# Vulnerability and Seismic Exposure of Residential Building Stock in the Historic Center of Alcamo
## 7 Results  
The results obtained based on the compartment-scale survey, using the procedure described above, are initially shown. Figure 7a compares the average damage curves, as the macrosieismic intensity changes, for the typologies of the historic center, obtained with the vulnerability index evaluated by the compartment- (solid line) and building- (dotted line)-scale surveys, respectively. The curves show, for fixed seismic event intensity, the greater expected damage in higher-vulnerability masonry buildings (MUR1), the lower propensity for damage in buildings with RC on good-quality masonry (MUR23_SCA), the effectiveness of masonry confinement in reducing the expected damage (MUR3_CONF), which is close to that expected in non-seismically designed RC buildings (CAR1), and the reduced damage expected in RC buildings designed in accordance with the recent earthquake-resistant legislation (CAR3). A comparison between the curves obtained with the two different scales of the survey campaign highlights the significant increase in the average damage expected for the masonry types, above all for the more vulnerable MUR1 and MUR2, for the survey at the compartment scale, and the negligible variation for reinforced concrete buildings. The fragility curves for masonry buildings with reinforced concrete slabs MUR23_SCA in Figure 7b show how, through the damage distribution probability function presented in Equation (2), it is possible to predict, for each masonry type, the probability to exceed a given damage level as the macrosieismic intensity varies. The increase in the vulnerability index obtained with the survey campaign at the compartment scale compared to that at the building scale presented, as a consequence, a similar increase in the probability of damage overcoming for all levels of damage. The expected damaged based on the compartment-scale survey, using the procedure described above, are initially shown. In more detail, Figure 8 shows the maps of the mean values of the expected damage for two different macrosieismic intensity levels, evaluated based on the data derived through the building-scale survey. The first one, for macrosieismic intensity I = 6 (Figure 8a), roughly corresponding to an earthquake with a return period RP = 30 years, shows that moderate damage is expected for this seismic intensity. In the second one, related to macrosieismic intensity I = 9 (Figure 8b), slightly higher than that corresponding to a return period of 975 years, the number of buildings experiencing substantial-to-severe damage, with moderate structural damage and severe nonstructural damage (D \(\geq\) 3), is significant. Figure 7: Curves of average damage (**a**) and probability of damage level exceedance (**b**) as macrosieismic intensity changes for vulnerability indexes evaluated by compartment- (solid line) and building (dotted line)-scale surveys. Taking advantage of the relationship presented in Equation (7), which links the macroseismic intensity to the seismic acceleration peak value, and the seismic hazard estimation provided in the present Technical Standards for Construction (MIT, 2018), assuming that, in a simplified way, the entire historic center is built on category-B soil (stratigraphic amplification coefficient S = 1.2), it was possible to provide an estimate of the foreseeable damage for seismic events with return periods RP of 30, 50, 475, and 975 years, whose corresponding to peak values of the acceleration at the foot of the structure are: 0.04, 0.05, 0.14, and 0.19 g (g = gravity acceleration). The overall data for the entire historic center derived from the compartment-scale analysis are shown for four different seismic action return periods in Figure 9a. The figure shows that, for RP = 50 years, 20% of buildings suffer significant damage to non-structural elements (D \(\geq\) 3), while, for RP = 475 years, more than one third of buildings suffer severe structural damage and very severe non-structural damage (D \(\geq\) 4).