GNGTS 2015 - Atti del 34° Convegno Nazionale

The hills of the province of Trieste are part of the chain of External Dinarides, in particular the west sector chain of Idria Rift. The area is characterized by two main structural reasons. The dominant factor of the tectonic landscape is the Karst Thrust that develops in a Dinaric featuring basically all the Trieste area. The other important is some smaller thrusts that affect extensively the area of Flysch on which stands the city of Trieste and then extend to the base of the coastal slope and within the Gulf (Busetti et al. , 2010). The system represents the most external Dinaric thrusts. It is characterized by intense deformation, in particular within the Eocene Flysch sequences, and it is affected by tectonic activity lasting to the Plio-Quaternary. Some sub-vertical faults with an anti-Dinaric NE–SW orientation and a strike-slip activity, cut the previous overthrusts (Carulli, 2011). The outcrop of Flysh present in the study area, in the southern slope of Mount San Pantaleone, is characterized by a noticeable isoclinal fold, typical of this lithology, which are found in sections throughout the area dominated by the presence of main thrust. The evolution of the morphology of the land is undoubtedly linked to the interventions of the man who, in order to land use, amended the original morphological detail. The previous location of industrial plants has redesigned over the years the current appearance of the slope. The current shoreline, south of the study area, is not of natural origin but was generated by the contribution of debris, inert waste and ash landfill of the local dump (Via Errera), who moved the shore line of 150 m by adjusting the trends of natural coast. Along the paleo shoreline there are some outcrops of marine clays mixed with bitumen (anthropogenic) and with the presence of fragments of remains white shells. Looking at the LIDAR topographic data, it is observed that the Mount San Pantaleone has a share of 40-50 m and its southern side has an average slope of 40°. The shape, probably affected by the dominant human activity, is similar to the forms of coastal shelf and slope, with a cliff at times sub-vertical. Field investigation. As part of the geophysical survey, in view of the peculiar characteristics of the site under study, they were applied both methods of electrical resistivity tomography and the refraction seismic. Electrical Resistivity Tomography (ERT). ERT is a commonly used geophysical method for the imaging of shallow sub-surface target. The equipment used is called “light 4Point hp” and is produced by L-Gm Lippmann Geophysikalische Messgeräte (Germany). The location of the electrodes was preceded by a topographic survey to define the alignment and the distance between electrodes. During the prospecting it was adopted configuration Wenner-Schlumberger with the technique of direct measurement and another to estimate the error of the measurement. The ERT survey was divided into 9 lines, with 550 channels, distance between channels 1 to 4 m and a total length of 1,090 m. Refraction seismics. The acquisition of the seismic data was performed with the recording system Summit - DMT, consisting of a USB interface connected to the PC and from units of A / D conversion arranged on the ground, connected to the individual vertical geophones to 10 Hz. It was used an accelerated mass seismic source called PWD (Power assisted Weigth Drop). This system of energization is made from a steel beam that is accelerated by an elastic strap, tensioning through the hydraulic lift of a piston integral with the mass itself, to increase the speed and generate a seismic signal more impulsive energy. The source is installed on a truck Scam 4WD. The acquisition parameters are 5 refraction lines, 550 channels, 112 shots, 2 m distance between stations, 0.250 ms sampling, 2 s record length, 1090 m total length. Much of the seismic lines were acquired at the ERT locations. Surface wave . Surface wave methods allow the extraction, and then inversion, of Rayleigh/ Love wave dispersion properties to recover shear-wave velocity profile. In general, the model GNGTS 2015 S essione 3.2 71