GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 2.2 241 Civitavecchia, La Spezia, Palermo, Ponza and Venezia were taken in account. The results of this analysis enlighten the presence of a statistically significant correlation between sea-wave activity and HVSR peaks amplitude in the low frequency range (0.25-0.3 Hz); specifically, the maximum correlation coefficient values (about 0.5-0.6) are verified with Tyrrhenian sea data (La Spezia and Cagliari) and with the nearest station (Ancona and Venezia) to the study area (Tab. 1). As concerns the main peaks in the range 0.8-1.3 Hz, no significant correlation was found with global or local meteorological conditions. Whether such fluctuations may depend on short scale variations of the impedance contrast or on local sources of ambient vibration related to the anthropic activity remains an open question. Fig. 2 – Localizations of the 4 macrozones identified examining all HVSR curves. In green are represented zone 1 borders, in purple zone 2 borders, in red and in blue, respectively, zone 3 and zone 4 borders. Black bars show main peak frequency interval, light gray bars indicate secondary peak frequency interval. Tab. 1 - Values of the correlation coefficients obtained by comparing sea-wave heights measured in each of the seven stations belonging to “Rete Ondametrica Nazionale” and amplitudes of the low frequency range (A1) and of main peak (A0) obtained in the study area. Station name Correlation coefficient A1 Correlation coefficient A0 Ancona 0.55 0.1 Cagliari 0.58 0.17 Civitavecchia 0.25 0.24 La Spezia 0.60 0.16 Palermo 0.56 0.4 Ponza 0.44 0.09 Venezia 0.49 0.08