Assessment of the ground motion at reference rock sites in Italy
According to the code prescription, the reference ground motion is associated with those sites where rocks or stiff soils outcrop and the VS,30 value exceeds a given threshold. However, this condition does not ensure that the ground motion is unaffected by site-effects, as requested in several engineering application such as the evaluation of the site response using empirical approaches and numerical 1-D/2-D analyses. In these cases, the amplification function of the reference sites must be flat with amplitude equal to one over a frequency range of engineering interest (Steidl et al. 1996).
In the last years, we worked to develop the reference-rock detection method based on the identification of a set of site parameters that are related to geophysical and seismological data and to geomorphological and installation features. The main results of our studies are i) a selection of well-tested site parameters with a specific weight in the reference site identification; ii) a list of reference rock sites in Italy, with an associated score; iii) a model for the generic-to-reference rock corrective factor, parametrized in terms of VS,30 and κ0.