A MICROTREMOR SURVEY IN THE AREA SHOCKED BY THE ML 5.2 SALO' EARTHQUAKE (NORTH ITALY): AN EMPIRICAL APPROACH TO DETERMINE THE EFFECTS OF GROUND MOTIONS Massa M. (1), Lovati S. (1), Di Giacomo D.(2), Marzorati S.(1), D’Alema E.(1) and Augliera P.(1) (1) Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, via Bassini 15, 20133 Milano, Italy. (2) GeoForschungsZentrum, Section 2.1 Earthquake Risk and Early Warning, 14473 Potsdam, Germany. Corresponding author:
[email protected] Abstract In this work the results of a quick microtremor survey performed in the municipalities situated in the epicentre area of the Ml 5.2 2004 Salò earthquake (North Italy) are presented. The aim of this study is to understand if the large amount of damage caused by the event (about 215 millions of euros only in the areas near to the epicenter) is correlated more to the local surface geology conditions or to the vulnerability of ancient Italian historical centers. A preliminary seismic zonation was carried out in 5 villages including about 30 measurements of microtremors analysed by the Nakamura technique (hereinafter HVNR). The points of measurement were carefully selected considering sites located both near damaged buildings and over different local geology conditions (alluvium deposits, fluvial-glacial deposits, debris fans and rock). In order to strengthen the HVNR results and to evaluate the reliability of the Nakamura analysis, a comparison with spectral ratios calculated on earthquakes (hereinafter HVSR) recorded at the strong motion station of Vobarno was made. In general, the outcomes of the survey highlight a possible correlation between local geology conditions and ground motion amplification for different frequency bands.