GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.3 ______ ___ GNGTS 2023 “Much ado about nothing”: equivalence of numerical models for HVSR curves D. Albarello 1,2 , M. Herak 3 , E. Lunedei 1 , E. Paolucci 2 , A. Tanzini 1 1 Department of Physics, Earth and Environmental Sciences, University of Siena, Siena, Italy 2 Consiglio Nazionale delle Ricerche, Istituto di Geologia Ambientale e Geoingegneria, Rome, Italy 3 Department of Geophysics, Faculty of Science, University of Zagreb, Zagreb, Croatia The Use Of H/V Spectral Ratios (Hvsr) Of Ambient Vibrations To Constrain The Local Seismo-Stratigraphical Configuration Relies On Numerical Forward Models Able To Connect Observations With Subsoil Seismic Properties. Several Models Were Proposed To This Purpose In The Last Decades, Which Are Based On Different Assumptions About The Nature Of The Ambient Vibration Wavefield. Performances Of Nine Numerical Tools Implementing These Models Have Been Checked By Considering 1600 Realistic 1d Subsoil Configurations. Resultant Hvsr Curves Predicted By The Models Are Quite Similar Both In Their General Shape And In Predicting The Resonant Soil Frequencies, Possibly Because All Of Them Share The Same Basic Representation Of The Subsoil As A 1d Stack Of Flat Uniform Viscoelastic Layers. The Common Sensitivity To Transmission/Reflection Matrices Resulting From That Representation Explains The Well-Known Correspondence Of Hvsr Maxima To 1d Resonance Frequency Estimates, Regardless Of The Model Adopted For The Computation. This Also Suggests That Respective Different Representations Of Sources, Radiation, Seismic Phases Etc., Play Only A Minor Role When Only The Shape Of The Hvsr Curve Is Of Concern. On The Other Hand, Since Experimental Hvsr Curves Are Affected By Major Uncertainties (Due To The Lack Of Ergodicity Of The Ambient Vibration Stochastic Wavefield, Non-Ideal Experimental Settings, Non-Linearity Of Inversion Procedures, Etc.) Observations Cannot Be Used To Score The Relevant Models On Empirical Basis. It Is Argued That, For Practical Applications, Simpler Models Should Be Preferred To The More General Ones That Require Troublesome And Numerically Unstable Computations.