Crustal structure and fault kinematics between the Aeolian Arc and the Ionian Sea offshore as revealed by earthquake tomography and focal mechanisms stress inversion

Abstract

We studied the ongoing tectonics of the region extending between the Aeolian Arc and the Ionian Sea offshore, including the southern Calabria and the north-eastern Sicily, through an in-depth analysis of seismological data. For this area, recent studies have shown a very complex tectonic framework, fragmented into crustal blocks separated by seismically active belts and characterized by neighbouring collisional, subduction and active volcanic (Etna and Aeolian Arc) domains. Contraction affects mainly the western sector with an E-W oriented compressive belt extending from the Aeolian archipelago to the Ustica Island. Conversely, the eastern sector (i.e. NE Sicily and western Calabria) is dominated by Late Quaternary extensional deformation. The definition of the seismogenic sources in this area is a difficult task and a matter of intense debate, mainly because morphological expressions of the faults are not evident, since the terrains traverse make it more difficult to keep track of faulting activity, and because there are difficulties in recognizing geological formations and tectonic structures at the great depth reaching the Tyrrhenian and Ionian Seas. In our study, a selected dataset consisting of more than 4000 small-to moderate-magnitude earthquakes (1.0≤ML≤4.8), collected in two decades by a local seismic network, were used to perform a simultaneous inversion of both 3D velocity structure and earthquake locations, in order to trace the characteristics of the faulting systems. The obtained velocity images and the foci distribution depict relevant structural features at depth. In particular, velocity anomalies and hypocentres highlight some WNW-ESE to NW-SE lineaments between the Aeolian Islands and the Ionian Sea. In addition, the fault plane solutions for the best recorded earthquakes were determined and used to resolve the current local stress fields and to characterize the faulting regime of the main seismogenic sources. The results were combined to achieve a coherent geodynamic scheme and to better characterize the active tectonics of the region.