## 2 Materials and Methods  
### Site Characterization  
The dynamic characterization of the subsoil is critical in various geotechnical and seismic engineering applications. Among the techniques commonly employed for this purpose, the Multichannel Analysis of Surface Waves (MASW) and Horizontal-to-Vertical Spectral Ratio (HVSR) methods are widely recognized for their efficiency, reliability, and cost-effectiveness in providing essential subsurface information. The MASW technique is widely used due to its non-invasive nature, and the relatively quick acquisition and processing times required for generating reliable results [26]. The method examines surface wave propagation to determine the 1D shear wave (Vs) velocity profile of the subsurface. By analyzing the surface wave dispersion curves, this method provides a robust estimate of the Vs structure, which is essential for assessing the stiffness and dynamic behavior of the site. The HVSR method [27] is based on the spectral ratio between horizontal and vertical components relative to environmental seismic noise recordings made through passive seismic single-station surveys. This method is widely used to identify the site resonance frequency, related to sediment thickness overlying the bedrock, giving information on the possible overall site response during seismic events. The minimal equipment and data processing required make this technique an excellent tool for rapid and large-scale surveys [28]. The complementary use of MASW and HVSR methods enhances their application in site characterization. Their use in various geological and environmental contexts has amply validated their ability to produce consistent and accurate results on subsurface conditions with minimal investment in time and resources [29; 30; 31; 32]. Four passive single-station seismic recordings were carried out at different points in the area surrounding the bell tower (Figure 2a) to identify the site resonance frequencies and verify the possible presence of lateral variations in the subsoil characteristics. The environmental seismic noise was acquired at a sampling rate of 128 Hz for 16 min at each recording site. The recordings were performed using four portable three-component digital seismometers, which allowed all measurements to be taken in the same time frame. Signals acquired were subsequently processed using the HVSR technique. Each recorded signal was divided into time windows of 20 s, selecting the stationary part and removing the transient. Fourier spectra were calculated in the frequency band 0.5-20.0 Hz and smoothed using a Triangular window with a smoothness of 10% (Figure 2b). In addition to the passive single-station surveys, a MASW survey was carried out to the east of the bell tower, in an area lower than the street level, behind the nearby cathedral (Figure 2a). The choice of the site where to carry out the survey was made considering the need to bypass the effect of the square floor where the bell tower is located, thus attempting to effectively investigate the subsoil characteristics without interference from the anthropized layer. The survey was carried out using 24 vertical geophones, with a frequency of 4.5 Hz, positioned at a distance of 1.5 m from each other, for a total array length of 34.5 m. The energizations were carried out at 3 and 6 m from the first and last geophones using an 8 kg sledgehammer. Five shots were performed at each energization point to increase the signal-to-noise ratio (vertical stacking). The acquired signal was analyzed in the frequency-phase velocity domain to isolate the energy associated with Rayleigh waves. Assuming a predominance of surface waves in the wave field, the Vs-depth profile for the investigated area was derived after obtaining the dispersion spectrum of Rayleigh waves through MASW processing. This was achieved by performing a joint fit between the dispersion spectrum and an H/V spectrum acquired near the alignment. The combination of these two techniques is based on their complementary strengths.