EFFECTS AND MICROZONATION IN THE CITY OF THESSALONIKI (GREECE) - COMPARISON OF DIFFERENT APPROACHES

Ten seismological stations were installed for 3 months in the city of Thessaloniki (Greece) to record earthquakes and ambient noise over are as of different geotechnical characteristics. About 40 local earthquak es were recorded with a good signal-to-noise ratio, in more than two s tations, We analyze the records with three different techniques: (a) t he classical spectral ratios to a reference station, (b) the receiver functions, and (c) the horizontal-to-vertical (H/V) spectral ratios on noise recordings, The results are compared in terms of predominant fr equencies and amplification levels, The three methods are found equall y able to reveal the fundamental frequency, Regarding local site ampli fication, they provide significantly different results with a general trend of the two H/V ratio methods (b and c) to underestimate the ampl ification levels compared to that inferred From the classical spectral ratio technique (a), The results are then used in relation with the m icrozonation of the city of Thessaloniki, A good correlation is found between the local site amplification and the type and age of the local geological formation as well as with the depth of bedrock, Finally, w e compare our observations with the damage distribution In the city, w hich was hit by a magnitude 6.5 earthquake in 1978. The amplification levels from spectral ratios obtained at each site exhibit a good agree ment with the map of damage intensity.