Geological and seismological clues for a regionally-extended crustal discontinuity in central-eastern Sicily (Italy)

Abstract

An integrated analysis of large scale geological features and seismological data provides clues for a regionallyextended structural discontinuity slicing through all over the central-eastern portion of the Sicilian Fold and Thrust Belt, between the Madonie Mts. range and south of Mt. Etna region. Along this area, major NE-SW trending Mio-Pliocene compressive structures (thrust-top basins and related syncline) are systematically dragged and rotated according to vertical axis until to assume a hook-shape at their terminations. The clockwise sense of rotation of such major structures suggests the occurrence of regional, more than 100 km long, dextral wrench fault zone with a NW-SE direction. More detailed field surveys performed in key sectors (e.g. Madonie Mts. and Mt. Judica region) reveal that this crustal discontinuity consists probably of a wider deformation band that in the near-surface scattered into a series of discrete segments which sometimes overlap to form zone of releasing/restraining stopovers. The analysis of the seismicity of the studied region helped us to achieve further information about the characteristics of this shear zone. Selected earthquakes (from the CSI 1.1 1981–2002 by Castello et al., 2006, and from Bollettino Sismico 2003-2012, http://bollettinosismico.rm.ingv.it/index.php), were used as data source for a simultaneous inversion of a 3-D velocity structure and hypocentre parameters. The obtained velocity images and the foci distribution depict a relevant NW-SE oriented tectonic boundary. This structural element splits a sector of high concentration of earthquakes northwards from a zone with relative paucity of seismicity southward. Further, the possible presence of this major structural discontinuity is emphasized by a strong wave velocity contrast found in central Sicily and visible down to about 30 km of depth.