GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.1 7 al. , 2012), and subsequently it has been continued into the Messina Strait. This fault system, however, still lacks a convincing documentation. Detailed morphobathymetry shows no surface expression, and in its southernmost strecth, the morphology clearly displays a left-lateral motion (Gutscher et al. , 2017). Seismic profiles show features that can represent the deformation within the accretionary wedge, without the need to have a lithospheric tear. 2.3. Issues related to lithospheric tears - Lower plate Quaternary rifting below the Calabrian accretionary wedge. A ca. 50 km-wide belt of transtension is inferred to be present between the Alfeo and Ionian Faults (Fig. 1; Polonia et al. , 2017). This transtension is considered to be responsible for a crustal thinning from 35 to 20 km (beta factor 1.75). A Pleistocene extension of that amount, comparable to the stretching in the North Sea Central Graben but achieved in a shorter time interval, would have left a clear trace in the upper crustal section, and this is not the case. Recent refraction data have been acquired in the western Ionian Sea (Dellong et al. , 2018). A crustal profile crossing the Malta Escarpment and continuing NE-ward, off the coast of Calabria, shows a crustal thinning between the Malta Escarpment and Calabria. According to the authors this refraction data support that the Alfeo Fault acted as a lithospheric tear, along which a sedimentary basin formed by rifting during the Plio-Pleistocene. In both these interpretations emphasis is given to the role of sub-vertical strike-slip faults, whereas the role of displacement of the Calabrian Arc along the subduction interface is possibly underestimated. 2.4. Seismicity and tsunamigenic potential of lithospheric tears. The northern stretch of the Ionian Fault is interpreted to be responsible of the 1908 Messina earthquake and tsunami (Polonia et al. , 2012). The NW-strike of the Ionian Fault, however, is not compatible with the seismological data of the 1908 earthquake. Moreover, there is no evidence of such a fault in the seismic data acquired in the Messina Strait (Argnani et al. , 2009). The 1169 earthquake and the1693 eastern Sicily earthquake and tsunami have also been related to a lithospheric tear, the Alfeo Fault (Polonia et al. , 2012). The strike slip motion of this fault, and its subdued morphology suggest that its tsunamigenic potential is limited. Even assuming a vertical throw, a large magnitude is required in order to reproduce the 1693 tsunami, and ist effect would be felt along the Calabrian coast (Armigliato, 2018; p.c.); but there is no mention of such an event in the chronicles. So far the most promising tectonic structure that can explain the 1693 earthquake and tsunami is the fault located offshore Augusta (Argnani et al. , 2012), whether or not it is related to a lithospheric tear. References Argnani, A.; 2005: Possible record of a Triassic ocean in the southern Apennines. Boll. Soc. Geol. It., 124, 109–121. Argnani, A.; 2009: Evolution of the southern 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.), the Geological Society, London, Special Publications, 311, pp. 193–212. Argnani. A.; 2014: Comment on the article “Propagation of a lithospheric tear fault (STEP) through the western boundary of the Calabrian accretionary wedge offshore eastern Sicily (Southern Italy)” by Gallais et al., 2013 Tectonophysics. Tectonoph. 610, 195–199. Argnani, A. and Bonazzi, C.; 2005: Tectonics of Eastern Sicily offshore. Tectonics 24. http://dx.doi. org/10.1029/2004TC001656 TC4009 Argnani, A., Armigliato, A., Pagnoni, G., Zaniboni, F., Tinti, S. and Bonazzi, C.; 2012: Active tectonics along the submarine slope of south-eastern Sicily and the source of the 11 January 1693 earthquake and tsunami. Nat. Hazards Earth Syst. Sci. 12, 1311–1319. Argnani, A., Mazzarini, F., Bonazzi, C., Bisson, M. and Isola, I.; 2013: The deformation offshore of Mount Etna as imaged by multichannel seismic reflection profiles. J. Volcanol. Geotherm. Res. 251, 50–64. Argnani A., Cimini, G.B., Frugoni, F., Monna, S. and Montuori, C.; 2016: The role of continental margins in the final stages of arc formation: Constraints from teleseismic tomography of the Gibraltar and Calabrian Arc (Western Mediterranean). Tectonoph. 677, 135-152. Breen N.A., Silver E.A. and Hussong D.M.; 1986: Structural styles of an accretionary wedge soutj of the island of Sumba, Indonesia, revealed by SeaMARC II side scan sonar. Geol Soc. Am. Bull, 97, 1250-1261.