002): the first one, characterized by deep hypocenters (down to about 600 km) affecting the easternmost sector of the area, is associated 154 GNGTS 2013 S essione 1.2