An intense tectonic activity in eastern Sicily and southern Calabria is well documented by the differential uplift of Late Quaternary coastlines and by the record of the strong historical earthquakes (1693, south-eastern Sicily; 1783 southern Calabria; 1818, Catania; 1865, Etna; 1908, Messina Strait; 1990, Augusta). The extensional belt that crosses this area is dominated by a well established WNW-ESE-oriented extensional direction. However, this area is largely lacking of any structural analysis able to define the tectonics at a more local scale. In the attempt to fill this gap of knowledge, we carried out a systematic analysis of extension joint sets. Indeed, the systematic field collection of these extensional features, coupled with an appropriate inversion technique, allows to infer the causative tectonic stress field. Joints are defined as outcrop-scale mechanical discontinuities showing no evidence of shear motion and being originated as purely extensional fractures. Such tectonic features are one of the most common deformational structures in every tectonic environment and particularly abundant in the study area. A particular arrangement of joints, called "fracture grid-lock system", and defined as an orthogonal joint system where mutual abutting and crosscutting relationships characterize two geologically coeval joint sets, allows to infer the principal stress directions and the stress ratio. We performed the analyses of joints only on Pleistocene deposits of Eastern Sicily and Southern Calabria. These deposits represent the infilling of Pliocene-Pleistocene basins controlled by the activity of the main fault system and consist essentially of shallow marine or transitional sediments. Moreover we investigated only calcarenite sediments and cemented deposits, avoiding claysh and loose matrix-supported clastic sediments where the deformation is generally accomodated in a distributed way through the relative motion between the single particles. In the selection of the sites, we also took into account the possibility to clearly observe the geometric relationships among the joints. For this reason we chose curvilinear road cuts or cliffs, wide coastal erosional surfaces and quarries. The numerical inversions show stress tensors similar at all the investigated sites. Indeed, the maximum principal stress axis σ1 is always vertical or subvertical, while the intermediate and the least axes (σ2 and σ3) lie on the horizontal plane or show low plunging values. The main direction of extension (σ3) at each site is in general agreement with the first-order regional stress field (WNW-ESE) even though some local perturbations have been recognized. These are interpreted as due to interferences between large active faults and their particular geometrical arrangement. In particular local stress deflections and stress swaps systematically occur in zones characterized by two overlapping fault segments or close to their tips.
Scheda prodotto non validato
Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo
|Titolo:||Quaternary and active tectonics along the Tyrrhenian coast of Sicily and Calabria.|
|Data di pubblicazione:||2014|
|Appare nelle tipologie:||04.1 Contributi in atti di convegno (in Rivista)|