GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 2.2 365 waves (Bonnefoy-Claudet et al. , 2006). The wavefield is a combination of both types and the shape of the HVSR curve provides information about the shear wave velocity profile in shallow sediments (Galea et al. , 2014). Polarization analysis was introduced by Vidale (1986) and implemented by Burjánek et al. (2010) by adopting a continuous wavelet transform (CWT). The particle motion is characterized at given time and frequency by a 3D ellipse. The WAVEPOL package outputs the analysis of ambient noise time-series in visual representations of combined angular and frequency dependence. The ellipticity of the particle motion is defined as the ratio of the semi-minor axis to the semi-major axis of the ellipse (i.e. 1 represents circular particle motion and 0 purely linear motion), pointing out the polarization effects. It is represented as a 3D histogram of ellipticity versus frequency. Histograms of strike of the ellipse major axis are represented as circles on a polar plot, in which the frequency increases along the radius, and a colour ramp is used to denote amplitude in each histogram. Results. HVSR analysis. The noise analyses pointed out a marked difference in the seismic response between the unstable areas and the stable plateau zone (Fig. 2). The HVSR curves show significant resonance peaks at frequency higher than 5.0 Hz in the measurements carried Fig. 2 – Orthophoto of the Cala Rossa western sector showing: open and estimated fractures, the 47 noise measurement stations and HVSR curves grouped by different areas; for the unstable area (in the yellow frame) only the most significant HVSR curves are shown.