GNGTS 2019 - Atti del 38° Convegno Nazionale

284 GNGTS 2019 S essione 2.1 Preliminary results and discussion. PSD, PDFs plots and others statistical parameters have been obtained. For each station, the PSD and the relative PDFs have been calculated. The Fig.1 represents a good example of PDFs plot, computed for the vertical component of a station (FAGN). This is a probabilistic representation of the spectra overlap. PDFs was performed also for the horizontal components. For example, in this station the low noise values fall within the range of Peterson (1993) reference model (black lines). There seems to be a stable noise, presenting an intermediate dispersion value (about 30 dB). After extracting all the PDFs of each stations, these have been plotted into a single graph (Fig.2a). The red lines represent the mean value: it is possible to observe some noisy stations for low and high frequencies, maybe due to sensor calibration or the presence of earthquake sequences. The dotted yellow line indicates the average of all the average of PSD. In the figure on the right (Fig.2b) the corresponding overplot of the average of all PDFs is shown. This is a PDFs representative of all the stations analysed (vertical component) and could be considered as a new reference noise for Italian territory. A first statistical analysis was made to understand the statistical properties of the noise, especially the noise power distribution in the four frequency bands indicated above. Histograms have been computed for each band and for the horizontal and vertical components and Horizon to Vertical ratio. In addition, a spatial-statistical analysis was performed. For example, Fig. Fig. 1 - PDF for the vertical component of FAGN station. Fig. 2 - a) overplot of the average PSD and b) overplot of the average PDF determined for the vertical components of the 233 analysed stations.