GNGTS 2016 - Atti del 35° Convegno Nazionale

200 GNGTS 2016 S essione 1.2 predominant component of stress is extensional, with an evident rotation from NW to NE of the principal stress axes (σ 1 ). In the Etnean area some thrust, strike slip, and also unresolved regime highlight an area of complex stress distribution (NW-SE σ 1 in the northwest sector and W-E in the eastern part), as also confirmed by the increase of the variance (Fig. 2). Conclusive remarks. The obtained velocity images and the foci distribution depict relevant structural features at depth, striking WNW-ESE to NW-SE and NE-SW, between the Aeolian Islands, the Messina Strait and Mt. Etna Volcano. In particular, a WNW-ESE faults system in the northern sector of the Aeolian Islands is outlined. It shows dextral strike-slip motion and transpressive zones in response to the NW–SE oriented regional compression. From its eastern termination, the faults belt develops through northeastern Sicily and the Ionian Sea. The seismic pattern indicates a NW-SE dextral strike-slip motion in the offshore areas and a NE-SW or NW-SE normal slip on mainland. These crustal structures are the shallow expression of a main lithospheric-scale tear highlighted by the seismic characteristics that depict a NW-SE structure accommodating the sinking and narrowing Ionian slab. As a whole, these fault systems form a transfer zone linking the active thrust fronts in the Tyrrhenian and Ionian compartments. In response to the slab dynamics, the active tectonics of the Peloritan-Calabrian area indicates NW- SE extension. On the other side, in northeastern Sicily, below a normal faults regime, the likely expression of a stress reorganization consequent to the slab segmentation and detachment, an active contraction drives the deformations, in agreement with the Eurasia–Nubia convergence. References De Guidi G., Barberi G., Barreca G., Bruno V., Cultrera F., Grassi S., Imposa S., Mattia M., Monaco C., Scarfì L. and Scudero S.; 2014: New Geological, seismological and geodetic evidence of active thrusting and folding south of Mt. Etna (eastern Sicily): revaluation of “seismic efficiency” of the Sicilian Basal Thrust. Rend. Online Soc. Geol. It., Suppl. 1, 31. Fig. 2 – Orientations (lower- hemisphere projection) of the principal stress axes obtained by inverting: a) the 183 crustal FPSs and b) the subset for the three sectors identified (see dotted lines and letters in c)). Grey areas indicate the 95% confidence limits of σ 1 and σ 3 orientations. c) Bars indicate the orientation of the σ1 (note that their length is not proportional to the inclination) obtained by inverting the focal mechanisms by Michael’s approach (Michael, 1987), inside a radius of 14 km around the grid nodes, 10 × 10 km spaced (black dots; see text for further details). Abbreviations are: NF, normal fault regime; NS, normal strike; SS, strike-slip; TS, thrust-strike; TF, thrust fault; U, undefined stress regime. The variance of the stress tensor at each node is color-coded, with blue (low values) to red (high values) colors indicating a higher variance (heterogeneous stress field).