Geodynamic implications of earthquake data in the southern Tyrrhenian sea

Abstract

Data from short-period seismic stations operating in Calabria, Sicily and the Aeolian Islands have been used to investigate earthquake properties of the southern Tyrrhenian lithosphere. The results have been analyzed, taking into account other geophysical and geological information available in the literature for the same region, with the main purpose of contributing to the definition of local geodynamic processes. Space distribution and focal mechanisms of earthquakes support the hypothesis of southeastward migration of the southern Tyrrhenian lithosphere, shared by several authors in their tectonic modelling of the area. We find that most seismicity appears to be related to two main faults crossing the Aeolian Island archipelago (Sisifo and Vulcano) and propose that these faults are important dislocation structures associated with the lithosphere migration process. We also give a detailed picture of the seismic behaviour of the above-mentioned fault systems by analyzing the earthquake depth distribution, focal mechanisms, seismic clustering and strain release. Some degree of activity was also detected at the eastern boundary of the southern Tyrrhenian area (Calabrian Arc). In particular, our results demonstrate that in this highly stressed zone of contact between different tectonic units (Tyrrhenian and Ionian basins) strain is released under seismic form up to depths of the order of 25 km in the crust and not just in the shallowest structures as proposed by other authors.