Fault plane solutions of crustal earthquakes in Southern Italy (1988-1995): seismotectonic implications

Abstract

The Southern Apennines and the Sicilian-Calabrian regions belong to the complex geodynamic Central Mediterranean area, which is dominated by the NNW-SSE convergence of the European and African plates and is strongly affected by the presence of Neogene-Quaternary subduction/collision arcs and related back-arc basins In order to obtain a more detailed picture of the processes active in these two regions, we calculated 173 new fault plane solutions of crustal events with 2.5 < M < 4.4 recorded by the national seismic network of the Istituto Nazionale di Geofisica in the period 1988-1995. Normal and strike-slip solutions are largely prevalent in the Southern Apennines, with tensional (T) axes mostly oriented NE-SW, perpendicular to the belt, in agreement with active stress directions from breakouts. In the Sicilian region the seismicity is concentrated in the eastern portion of the island. Different focal mechanism categories are present in the Nebrodi and Etna sector indicating a complex strain release in these two regions. Thrust and strike-slip solutions prevail in the Aeolian Islands associated with ~ N-S compression, whereas in Western Sicily the prevailing orientation of P-axes is around WNW-ESE. Although not well constrained due to only a few data in the region, there is a hint of active compression at the outer front of the Calabrian arc, in the Ionian Sea. The observed pattern of fault plane solutions suggests that the transition between oceanic subduction beneath Calabria and continental subduction in Sicily and in Southern Apennines controls the active tectonics of Southern Italy.