GNGTS 2014 - Atti del 33° Convegno Nazionale

and shallow subsurface geology (e.g. Brogi and Liotta, 2006; Mirabella et al. , 2011). We used these data to build-up the shallow sections, to be incorporated in our geological models. Since the traces are spaced each other less than 20 km, we can assume that the deep (i.e. lower crust and upper mantle) structures are the same for the three sections: so we projected the available data on the three sections along the arcuate trace, depicted by both gravimetric and regional geological structures. Stratigraphy and density data. We used GM-SYS program to calculate the gravity response of the 2D geologic models. This program considers the method of Talwani et al. , (1959) and Talwani and Heirtzler (1964) and makes use of the algorithm described in Won and Bevis, (1987). The curvature of the Earth was not considered because of the short length of the profile. The model extends more than the real length of the section to eliminate edge effects. We dedicated a strong effort in selection of the density data following this path: - definition of the stratigraphic model (i.e. definition of the main litho-mechanical layers within the sedimentary cover and the upper crust); - collection of density data from the literature for each of the layers of the model, as well as for the lower crust and for the mantle; - calculation of a new data-set of density data, derived from the velocity data collected by active seismic surveys; - integration of stratigraphic, literature and new data in a comprehensive model. Our stratigraphic model can be schematically divided into two sections: a) sedimentary cover and upper crust basement; and b) lower crust and upper mantle. Sedimentary cover and basement. The shallow part of our models is characterized by a great lateral and vertical variability, comprising a large number of different geological units. For our purposes, we grouped these rock bodies in a limited number of representative lithological units, briefly described in the following. Pliocene-Pleistocene Units include continental and shallow marine sediments deposited in both hinterland and foreland recent basins. Liguride Units include a complex assemblage of sandstone, marls, limestones and ophiolites (Cretaceous- Miocene). Tuscan turbidites include Macigno Sandstones and the lithologically complex Scaglia Toscana fm (Cretaceous-Early Miocene). Umbrian turbidites include Marnoso-Arenacea and the other flysch-like successions exposed in the Umbria and Marche region (Early to Late Miocene). Carbonate Units include the marine Mesozoic-Early Tertiary multilayers of both Tuscan and Umbria-Marche successions. Evaporite Units include alternated anhydrites and dolomites (Burano fm.) and the overlaying marls of Raetavicula contorta Fm., in both Tuscan and Umbri-Marche realms (Late Triassic). Basement s.l. units include both terrigenous (Verrucano) and meta-sedimentary (mainly phyllites) rocks of the shallower part of the basement (Late Paleozoic-Early Triassic). Upper crust corresponds to the crystalline basement. Lower crust and upper mantle. Many seismic refraction studies investigated crustal structure of Northern Apennine and adjacent region. The results where synthesised on Moho isobath maps (e.g. Scarascia et al. , 1994; Scrocca et al. , 2003). They highlight the presence of a thin Tyrrhenian crust (20-25 km), contrasting a thicker Adriatic crust (30-35 km), separated by a sharp Moho step. In this work we analyzed the crustal models that present different estimation of Moho depth accross the studied regional transect (Ponziani et al. , 1995; Piana Agostinetti et al. , 2002; Mele and Sandvol, 2003). Ponziani et al. (1995) reconstruct a detailed velocity model for the P waves for the crust and the mantle, considering an attenuated velocity for the Tuscan Moho in the Tyrrhenian Domain (7.7 km/s) and a velocity of 8.0 km/s for the Moho in Adriatic Domain. They propose also a 152 GNGTS 2014 S essione 3.2