From HVSR to site SH response function: Potentiality and pitfalls inferred by 1D physical modelling

The capability of the ambient vibration Horizontal to Vertical Spectral Ratios (HVSR) in identifying the main aspects characterizing the conventional 1D site response curve was explored by physical modelling. This approach avoids possible biases induced by data processing by focusing on the underlying physical phenomenon. Moreover, differently from empirical approaches, this also allows exploring an unlimited range of subsoil configurations. By considering a huge set of realistic Vs profiles, HVSR curves were simulated and compared with the corresponding SH acceleration transfer functions (ATFs) obtained by linear equivalent numerical modelling, which is a standard for the professional practice. These comparisons focused on the values of F0 (the lowest resonance frequency), Fd (the frequency associated with maximum peak amplitude) and corresponding amplitudes (A0 and Ad respectively). Outcomes indicate that when F0 and Fd values coincide, frequency of the HVSR peak represents a reliable proxy to identify 1D resonance frequency. HVSR remains a good proxy for F0 in the remaining cases, while it is less effective concerning Fd in particular when this value is different from F0 and is identified in the frequency range 10-30 Hz. Finally, the results concerning peak amplitude values show a tendency by HVSR to underestimate in a similar way both A0 and Ad values.