Estimates of stress directions by inversion of earthquake fault- plane solutions in Sicily

Abstract

The tectonic stress orientation is estimated in the lithosphere of northern Sicily, the southern Tyrrhenian sea and southern Calabria, and in the Wadati-Benioff zone below the Tyrrhenian, by inversion of fault-plane solutions of earthquakes covering a magnitude range from 2.5 to 7.1. Focal mechanisms of 97 earthquakes are taken from the literature, after a critical evaluation of their data quality. An average misfit of F = 13° indicates that the set of all shallow (<50 km) earthquakes is generated by a heterogeneous stress field. The earthquakes with M ≥5 define a regional stress field with the greatest principal stress, σ1, dipping at a shallow angle to the south. In north-eastern Sicily and south-western Calabria the stress field estimated by earthquakes is extensional, with σ3 in a direction of WNW, and a near-vertical σ1, in agreement with the graben tectonics mapped geological in this area. The earthquakes in the Wadati-Benioff zone define σ1 dipping at about 70° to the NW, subparallel to the zone, with σ2 horizontal and striking parallel to the zone. -from Authors