Ambient noise horizontal-to-vertical spectral ratio in site effects estimation and correlation with seismic damage distribution in urban environment: the case of the city of Thessaloniki (Northern Greece)

The validity of the estimation of seismic site response characteristics from ambient noise measurements was investigated in the downtown district of the city of Thessaloniki (Northern Greece), which was strongly affected by the 20/6/1978 (M=6.5) damaging earthquake. For this purpose 250 'single site' ambient noise measurements were performed in a dense grid of points covering the center of the city. The ambient noise H/V spectral ratio for each site was calculated and the fundamental frequency (fo) and corresponding H/V amplitude level (Ao) were estimated. Contour maps of both, fo and Ao, were compared with results from geological and geotechnical studies as well as with macroseismic data of the 1978 earthquake and were found to be well correlated. These comparisons provide strong evidence that ambient noise measurements properly processed with the (H/V) spectral ratio technique can be used as an inexpensive and fast tool for microzonation studies in urban environments.