GNGTS 2016 - Atti del 35° Convegno Nazionale

62 GNGTS 2016 S essione A matrice 3. ��� �������������� ������� ������� ������ ��������� ���� �������� ������� ����� n.1 bi-dimensional passive seismic arrays processed with Extended Spatial Auto- Correlation (ESAC) (Ohori, 2002; Okada, 2003; Parolai et al. , 2006); 4. �� � ������ ������� ������ ������������� �������� �� ������� ������ ����� ����� n. 1 active seismic arrays (Multistation Analysis of Surface Waves, MASW) (Park et al. , 1999); 5. ���������� ���������� �� �������������� �� ���� ���� ������ �� ������� ��� ������ ��� ��� foreshocks recordings by accelerometers in four site (three in Pescara del Tronto and one in Vezzano). Fig. 2 – Sketch map of the survey area with location of the geophysical surveys. Below, some results coming from geophysical surveys were summarized. Fig. 3 shows the ERT carried out in Pescara del Tronto. The electrical image shows a relatively low resistivity range, from 10 to over 320 Ωm, and a resistivity pattern characterised by relatively strong lateral and vertical gradients. The shallow relatively high resistivity layer could be associated to slope deposits (pelitic-arenaceous lithofacies-LAG1e), overlying the substratum constituted by the Laga Formation (arenaceous-pelitic lithofacies - LAG1b), according to the geological map of the area (Marche Region Geological Maps at http://www.ambiente.marche.it) . The Vs velocity profile estimated by ESAC analysis shows two impendence contrasts at about 10 m (V S from 300 to 600 m/s), probably due to the discontinuity between slope deposits and the underlying Laga Formation, and at about 30 m (V S from 600 to 1000 m/s), probably due to the different lithostratigrafic members, from pelitic to arenaceous, in the frame of the Laga Formation. All sites reveal amplification in frequency range between 3-7 Hz (range of interest of built environmental). The preliminary Horizontal-to-Vertical Spectral Ratio (HVSR) functions using 80 earthquakes with 2.4 ≤ M L ≤ 4.3 in AS1, 60 earthquakes with 1.2 ≤ M L ≤ 3.3 in AS2 and 88 with 2.5 ≤ M L ≤ 3.9 in Vezzano site (Fig. 3) show that the rocky site in Vezzano shows flat amplification function, whereas Pescara del Tronto evidences a significant amplification variability. Although both stations in Pescara del Tronto are located on the same geological formation (Laga Formation), they show different amplification functions: AS1 site has a clear