This study presents the results of 90 seismic ambient noise measurementsin Palermo, the main city of Sicily (Italy). The dataset has been processed usingthe horizontal-to-vertical spectral ratio (HVNSR) technique and interpreted in terms oflocal geology, which is characterized by the presence of alluvial sediments of tworiverbeds masked by urbanization since the seventeenth century. HVNSRs show significantvariations in the study area: when the transition stiff to soft is crossed, a typicalspectral peak appears in the HVNSRs, mostly in the frequency band 1–2 Hz, and exceedinga factor of 3 in amplitude. Using available information on subsurface geologicalstructure, we compute theoretical 1D and 2D transfer functions. The resonancefrequencies of soft soils obtained by HVNSR are well reproduced by the fundamentalfrequencies from numerical modeling.The distribution of frequency peaks of HVNSR and their amplitudes are alsocompared with the local damage caused by historical earthquakes. Previous studiesdemonstrated that damage variations in Palermo were controlled more by near-surfacegeology than building vulnerability. A uniform vulnerability is an ideal condition totest statistical methods and their capability in seeking correlation between HVNSR andpotential damage due to local geological conditions. We apply two well-establishedmultivariate statistical methodologies (factor analysis and canonical correlation) to theHVNSR dataset and macroseismic data (damage grades of the European macroseismicscale). Through these analyses we quantify the significance of the correlation betweenthe HVNSR peak in the low-medium frequency range (0.5–3 Hz) and the occurrence ofthe highest damage grades. This approach allows us (1) to estimate the threshold valuein the resulting linear combination of the HVNSR amplitudes, which separates zonesof light damage from zones of significant damage, and therefore (2) to improve thespatial definition of potentially high hazard zones through a denser grid of microtremormeasurements.
|Numero di pagine||19|
|Rivista||Bulletin of the Seismological Society of America|
|Stato di pubblicazione||Published - 2008|
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