## 3 Results
### Comparison of the Two Representations  
The two approaches for representing the data shown above allow the localization of points of significant interest for monitoring structures and the subsidence phenomenon. These outcomes cannot be directly interpreted to perform novelty detection due to the limitations of the input data. However, it is possible to compare the results obtained through the two approaches to verify them. In detail, it is investigated how the points with a high-intensity negative velocity are distributed with respect to the values of entropy and energy of the signal. Figure 8a shows that points with higher absolute velocity have lower entropy values, concentrated in the range 0.8-0.82. In contrast, points with velocities close to zero exhibit greater entropy. As the velocity increases beyond 0.5 cm/y, a further decrease in entropy is shown. Figure 8b shows how the energy remains low for velocity values close to zero and increases significantly for lower velocity values. These points correspond to locations subject to accentuated subsidence (beyond the \(\mu-3\sigma\) limit). Hence, in the entropy-energy dispersion, they constitute the decreasing branch on the right (Figure 9). Figure 8: Correlation between LOS velocity and entropy-energy dispersion in the period from 2017 to 2019 for a building complex near San Giovanni station: (**a**) Entropy-velocity dispersion; (**b**) Energy-velocity dispersion. Figure 9: Entropy-energy dispersion for a building complex near San Giovanni station in the period from 2017 to 2019. It can be observed that the experimental data subject to subsidence (low entropy and high energy) show lower variance with respect to the mean model, hence, lower uncertainty, and could be interpreted as signals related to perturbations that are actually moving those points. These points are represented in blue in Figure 10. The figure also shows in red the points that are defined as outliers of the entropy-energy dispersion, which are above the analytical threshold. Their signals show higher entropy than predicted by the mean model; thus, they are subjected to higher complexity and require further investigation, especially those that coincide with subsidence points. For greater accuracy of the results, it would be necessary to identify and exclude any spurious points not related to the area of the buildings. In addition, structural type and features, such as the number of stories, should be investigated to reveal any variations due to dissimilarities between the adjacent structures. However, this can be left out as a consequence of the simplifying assumptions adopted in Section 2. The entropy-energy dispersion can be further discussed by comparing two different periods to study the results before and after tunnel excavation. Given the complete dataset from 2011 to 2019, the following section distinguishes two periods of the same duration: 2011-2015 and 2015-2019. Figure 11 shows the correlation between the entropy-energy dispersion and the LOS velocity in the period from 2011 to 2015. Meanwhile, Figure 12 refers to the period from 2015 to 2019. Figure 11: Correlation between LOS velocity and entropy-energy dispersion in the period from 2011 to 2015 for a building complex near San Giovanni station: (**a**) Entropy-velocity dispersion; (**b**) Energy-velocity dispersion. Figure 10: Map showing the experimental data for a building complex near San Giovanni station. The locations where subsidence is most emphasized and the entropy-energy outliers are highlighted. Figure 11a displays a higher level of scattering than Figure 12a. In addition, velocity values in the period 2011-2015 are more evenly dispersed when compared to the following period, and their intensity in the negative portion is lower, therefore significant subsidence is not observed. Consequently, the entropy-energy dispersion in the first period (Figure 13a) has fewer points on the low entropy-high energy branch with respect to Figure 13b, none of which reaches the limit of subsidence previously evaluated.