GNGTS 2014 - Atti del 33° Convegno Nazionale

The analysis of the seismicity of the studied region helped us to achieve further information about the characteristics of this shear zone. Results point out a relevant NW-SE oriented seismic boundary that splits a sector of high concentration of earthquakes northeastwards from a zone with relative paucity of seismicity southwestward. Computed focal solutions revealed prevailing dextral strike-slip kinematics along this boundary. Further, the possible presence of this major structural discontinuity is emphasized by a strong wave velocity contrast found in central Sicily and visible down to about 30 km of depth. Tomographic sections (Fig. 2B) also revealed that the shear zone develops at transition between distinct continental crustal sectors, a thicker in the SW and a thinned (transitional to the Ionian domain) in the NE. Moreover, the shear zone is currently characterized by earthquakes with moderate magnitude although a destructive seismic event (M=6) occurred in the past (about 2ky ago) alongside the inferred shear zone (see Barreca et al. , 2010). This has strong implication in the seismic hazard of central-eastern Sicily. The occurrence of a narrow extensional area affecting the Nebrodi Mountains (Fig. 3), in agreement with previous seismologic (Neri et al. , 2005; Lavecchia et al. , 2007), geodetic (Devoti et al. , 2011; Palano et al. , 2012) and geological (Billi et al. , 2010) data can be variously interpreted i) as incipient extension as ensuing from upper crustal stretching above an active thrust belt (Lavecchia et al. , 2007), ii) as reactivation of pre-existing faults and upwelling of melt mantle material (Billi et al. , 2010) or, alternatively, iii) as a residual crustal STEP-related tearing in the upper plate. Anyway, the whole data set allow us to interpret this shear zone as a crustal discontinuity that probably played a role of STEP during Plio-Pleistocene times, and that currently contribute to the recent geodynamic reorganization in the south-central Mediterranean area (Goes et al. , 2004; Palano et al. , 2012). References Argnani, A., 2009, Evolution of the Tyrrhenian slab tear and active tectonics along the western edge of the Tyrrhenian subducted slab. in: van Hinsbergen, D.J. J., Edwards, M. A., Govers, R. (Eds.), Collision and Collapse at the Africa-Arabia-Eurasia subduction zone . Geological Society, Special Publication, v. 311, London, pp 193-212. Argnani, A., and Bonazzi, C., 2005, Malta Escarpment fault zone offshore eastern Sicily: Plio-Quaternary tectonic evolution based on new multi-channel seismic data : Tectonics, v. 24, TC4009, doi:10.1029/2004TC001656. Barreca G., Monaco C. 2013. Vertical - axis rotation in the Sicilian fold and thrust belt: new structural constrains from the Madonie Mts. (Sicily, Italy) . It. J. Geosci. (Boll. Soc. Geol. It.), vol. 132 N° 2 (2013)pp. 407-421. doi: 10.3301/IJG.2012.44 Barreca G., Barbano M.S., Carbone S. and Monaco, C. (2010) - Archaeological evidence for Roman-age faulting in central-northern Sicily: Possible effects of coseismic deformation, in Sintubin, M., Stewart, I.S., Niemi, T.M., and Altunel, E., eds., Ancient Earthquakes : Geological Society of America Special Paper 471, p.223–232, doi: 10.1130/2010.2471(18). Billi, A., D. Presti, B. Orecchio, C. Faccenna, and G. Neri (2010), Incipient extension along the active convergent margin of Nubia in Sicily, Italy: Cefalù-Etna seismic zone , Tectonics, 29, TC4026, doi:10.1029/2009TC002559. Devoti, R., A. Esposito, G. Pietrantonio, A. R. Pisani, and F. Riguzzi (2011), Evidence of large scale deformation patterns from GPS data in the Italian subduction boundary , Earth Planet. Sci. Lett., 311, 230–241, doi:10.1016/ j.epsl.2011.09.034. Dewey J.F., Helman M.L., Turco E., Hutton D.H.W. & Knott S.D. (1989) - Kinematics of the westwern Mediterranean. In: Coward M.P., Dietrich D. & Park R.G. (eds.), Alpine Tectonics, Geol. Soc. London Special Publication, 45, 265-283. Faccenna, C., Piromallo, C., Crespo-Blanc, A., Jolivet, L., and Rossetti, F., 2004, Lateral slab deformation and the origin of the western Mediterranean arcs : Tectonics, v. 23, TC1012, doi:10.1029/2002TC001488. Finetti, I.R., Lentini, F., Carbone, S., Del Ben, A., Di Stefano, A., Forlin, E., Guarnieri, P., Pipan, M., Prizzon, A., 2005. Geological outline of Sicily and Lithospheric Tectono-dynamics of its Tyrrhenian Margin from new CROP seismic data. In: Finetti, I.R. (Ed.), CROP PROJECT: Deep Seismic Exploration of the Central Mediterranean and Italy. Elsevier. Goes, S., D. Giardini, S. Jenny, C. Hollenstein, H.-G. Kahle, and A. Geiger (2004), A recent reorganization in the south-central Mediterranean , Earth Planet. Sci. Lett., 226, 335–345, doi:10.1016/j.epsl.2004.07.038 Govers, R., and Wortel, M.J.R., 2005, Lithosphere tearing at STEP faults: Reponse to edges of subduction zones : Earth and Planetary Science Letters, v. 236, p. 505-523. Gutscher, M.-A., Dominguez, S., Mercier de Lepinay, B., Pinheiro, L., Babonneau, N., Cattaneo, A., LeFaou, Y., Barreca, G., Micallef, A., Rovere, M., (2014). Deep crustal faults and the origin and long-term flank stability of Mt. Etna . ��� �������� ������� ������� ����� EGU Meeting, Vienna, Apr/May 2014. GNGTS 2014 S essione 1.2 133