## 5 Results and Discussion  
In Figure 4, we show the velocity profiles from the tomographic inversion of all wavefields relative to the three lines acquired in Kastela, while in Figure 5, we show those relative to the two lines acquired in Ferrara. The two velocity profiles show very different features. In Kastela, below a slower weathered layer, the velocity rapidly increases to 4.5 km/s and 3.0 km/s for P- and S-waves, respectively. Furthermore, we observe an overall increase in the velocities in the eastern lines (Lines 2 and 3) compared to the western line 1. In Figure 4d-f, we show the SH-velocity profiles and the corresponding V\({}_{\text{S30}}\). Since the velocity is \(>\)800 m/s along all three profiles, we conclude that the soil can be classified as A-class following the Eurocode-8 provisions [9]. In the bottom-right corner of each velocity profile, the mean RMS error is reported. All profiles present a mean RMS lower than 5%, except for the P-wave profile of line 2. This is probably due to the low signal-to-noise ratio of the data caused by the rainfall during the acquisition. Having said this, all other profiles show low mean RMS and can therefore be considered reliable. Figure 3: Examples of first-break picking on common shot gathers. Highlighted in red are the picked travel times. (**a**) P-waves from the Croatian site. (**b**) SH-waves from the Croatian site. (**c**) P-waves from the Italian site. (**d**) SH-waves from the Italian site. Figure 4: Results of the tomographies in Croatia; in the bottom-right corner, the value of the mean RMS error is shown. **(a)** Line 1, P-waves, **(b)** Line 2, P-waves, **(c)** Line 3, P-waves, **(d)** Line 1, SH-waves and V\({}_{\text{S30}}\), **(e)** Line 2 SH-waves and V\({}_{\text{S30}}\), **(f)** Line 3 SH-waves and VS30, **(g)** Line 1 SV-waves, **(h)** Line 2 SV-waves, **(i)** Line 3 SV-waves. In Figure 4, we show the velocity profiles relative to all wavefields for the two lines acquired in Ferrara. We observe a horizontal layering of the sediments, which is typical of alluvial plains. The highest velocities are reached in Line 2, where they exceed 2 km/s and 0.3 km/s for P- and S-waves, respectively. The V\({}_{\rm S30}\) is shown in Figure 4c,d, and it shows values for which the soil can be identified as C-class (V\({}_{\rm S30}>\)180 m/s) following the Eurocode-8 provisions [9], matching the estimates performed in the area by previous large-scale studies [31]. This value and the velocity profile at the center of the line (where the 1D S-wave velocity profile from the MASW is ideally located) is compatible with the results of the inversion of the surface waves, confirming the reliability of our results. The sharp transition at approximately 3 m depth from blue to green in both P-wave velocity profiles most likely indicates the water table. This is consistent with previous geotechnical investigations in the area [32]. Similarly to Figure 4, the mean RMS error is shown in the bottom-right corner of each velocity profile. The values are quite variable, depending on the signal-to-noise ratio of the datasets, which depended on the amount of activities ongoing in the fields. Having said this, they usually show quite a low value, in the range of 5%, and therefore, the velocity profiles can be considered reliable. Further information about the sites can be obtained by computing the V\({}_{\rm P}\)/V\({}_{\rm S}\) ratio (proxy for Poisson's ratio). In Figure 6a-c, we show the V\({}_{\rm P}\)/V\({}_{\rm S}\) profiles relative to the three lines acquired in Croatia, while in Figure 6d,e, we show those relative to the lines acquired  
Figure 5: Velocity profiles from the Italian site; in the bottom-right corner, the value of the mean RMS error is shown. **(a)** Line 1 P-waves, **(b)** Line 2 P-waves, **(c)** Line 1 SH-waves with V\({}_{\rm S30}\), **(d)** Line 2 SH-waves with V\({}_{\rm S30}\), **(e)** Line 1 SV-waves, **(f)** Line 2 SV-waves. in Italy.