Constraints for the Vs profiles from engineering-geological qualitative characterization of shallow subsoil in seismic microzonation studies

A statistical analysis has been performed aiming at determining to what extent a qualitative engineering-geological characterization of subsoil may provide constraints to the shear wave velocity (Vs) profile. For this purpose, a large database of experimental values provided by seismic microzonation studies carried out in the last 10 years in Italy has been considered. This analysis suggests that statistical constraints can be provided to Vs values as a function of depth by considering main lithological characteristics of cover terrains and geological bedrock. The effectiveness and unbiasedness of resulting relationships are tested against some experimental situations. This information can be used to feed stochastic numerical simulations aiming at preliminary assessment of probability distribution of the expected seismic response in wide areas where an experimental geophysical/geotechnical characterization of the local subsoil is scarce or unavailable.