A New Proposal for Site Classification Based on Ambient Vibration Measurements and the Kiknet Strong Motion Data Set

Abstract eng:
The goal of the present paper is to propose an alternative site classification and the associated spectral shapes, that could be easily used in building codes and microzonation studies. The site classification is based on a twoparameter characterization, consisting of the average shear wave velocity, VSz, over the top z meters (z between 5 and 30), and the site fundamental frequency f0. Both parameters are easily available from non-invasive survey techniques (ambient vibrations, MASW, SASW). A comprehensive analysis on about 500 sites from the KIKNET network, shows that f0 is very poorly correlated with any of the VSz values, thus providing independent, complementary information on the overall thickness and stiffness of sedimentary cover, and the surface stiffness. The corresponding site amplification factors are derived empirically from the average surface / downhole (SDSR) spectral ratios, with a correction procedure to normalize the raw SDSR to a standard reference (with VS30 = 800 m/s) located at surface. Finally, the correlation between site parameters and site amplification factors is achieved by normalizing the frequency axis with respect to f0, and a least-square fit of the amplitude with VSz. The largest variance reduction is obtained for the couple (VS30, f0), while a very simple site classification based only on f0 leads to satisfactory misfit values.

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