An integrated approach to investigate the seismotectonics of northern Sicily and southern Tyrrhenian

This paper deals with a comparison among recent structure and seismicity in the hinge zone between northern Sicily and southern Tyrrhenian, corresponding to both emerged and submerged northern portion of the Maghrebian chain. This hinge zone is part of a wider W–E trending right-lateral shear zone, mainly characterized by both a synthetic NW-SE/W–E oriented, and antithetic left-lateral N–S/NE-SW fault systems, which has been affecting the tectonic edifice, since the Pliocene. The inland structures have been mapped using aerial-photo interpretation, geological mapping and mesostructural analysis to reconstruct the stress regime in the study area. On the contrary, the offshore structures have been inferred from the available morpho-bathymetric and geological maps of the southern Tyrrhenian basin. A seismological analysis was carried out on a data set of about 11,000 seismic events occurred between January 1981 and December 2005 in the study area. The observed local magnitude is mainly comprised between 2.0 and 2.3, reaching in places peak values greater than 5.5. The distribution of the hypocenters allowed to recognize three major seismogenic zones. The deepest events (down to about 600 km) of the easternmost area are related to the Ionian lithospheric slab subducting beneath the Calabrian arc. A set of events is substantially depending by the Etna volcano activity. The third set of events is heterogeneously distributed mainly in the southern Tyrrhenian and in the eastern Sicily. This latter seismogenic zone is strictly connected to the deformation field active within the hinge zone. A statistical analysis of the seismological data allowed to individuate several clusters of events occurred in the hinge zone, which have been subsequently relocated with a relative location method. Furthermore, the seismogenic processes, relative to the most numerous clusters, were characterized in the space, time and magnitude domains with statistical techniques. The collected focal mechanisms, even if highlight the complexity of the relationships between seismogenic volumes of the clusters and single dislocations, also showsomespatial trends useful to the seismotectonic analysis. On the whole, both structural and seismological data seem to be consistent with a neotectonic model related to NW-SE trending maximum compressional stress axis producing a non-coaxial strain, even if in particular areas different seismogenic conditions are possible, due to the accommodation of rock volumes leading a marked mechanical heterogeneity.