# Measuring the Seismic Resilience of Housing Systems in Italy
## 4 Discussion  
As can be deduced from Figures 4-6, resilience values decrease by increasing the return period while increasing the control time. The reduction in value is due to the lower robustness associated with a higher return period, while the increase in value is connected to the greater recovery for a longer control time. This is intuitive but can also be proved mathematically by applying Equations (5), (6) and (8) for different return periods and control times. As underlined in Section 2, the resilience of a system can be defined as its average functionality level over the considered control time. Accordingly, in addition to indicating time-averaged functional levels, Figures 4-6 may also be viewed as average ULCs over time, which may be recovered during the reconstruction process. Thus, to provide a practical resource of information for policymakers, the obtained results are discussed in terms of average ULCs over the considered control times, referring to the ULC thresholds described in Section 1. For a return period of 100 years (Figure 4), the towns of San Marco in Lamis, Carbone, Marzi, Sassinoro, and Castelvecchio Siculo are the least resilient of Apulia, Basilicata, Calabria, Campania, and Sicily regions, respectively. Conversely, the towns of the Province of Lecce and Brindisi (together with the southeastern towns in Taranto Province), Policoro, Montegiordano, Castellabate (together with Perdifumo and closed towns), and those of the Province Trapani, Caltanisetta, Agrigento (including part of the Enna Province) are the most resilient of the same regions, respectively. According to the ULC thresholds specified  
Figure 6: Resilience assessment for a return period of 500 years considering the following control time \(T_{LC}\): (**a**) 12 months; (**b**) 24 months; (**c**) 36 months; (**d**) 60 months. in Section 1, OLC can be experienced in many towns of the five regions for different control times. However, due to the low resilience values (<50%) of some towns in the Calabria and Campania regions (highlighted in red in Figure 4a), ELC can be experienced over a control time of 12 months. For these towns, CLC and LSLC could be expected over a control time of 36 (Figure 4b,c) and 60 (Figure 4d) months, respectively. Considering the first 12 months (Figure 4a), CLC can be exhibited in the critical towns of Basilicata and Sicily, while LSLC can be experienced in the most vulnerable towns of Apulia. On the other hand, considering a control time of 60 months (Figure 4d), LSLC could be obtained in the same towns of Basilicata and Sicily, while DLC in those of the Apulia region. Referring to a return period of 250 years (Figure 5), the towns of Carpino, Castelluccio Superiore, Albi, Pietraroja and Ali become the least resilient of Apulia, Basilicata, Calabria, Campania, and Sicily regions, respectively. In these towns and their surroundings, ELC is expected over a control time of 12 months (Figure 5a), and whenincreasing the control time (Figure 5b-d), better ULCs are obtained, especially for the towns of Apulia followed by those of Sicily, where LSLC is expected considering a control time of 60 months. The critical towns of Basilicata and Campania exhibit ELC for a control time of 24 months and CLC for a control time of 36 and 60 months. In the most critical town of Calabria, ELC is experienced for a control time of 24 and 36 months, while CLC is expected to have a control time of over 60 months. For each control time, the most resilient towns of the analyzed regions (highlighted in light green, green and dark green in Figure 5) exhibit a DLC in Basilicata and Campania and an OLC in Apulia, Campania and Sicily. Finally, for a return period of 500 years (Figure 6), the towns of Celenza Valforte, Carbone, San Basile, Sassinoro and Mandanici can be considered as the least resilient of Apulia, Basilicata, Calabria, Campania, and Sicily regions, respectively. These critical towns and their surroundings exhibit ELC for the first 36 months (Figure 6a-c) and experience CLS over a control time of 60 months (Figure 6d).