GNGTS 2015 - Atti del 34° Convegno Nazionale

higher modes were dominant. The MASW tests were performed using the two branches of the array separately. Tests were made using � ������ ������ �� � ��� ���� � ����� ������ �������� �� a hammer source of 8 kg, with a fixed offset distance of 10 m, recording five shots �� ������ ��� �������� ������������ ���� ����� ������� �� ��� ��������� to reduce the possible interference with other sources in the vicinity, with a registration length of 3 s ��� ������ ���� �� ��� ��� and sample rate of 512 Hz. In present study, the Rayleigh wave dispersion curves, obtained from the experimental setup, were inverted using the DINVER software (www.geopsy.org ) which provide a set of dispersion curve models compatible with the observed dispersion curve� ��������� �� ��� ������������ . �� ��� ������������ Inversion of the experimental dispersion curve needs a rough definition of the free parameters. This can be obtained using information coming either from a preliminary geological survey or from borehole data. If, as in our case, this information is not available, the values of parameters can be directly deduced from the fundamental mode of the Rayleigh wave dispersion curves (Albarello and Gargani, 2010). To invert the dispersion curve, a set of 1 to 8 uniform layers with homogeneous properties was considered, taking into account five parameters: shear waves velocity (V S ), thickness, compressional waves velocity (V P ), Poisson’s ratio and density (ρ). Results and discussions. Present study was focused on the part of the Salinelle area in which main activity is concentrated, as shown by the mud flow deposits. A dense microtremor measurement survey was carried out, selecting the recording sites in order to obtain detailed information on subsoil structure. For this reason, many of the measurements were performed on a linear deployment. The HVNR results set into evidence three different frequency ranges that appear interesting to get information on the subsoil structure. A low frequency peak at about 0.1 Hz was identified both on the Tr#1 and Tr#2, but with different amplitude (black arrows in Fig. 3a). Although, along the Tr#1 these peaks cannot be judged as particularly significant, we are incline to consider Fig. 2 – Examples of HVNR and directional resonance diagrams observed in the Salinelle area. 146 GNGTS 2015 S essione 1.3