GNGTS 2015 - Atti del 34° Convegno Nazionale

the waves propagation is lost for the slope geometry (Fig. 1); the later arrivals on the right- part of the model (at higher elevation) show larger amplification rather than the left- part (at lower elevation). The synthetic signals have been used to compute the standard spectral ratio (SSR), choosing as reference site the first receiver (number #1 located at x progressive of 1000 m) situated on the left part of the model. The output signal at each receiver was decimated (downsampling at 100 Hz with an antialiasing filter) and processed by means of a discrete Fourier Transform after removing the mean. The Fourier amplitude spectra (FAS) were subjected to a smoothing arithmetic algorithm. Finally for homologous components, the ratio of the FAS of the signal at each receiver over the FAS of the reference receiver was computed. SSR for the x and z component is shown in Fig. 2 (left panel) indicating a complex pattern with alternate multitudes of amplification and deamplification branches. The maximum Fig. 2 – Left panel) SSR computed on synthetics for the half-circle, triangle and slope geometry. The plot refers to x component in case of S input polarization. The color scale is proportional to the SSR amplitude. Right panel) HVSR computed on synthetics for the half-circle, triangle and slope geometry. The color scale is proportional to the HVSR amplitude. HVSR was computed as (H/Href)/(V/Vref); see text. GNGTS 2015 S essione 2.2 89