Patterns of tectonic stress in Sicily from borehole breakout observations and finite element modeling

The orientation of in situ tectonic stress was deduced from borehole breako ut analysis of 22 wells from onshore Sicily. The results allow us to distin guish the stress field of different geological units: (1) A nearly NNW (148 degrees) orientation is detected in the Hyblean Plateau. (2) A NNE SHmax d irection characterizes the Gela area. To the north, within the thrust belt (around Mount Judica), the SHmax direction swings to NE. In the northeaster n segment of the foredeep, the Catania Plain, the direction of SHmax is rou ghly parallel to the NE trending grabens that mark the northern margin of t he Hyblean Plateau. (3) The southwestern segment of the foredeep has no pre ferential SHmax orientation and may act as a transition zone with isotropic horizontal stresses. (4) In western Sicily a SHmax orientation from N-S to NW-SE is observed. This fits well the kinematics of the SE migrating Egadi and Adventure thrust belts and the direction of shortening inferred from t he modern seismicity of the area. A three-dimensional finite element modeli ng, including the most important tectonic features, was performed. Modeling results of the stress field indicate that the NNW trending SHmax is locall y influenced by the variation of crustal thickness and local zones of weakn ess. In addition, the Pantelleria Rift causes a rotation of the regional NW -SE stress orientation to NNE along the northern rim of the rift system, in cluding large on-shore areas in the adjacent central south Sicily.