Geodetic and geological evidence of active tectonics in south-westernSicily (Italy)

Abstract

Integrated geological, geodetic and marine geophysical data provide evidence of active deformation insouth-western Sicily, in an area spatially coincident with the macroseismic zone of the destructive 1968Belice earthquake sequence. Even though the sequence represents the strongest seismic event recordedin Western Sicily in historical times, focal solutions provided by different authors are inconclusive onpossible faulting mechanism, which ranges from thrusting to transpression, and the seismogenic sourceis still undefined. Interferometric (DInSAR) observations reveal a differential ground motion on a SW–NEalignment between Campobello di Mazara and Castelvetrano (CCA), located just west of the maximummacroseismic sector. In addition, new GPS campaign-mode data acquired across the CCA alignment doc-uments NW–SE contractional strain accumulation. Morphostructural analysis allowed to associate thealignment detected through geodetic measurements with a topographic offset of Pleistocene marine sed-iments. The on-land data were complemented by new high-resolution marine geophysical surveys, whichindicate recent contraction on the offshore extension of the CCA alignment. The discovery of archaeo-logical remains displaced by a thrust fault associated with the alignment provided the first likely surfaceevidence of coseismic and/or aseismic deformation related to a seismogenic source in the area. Resultsof the integrated study supports the contention that oblique thrusting and folding in response to NW–SEoriented contraction is still active. Although we are not able to associate the CCA alignment to the 1968seismic sequence or to the historical earthquakes that destroyed the ancient Greek city of Selinunte,located on the nearby coastline, our result must be incorporated in the seismic hazard evaluation of thisdensely populated area of Sicily.