From HVSR to site response function: potentiality and pitfalls

The capability of the ambient vibration Horizontal to Vertical Spectral Ratios (HVSR) in capturing the main aspects of the seismic resonance phenomena was explored by numerical simulations. By considering a large set of Vs profiles, HVSR curves were simulated using two different models of the ambient vibration wavefield: the Diffuse Field Approach (DFA) and the Distributed Surface Sources (DSS) hypothesis. These curves were compared with acceleration transfer function (ATF) curves obtained by 1D linear equivalent numerical modelling of the considered seismo-stratigraphic profiles. In particular, comparisons focused on the values of F0 (the lowest resonance frequency), Fd (the frequency associated with maximum peak amplitude) and the corresponding amplitudes A0 and Ad. These comparisons show that HVSR curves deduced by both DSS and DFA models provide good estimates of F0, but are less effective as concerns Fd values. As concerns A0 and Ad, HVSR estimates show a systematic bias for both DSS and DFA models.