GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 2.2 359 and the Spatial Autocorrelation (SPAC) are primarily considered. Capabilities and limitations associated to both of them are discussed considering the implication of spatial sampling for the specific array setup. The role of higher modes in active tests is also discussed. Criteria to assess the reliability of the experimental dispersion curve are established taking into account the role of lateral variability, higher modes and near field effects. The typical patterns of the experimental dispersion curve and implications on the interpretation of the available data are also discussed (see for example Fig. 1). Parameterization of the interpretation model is a crucial issue for the solution of the inverse problem aimed at the estimation of the shear wave velocity profile. In this respect, number of layers, a priori parameters and minimum and maximum resolvable depths are considered. The inverse problem can be resolved with deterministic local search methods or global search approaches. The latter should be preferred as they allow an explicit evaluation of the consequences of solution non-uniqueness by selecting a set of possible solutions, which honor equally well the experimental dataset (see Fig. 2). The guidelines end with a discussion on the use of surface wave surveys for earthquake engineering studies. In particular the estimation of V S,30 (i.e. the equivalent velocity for the top 30m below the ground surface) is often a primary target considering the diffuse use of this average site parameter as a proxy of site response in building codes and in the derivation of ground motion prediction equations (GMPEs) that are used to evaluate seismic hazard at a site. In this respect the following evidences are to be considered: 1) ��� � the V S,30 as calculated from the shear wave velocity profiles is quite accurate and precise, because it is practically not affected by solution non-uniqueness. Indeed the comparisons from literature data and from the InterPACIFIC project show that the estimate is very close to the one obtained with invasive tests and the uncertainties are quite small (see Fig. 3); Fig. 2 - Example of global search method result. a) In red the profile with minimum misfit value. The green dashed lines represent the boundaries of the search area. The profiles, from blue to yellow according to their misfit values, are all the accepted profiles; b) in red experimental data and the line from blue to yellow correspond to the forward response of the accepted profiles; c) comparison between experimental data (in red) and the forward response of the profile with minimum misfit value (in blue) (Mirandola site, InterPACIFIC project; Foti et al ., 2017).