Orientations of the strain main axes in the lithosphere of Sicily and surroundings as deduced from earthquake data

Kostrov\'s method has been used to estimate strain tensor orientations in a rock volume including the lithosphere of Sicily, southen Tyrrhenian and westen Ionian. Basic data for the investigation (magnitudes and fault plane solutions of the strongest regional earthquakes) were taken from the literature. We found that most of the study area is characterized by a nearly horizontal north-south maximum shortening similar to that reported by previous investigators for smaller lithospheric volumes in the same area. In addition, our attempts to evaluate the strain orientation uncertainties (the first in the literature for Sicily and surroundings) revealed a level of constraint clearly worse for the minimum shortening axis ε3 (practically unconstrained in an E-W vertical plane) compared to that found for the maximum shortening axis ε1. We propose that a roughly north-south Africa-Europe convergence, together with a high degree of structural heterogeneity in the rock volume under investigation, may explain both the ε1 orientation and the large extent of the confidence area obtained for ε3 This is in agreement with the available structural maps (indicating the prevailing presence of nearly E-W reverse and NW-SE dextral strike-slip faults) and supports tectonic models locally assuming a low-velocity plate convergence along a direction between NNW-SSE and NNE-SSW.