GNGTS 2015 - Atti del 34° Convegno Nazionale

the bedrock. To more effectively support this project new bathymetry, geological/geotechnical and geophysical data were collected. Geological setting. The Gulf of Trieste, the northernmost sector of the Adriatic Sea, is part of the Adriatic Apulian foreland. It is composed of the Mesozoic Adriatic Carbonate Platform (Vlahović et al. , 2005), Paleocene-Eocene carbonates and Eocene Flysch (Onofri, 1982), a turbiditic sequence composed by an alternation of sandstones, siltstones and marlstones. From a structural point of view, two main patterns interest the Trieste Karst area: the Karst Thrust, developed in Dinaric direction (NW-SE), which forces limestones to overlie the Flysch of Trieste, and some minor thrusts in the turbidites. The Gulf of Trieste was extensively recently explored by several offshore seismic lines (Busetti et al. , 2010, 2012) that allow to obtain new information to refine previous geological/structural model (Cavallin et al. , 1978; Carulli et al. , 1980; Carobene et al. , 1981). The Trieste Marine Terminal (TMT) is located in the southern part of the Trieste harbour. Several seismic acquisition were carried in this area. In the 1950s, a single channel reflection seismic (Mosetti and Morelli, 1968) provided information about the Quaternary sediments covering a drainage pattern superimposed on the Eocene Flysch that during the Messinian were emerged favouring the fluvial erosion (Fantoni et al. , 2002). This was the first marine geophysical experiment in Italy followed by two refraction profiles (Finetti, 1965, 1967) and, recently, by some single channel reflection seismic campaigns acquired for geotechnical and environmental studies (unpublished data). In the studied area the bedrock is represented by the Flysch formation covered by Plio- quaternary sediments (Brambati and Catani, 1988; Masoli and Zucchi, 1968). The bedrock is characterized by an alternation of layer of different geomechanical behaviour and by the presence of a weathered zone. The sedimentary sequence covering the Flysch is characterized by an alternation of levels of silt/sandy clay (greenish gray) with fragments of shells and layers of sand fine to medium, and trace of gravel. Silt/sandy clay are saturated with a very soft consistency and sand has a very loose apparent density. Field investigations. The study area is located on the front of the TMT (about 200,000 m 2 ) with an average water depth of 20 m (Fig. 1). The marine bathymetric and geophysical survey was carried out in the Autumn 2014 by the OGS boat “Anthea” equipped for shallow water offshore survey. Underwater refraction seismic requires also the onshore access to the pier to record the hydrophone array data. Data were collected in two phases because of the presence of strong Bora wind that inhibits any offshore activities. In the first part were collected bathymetric, side-scan-sonar, magnetometer and sub bottom profile data, in the second the refraction data. As the front of the TMT is characterized by an intensive maritime traffic, the acquisition phase required a strong coordination with the local maritime authority and the several operators involved in the different harbour activities (berthing/unberthing, loading/unloading , etc.) Navigation and tidal stage. Navigation data for water-based survey were collected with a Trimble DGPS DSM232 in WGS84 and were passed to the different acquisition tools and the navigational software at a rate of 1 Hz. PDS2000 software with coast line and infrastructure perimeters was used to display the course of the boat and allow real-time navigation along the theoretical predetermined lines. Tidal stage for data elevation correction were obtained from Trieste Station, belonging to the National Tidegauge Network of “Istituto Superiore per la Protezione e la Ricerca Ambientale – Ispra”. The station is located in Trieste’s seaport, near the “Lega Navale” wharf. The tidegauge station is equipped with altimetric datum. Each datum is referred to the average sea level, measured in Genoa using the ancient Thompson tidegauge. The datums are metallic check tags, used to determinate the altimetric level by means of high precision leveling, following the guidelines fixed by IGM (Italian Military Geographic Institute). From 07/10/2009 the “hydrometric level” is measured with a new high precision radar sensor SIAP+MICROS TLR. 64 GNGTS 2015 S essione 3.2