## 5 Discussion
This discrepancy could be due to a shallow VS inversion and/or a more complex stratigraphic relationship. Other authors [5] show that the effect of a hard upper layer is to exert a confining influence on the soft layer below, leading to two possible outcomes: de-amplification at lower periods and more pronounced amplification at higher periods. For the purposes of this study, both 1D and 2D analyses were conducted, incorporating both lithostrigraphic effects and the complex subsurface geometry, where the influence of V\({}_{\text{S}}\) profile inversion overlaps with the morphological effects. This study confirms that there is significant'scattering' along the frequency spectrum at which amplifications occur, a phenomenon that cannot be predicted a priori using simplified methods. Therefore, a detailed subsurface model is essential to reduce uncertainties in assessing the expected seismic motion at a site. Two-dimensional analyses are particularly useful when studying site effects under complex conditions. Other authors [20; 21] note that 3D geometries significantly increase the complexity of the computed ground motion, making it difficult to draw universally applicable conclusions. However, further analysis could be conducted by considering 3D effects, such as the spatial influence of individual layer shapes, deep layers (e.g., bedrock), and seismic source position modelling. From the perspective of the buildings in the study area, it is important to consider the findings of structural studies conducted on the San Salvatore Hospital and the University of Coppito campus. Some authors [22; 23] have assessed the overall condition of the hospital buildings, revealing a heterogeneous level of criticality. The building plan is highly irregular,consisting of several independent reinforced concrete substructures separated by seismic joints. Generally, the joints are designed to ensure regularity in structural rigidity and mass distribution. After the 2009 L'Aquila earthquake, in addition to limited and localised structural damage to portions of three buildings, the most significant systemic issue was with the seismic separation joints. These joints failed to function properly due to inadequate seismic design. The accurate design of seismic joints requires a detailed assessment of the displacements that may occur during a seismic event. These displacements are influenced by the seismic forces acting on the structure and the specific characteristics of the modal behaviour of both the soil and the structure. The university buildings [24] consist of six reinforced concrete substructures separated by seismic joints, and they have distinct H-shaped and C-shaped configurations. Four of the buildings are characterised by geometrical regularities, both in plan and elevation, while the two central structures exhibit higher irregularity. Numerical and experimental analyses [25] were conducted on one of the irregular buildings, revealing three main modal frequencies and shapes: the first mode is translational in the X- and Y-directions with a frequency of 2.7 Hz, and the other modes are roto-translational with frequencies ranging from 2.9 to 3.8 Hz. The structural implications are as follows: (i) assessing the existence of so-called double resonance (i.e., between earthquake, soil, and structure); (ii) identifying structural modes higher than the first that can interact with site effects typical of deposits where morphological complexity is superimposed on velocity inversion; (iii) evaluating whether structural ageing has caused substantial frequency variations; and (iv) ensuring the adequacy of structural joints and nonstructural components where adjacent portions of buildings are present. Finally, for very large structures, it is common for different seismic actions to occur during earthquake shaking, which consequently generates relative input motion at the foundation base.