Influence of soil parameter uncertainties on site ambient noise horizontal to vertical spectral ratio modeling

The noise horizontal-to-vertical spectral ratio (NHV) has been applied for inverting subsurface velocity structures, but the non-uniqueness issue in the inversion remains prominent. Parameter sensitivity analysis is crucial for understanding the extent to which parameters influence inversion results, providing reasonable value ranges for each parameter, and offering rational constraints to mitigate the non-uniqueness of solutions. This study takes 636 sites from the KiK-net network as benchmark sites and employs the Monte Carlo method based on Toro's statistical model to generate 200 random samples for each site's shear wave velocity (V_S), compressional wave velocity (V_P), layer thickness (h), and density (ρ) parameters. These random samples are then combined into six scenarios, serving as the stochastic site models for uncertainty analysis. Finally, based on the diffuse field assumption (DFA) for NHV forward modeling, the NHVs and their standard deviations are calculated for each scenario. The standard deviations of NHV are further utilized to conduct a sensitivity analysis of soil layer parameter uncertainties' impact on NHV. The results indicate: 1) The NHV peak frequency (f_peak) is most sensitive to the V_S and h combination, followed by the V_S and ρ combination. Among single-parameter scenarios, f_peak is most sensitive to V_S, followed by h, and relatively insensitive to V_P and ρ. 2) The NHV peak amplitude (A_peak) is most sensitive to the V_S and ρ combination, followed by the V_S and h combination. Among single-parameter scenarios, A_peak is most sensitive to V_S, approaching the sensitivity level of the V_S and h combination, followed by ρ, and relatively insensitive to h and V_P. 3) Within the 0.1–50 Hz frequency band, the NHV curve is most sensitive to the V_S and h combination, followed by the V_S and ρ combination, and the single-parameter V_S scenario. Among single-parameter scenarios, the NHV curve is secondly sensitive to h, while its sensitivity to V_P and ρ is relatively low. The sensitivity patterns of NHV to soil parameters revealed in this study are widely applicable, providing effective constraints for NHV inversion, assisting in optimizing parameter combinations, assessing the feasibility of inversion schemes and the credibility of results, and offering beneficial insights for improving the efficiency of the inversion process.