What seismicity offshore Sicily suggests about lithosphere dynamics and microplate fragmentation models in the Central Mediterranean

We analyze an updated dataset of earthquakes of Southern Italy, focusing in particular on hypocenter locations and seismogenic stress distributions in the southern and eastearn offshores of Sicily, the two sectors of the study region where seismic and geodetic information needed for geodynamic modeling is still poor because of poor geometry of monitoring networks. Using Bayesian non-linear methods for hypocentral locations and hypocenter error estimates we improve the earthquake locations performed by more traditional linearized techniques, and this helps us to make significant progress in the interpretation of seismicity and seismogenic stress distributions especially where seismometric network geometry is more critical. Epicenter maps and hypocenter vertical sections, together with (i) best quality focal mechanisms coming from seismic waveform inversion and (ii) orientations of stress principal axes estimated by inversion of focal mechanisms, help us to better recognize geodynamic engines and plate margin deformation in the study area. NW-trending convergence between Africa and Eurasia is recognized as the main source of tectonic stress in the study region, producing clearly detectable signatures in terms of σ1 orientations also in the offshore sectors of the western Ionian and the Sicily Channel. Seismicity and seismogenic stress tensor highlight nearly uniform compressional dynamics related to plate convergence in the Sicily Channel, in contrast to rifting and microplate divergence proposed in that sector by other investigators. In the western Ionian, seismicity and stress inversion results reveal superposition of convergence-related compression and extensional dynamics. The latter, characterized by minimum compressive stress oriented SW-NE, can be related to a rifting process (opening SW-NE) hypothesized by previous investigators on the basis of marine geophysics analyses performed between the Alfeo-Etna and the Ionian Faults. The seismicity and seismogenic stress detected in the Western Ionian show that assumptions of microplate rigidity in this area made by previous workers when modeling poor geodetic data available can be inappropriate. Our findings indicate that more complex rheologic models should be adopted for reconstruction of tectonic deformation and microplate relative motions in the Central Mediterranean region.