SEISMIC CHARACTERIZATION OF MAIN LITHOTYPES OUTCROPPING IN THE SIRACUSA URBAN AREA (ITALY)

This study aims to investigate on the dynamic properties of main lithotypes outcropping in the Siracusa urban area and to evaluate the features of the local seismic response. In the study area the substratum is represented by a Meso-Cenozoic carbonate sequence with interbedded volcanics. Non-invasive seismic prospecting techniques using the vertical component of surface waves (MASW and ReMi) were adopted, performing a total of eleven measurements. Ambient noise was recorded in twenty sites and the signals were processed through spectral ratio techniques. The experimental results show for the carbonate sequence a V(S30) of about 1000 m/s and, as expected for a rigid basement, the lack of dominant peaks in the H/V spectral ratios. Similar spectral features show the HVSR obtained from measurements performed on the Cretaceous volcanic which have V(s30)~ 600 m/s. Pronounced spectral peaks, at about 1.0 Hz, are observed in the HVNRs obtained from measurements performed in the southern part of the study area, where soft sandy sediments and alluvial deposits, having V(S30) in the range 300-400 m/s, outcrop.