GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 of seismic hazard also known as MPS04 (“Mappa di pericolosità sismica” in Italian, proposed by Stucchi et al., 2004; 2011). The measure of ground shaking is the peak ground acceleration (PGA) value with a 10% probability of exceedance in 50 years (i.e., corresponding to a mean return period of 475 years). The considered social vulnerability indicator is used to identify people that may be less likely to respond to, cope with, and recover from a natural-hazard-induced disaster (e.g., Cutter & Finch, 2007); it is typically derived through composite sub-indicators (e.g., Cutter et al., 2003; Yoon, 2012). For this application, we derive the social vulnerability indicator (SoVI) through the approach proposed by Frigerio et al. (2018). The variables used to estimate the SoVI are publicly available in the latest census dataset (Italian National Institute of Statistics; ISTAT 2011) and relate to population, age (e.g., rate of elderly older than 65 years), family structure (e.g., family with more than five members), employment (e.g., unemployment rate), socioeconomic status (e.g., commuting rate), ethnicity (i.e., foreign resident), education and population density. The SoVI indicator assumes values less than 0 (for low social vulnerability) and greater than 1 (for high social vulnerability), as it is obtained as the sum of normalised variables, each one with either a positive (increasing) or negative (decreasing) effect on social vulnerability. The physical vulnerability indicator expresses the susceptibility of buildings and other assets to a particular damage level for a specific hazard (i.e., earthquake) intensity. This indicator is derived using the Risk-UE index-based approach (Lagomarsino & Giovinazzi, 2006) to be consistent with the structure of the social vulnerability term. (The use of score-based approaches for measuring both physical and social vulnerabilities makes them easily aggregable and comparable.) Specifically, this vulnerability indicator ranges between 0 and 1, with values close to 1 indicating the most vulnerable buildings and close to 0 indicating buildings with superior seismic performance. The Risk-UE indicator is derived from basic information on construction material and structural system (masonry type, e.g., simple stone, massive stone; reinforced concrete – RC - frame or walls; etc.) and additional information on vulnerability factors, such as the height of the structure, the type of horizontal structures for masonry buildings and the level of earthquake resistant design (in the case of RC). An initial value of the indicator is defined as a function of the construction material/structural system, which can then be modified based on further information, if available. For example, a value of 0.87 is assigned to masonry buildings with irregular layout, and this value could increase if vaults (+0.08) or flexible slabs (+0.02) characterise the lateral structural system. The information on construction materials can be found in the latest census The other required data are derived by adopting a suitable exposure/vulnerability model that defines rules to assign census building typologies (e.g., classified based on construction material and age of construction) to building classes (Tocchi et al., 2022). In line with the Risk-UE approach, the physical vulnerability indicator is first evaluated at the building type (or class) level, i.e., for each class of buildings with the same structural features. Then, the final municipal-level indicator is obtained as a weighted average based on building class presence in the municipality. The exposed population is also considered part of the RI. This indicator quantifies the residential population at the municipal level derived from the most recent census.We normalise each indicator through their empirical cumulative distribution functions (ECDFs), which express the probability that a random variable X