GNGTS 2013 - Atti del 32° Convegno Nazionale

all the measuring points (except P7) two recordings were carried out. The curves P1b, P6a and P6b exhibit a clear peak about 7.5-8.5 Hz that is due to stratigraphic resonance phenomena. P1a- P1b, P5a-P5b and P7 show a peak around 1.5-2.5 Hz probably due to a variation of impedance contrast. Instead the surveys performed in P2a-P2b and P3a-P3b reveal flat curves that do not identify any clear impedance contrast. In the municipality of Sant’Antonino di Susa the surveys were performed in four locations. In two of them (P1, P4) was carried out one survey more than the other. All HVSR identified a peak due to a high impedance contrast between two layers. In the measuring point P1a-P1b, P3 and P4a-P4b the frequency detected is about 2-2.5 Hz, while in P2 the frequency is about 5 Hz. In the municipality of Torre Pellice the surveys were performed in four locations. For all the measuring points were performed two survey. P1a-P1b, P4a show a peak about 2.5-3.5 Hz due to stratigraphic resonance phenomena. P2a and P3b reveal flat curves that do not identify any clear impedance contrast. P2b and P3a show a peak probably due to electromagnetic or human activities. P4b curve has an irregular trend that no allows to define a unique frequency. Fig. 1 shows all the HVSR curves. All the data (pre-existing and new investigations) allow to construct the litho-technical maps and the relative cross-sections, showing the different deposits outcropping the geophysical bedrock, defined as a level with V S of 800 m/s. Using the litho-technical maps and the relative cross-sections, the MOPS, for the 4 studied municipalities were produced. All the MOPS (Fig. 2) are characterized by different areas: 1 is classified as stable zone for the presence of the geologic bedrock, the other zone are classified as stable but with amplification effects due to presence of deposits. In-line HVSR measurements. The microtremor measures made in the previous municipalities and their pre-existing data allow us to define the areas with different seismic Fig. 2 – MOPS example. The figure shows the different area of Sant’Antonino di Susa and the HVSR in line survey location. 483 GNGTS 2013 S essione 2.3