GNGTS 2013 - Atti del 32° Convegno Nazionale

The deep exploration of the ma- rine areas started in 1988 in the Pro- venzal Basin (again a CROP-ECORS joint venture) and after covered all the Italian neighbouring seas with CROP and with similar projects (ETNASEIS, SINBUS, PROFILES, IMERSE, ...). The dynamite source was em- ployed in several transects, but also heavy vibrators were used, for ex. in the narrow mountain valleys, but still adding explosive shots to aid imaging the deepest reflecting markers. The depth penetration of vibroseis signals is turned up to be particularly low in such areas where high-impedance rocks are exposed at the surface. The use of comple- mentary wide-angle acquisitions continued about everywhere with in-line profiling or with fans or again designing cross-lines to enable 3D images extracted from a wide corridor centred on the main profile. The operative parameters employed in the acquisition were modified with the continuous improvements of the recording technologies and the gained experiences, varying the number of the active recording channels, the group intervals, the offsets; all parameters choice limited by the available funding. The addition of the gravity information with the Bouguer anomalies can help to position the deep basins, the deep roots of the orogenies and of the high density bodies at shallow depths. Both the seismic and gravity interpretation take mutual advantage by iterative use of the two data sets and of the constraints posed to fulfill both observed data. The gravity field can be used to extend the interpretative models beyond the seismic profile and 3D gravity models have been presented to control the laterally variable crustal architecture. In Fig. 1 an example of a gravimetric model, which utilized the seismic information along a sector of the EGT transect from the internal crystalline massif in Switzerland to the Ligurian Sea, crossing the Milano belt, the western Po plain and the northern Apennine arc. The structural setting of the Adria domain results from the convergence of the plate margins producing a foreland-foredeep domain consumed by the advancing neighbouring chains with vertical offset of respective Moho’s. In Fig. 2 an example of wide-angle fan profiling, which were of primary importance for the interpretation of the deep interfaces disclosed in the reflection seismic sections of the CROP- ECORS project (Damotte et al. , 1990), revealing a dramatic imbrication of the upper mantle and crust. Organizing the sampling interval of reflectors along the cross sections and the shot- receivers distance in fan to have reflecting points around the critical distance corresponding to the common depth point of the near vertical reflection profile, the wavelet from the base of the crust is known to be very energetic and can be identified by the maximum amplitude signal. The root zone of the chain was outlined down to 55 km depth with the flaking of the lithosphere under the chain in the Briançonnais zone, while the hinterland Moho is raising stepwise from the Po plain up to about 13 km depth, the base of the outcropping rise known as the Ivrea lower crust body. Fig. 1 – The gravimetric model (from Marson et al. , 1994) along the European GeoTraverse, crossing the Alps, the Po Plain and the Apennines, down to the Ligurian Sea. The model settles the European Moho at 60 km or more beneath the Po Plain with Adria Moho down-bended to about 40 km by the Apennines overthrust, Apennines here characterized by a vertical Moho uplift. Density values in gr/cm 3 . XIV GNGTS 2013 L ectio M agistralis