GNGTS 2017 - 36° Convegno Nazionale

560 GNGTS 2017 S essione 3.1 Li, Y., Braitenberg, C., &Yang, Y. (2013). Interpretation of gravity data by the continuous wavelet transform: The case of the Chad lineament (North-Central Africa). Journal of Applied Geophysics, 90, 62-70. Louis, P., 1970. Contribution géophysique ä la connaissance géologique du basin du Lac Tchad. Paris, ORSTOM. Mem., 42: 311 p.p. Liégeois,J.P.,Abdelsalam,M.G.,Ennih,N.,&Ouabadi,A.(2013).Metacraton:nature,genesisandbehavior. Gondwana Research, 23(1), 220-237. Schuster, M., Duringer, Ph., Ghienne, J.-F., Vignaud, P., Mackaye, H.T., Likius, A., Brunet, M., 2006. The age of the Sahara Desert. Science 311, 821. DEEP SEISMIC PROSPECTING: IMAGES FROM CENTRAL SICILY R. Nicolich, M. Giustiniani, U. Tinivella Istituto nazionale di Oceanografia e di Geofisica Sperimentale – OGS, Sgonico (TS), Italy Introduction. The seismic transect SIRIPRO, long about 100 km, was acquired in 2007 starting from Termini Imerese, in the north, to Gela at southern coast, crossing Maghrebian belt and Caltanissetta through the slope of Hyblean and Pelagian platform facing southern Sicily. It allowed exploring structures of Central Sicily illuminating the foreland crust and the large- scale Neogene overthrust of the Maghrebian Chain. An exhaustive analysis of the profile let us depict important targets: a) Caltanissetta crustal scale syncline developed between foreland and hinterland of the Maghrebian Chain with the accumulation of allochthonous terrains; b) nature of the foreland crust and its northwards thinning; c) collisional mechanism up to recent uplifts and northwest-southeast compressions even though with slow movements; d) development of the frontal shape of the fold&thrust belt constrained by the inhomogeneity of the foreland plate; e) southward pushes of Tyrrhenian deep crust and mantle. Newly processed data (after Accaino et al. , 2011) improved signal/noise ratio extracting information previously hidden by approximate static corrections and source generated noise. To relocate shots and receivers at a given datum plane, usual assumption of a vertical near- surface ray-path, when static corrections are applied, looks inadequate for acquisitions wit long offsets and significant laterally varying velocities, obstacles that did not favour penetration and energy focusing. The choice of a group spacing of 50 m and shots intervals of 250 m, obligatory detecting reflected energy from deeper interfaces, ignored potential complex near- surface structures while crossing a fold&thrust belt. The coverage took advantage of the large number (240) of active channels, but the near surface information remained poor or absent. To increase energy penetration, signal recovery and more reliable migration process more shots/ km should have been adopted. To remove missteps from rapid variations of the near surface velocity, complex methods, such as Wave Equation Datuming (WED), should be used. Likewise, we applied WED to remove source generated noise, increase resolution and signal/noise ratio, which is a correct and appropriate procedure to improve deep crustal reflections (i.e., Barison et al. , 2011; Giustiniani et al ., 2015 ) . New processing of SIRIPRO seismic profile. Considering the length of the seismic profile (about 100 km), we divided it into two parts, labelled PN (northern part) and PS (southern part) from here on, to easily manage a huge amount of data during processing, especially for WED application. We also limited listening time to first 12 s to reduce computation times. In fact, WED demands heavy computations requiring long-lasting times. Anyway, a limitation to 12 s allowed us to have an image of a whole crust on section PS, whereas the structures of the deep crust and its involvement in the chain building was our main interest on PN section. We utilized parallel computing facilities at CINECA (www.cineca.it ) centre.