## 5 Discussion  
This section provides an interpretation of the numerical results, with a particular focus on distinguishing the effects of shear wave velocity inversions from those caused by two-dimensional stratigraphic variability. It also serves as a basis for the quantification of the seismic risk to structures and evaluation of the seismic demand in terms of ground motion. The TFs shown in Figure 6 reveal different trends for the 1D and 2D models. In general, 1D analyses amplify peaks at higher frequencies. This effect is influenced by the magnitude of the soil D, the method by which D is implemented in the numerical code, and the level of shear deformation induced in the soil during an earthquake. For sites exhibiting velocity inversion (S3H, S1H, and S1U), 1D models yield slightly lower values (f\({}_{0}\)) than those provided by the 2D analyses. Notably, only the 2D analyses are capable of capturing the second mode frequency (f\({}_{2}\)) at two sites: S3H and S1U. Figure 7 illustrates that the SAs obtained from both the 1D and 2D ground response analyses exceed the reference spectra defined by the IBC for subsoil category B. In addition  
Figure 8: Comparison of f\({}_{0}\), f\({}_{1}\) from 1D analyses (green circles and squares) and 2D analyses (red circles, squares, and triangles) and theoretical ones (black circles, squares, and triangles). The inversion V\({}_{\mathrm{S}}\) sites are indicated (full black points). to this general observation, it is important to analyse the five individual sites, divided between the hospital (H) and university (U) areas. Compared to 1D, the 2D analysis results in a more attenuated spectrum at low periods and shows a secondary peak around 0.6 s. S1H (shallow V\({}_{\text{S}}\) inversion): The 2D model predicts more pronounced spectral accelerations around 0.3 s. The analyses of the university area (U) show the following evidence: S3U (V\({}_{\text{S}}\) increasing with depth)--the spectral accelerations are comparable between the 1D and 2D models; S1U (significant surface inversion with a thick layer)--the 2D analysis shows stronger amplifications around 0.25 s.  
Figure 8 combines the results reported in Figure 6 with the theoretical ones obtained under the assumption of an ideal viscoelastic homogeneous layer over a deformable substrate, highlighting the sites where a VS inversion was identified. Only the S1H site shows an amplitude that deviates significantly from the theoretical values in both types of numerical analysis within the fundamental frequency f\({}_{0}\) range for the study. In the f1 frequency range, there is strong dispersion of the values, both in terms of the amplification levels and the type of numerical analysis. At the third frequency range f\({}_{2}\), only the 2D numerical analysis is able to capture significant amplifications that exceed those in the theoretical case--but only at the two sites where a V\({}_{\text{S}}\) inversion is present. These results are discussed in light of the relevant literature. The same authors [19] highlight that a homogeneous (i.e., simplified) equivalent profile often leads to the over- or underestimation of true amplification for vibrational modes beyond the fundamental one. The findings of this study support the need to adopt the 'high road'--that is, using site-specific seismic response analyses and a detailed subsurface model--instead of relying on the simplified approach of NTC2018, which classifies subsurface conditions based only on average velocity values and thus tends to homogenise the subsurface. According to [19], Figure 8 shows that, for inhomogeneous soils, the 'equivalent' homogeneous approximation remains a promising solution for the amplitude at f\({}_{0}\). However, the resonant amplitudes may be significantly overestimated or underestimated when an equivalent homogeneous soil approach is used, especially at higher resonances. In this study, at the S1H site, both the frequency and amplification are inadequately estimated when 'equivalent' homogeneous approximations are used.