An integrated approach to investigate the seismotectonics of northern Sicily andsouthern Tyrrhenian

This paper deals with a comparison among recent structure and seismicity in the hinge zone betweennorthern Sicily and southern Tyrrhenian, corresponding to both emerged and submerged northern portion ofthe Maghrebian chain.This hinge zone is part of a wider W–E trending right-lateral shear zone, mainly characterized by both asynthetic NW-SE/W–E oriented, and antithetic left-lateral N–S/NE-SW fault systems, which has beenaffecting the tectonic edifice, since the Pliocene.The inland structures have been mapped using aerial-photo interpretation, geological mapping andmesostructural analysis to reconstruct the stress regime in the study area. On the contrary, the offshorestructures have been inferred from the available morpho-bathymetric and geological maps of the southernTyrrhenian basin.A seismological analysis was carried out on a data set of about 11,000 seismic events occurred betweenJanuary 1981 and December 2005 in the study area. The observed local magnitude is mainly comprisedbetween 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 subductingbeneath the Calabrian arc. A set of events is substantially depending by the Etna volcano activity. The thirdset of events is heterogeneously distributed mainly in the southern Tyrrhenian and in the eastern Sicily. Thislatter 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 inthe hinge zone, which have been subsequently relocated with a relative location method. Furthermore, theseismogenic processes, relative to the most numerous clusters, were characterized in the space, time andmagnitude domains with statistical techniques.The collected focal mechanisms, even if highlight the complexity of the relationships between seismogenicvolumes 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 toNW-SE trending maximum compressional stress axis producing a non-coaxial strain, even if in particular areasdifferent seismogenic conditions are possible, due to the accommodation of rock volumes leading a markedmechanical heterogeneity.