On the treatment of uncertainty in seismic vulnerability and portfolio risk assessment

Abstract

SummaryIn a related study developed by the authors, building fragility is represented by intensity-specific distributions of damage exceedance probability of various damage states. The contribution of the latter has been demonstrated in the context of loss estimation of building portfolios, where it is shown that the proposed concept of conditional fragility functions provides the link between seismic intensity and the uncertainty in damage exceedance probabilities. In the present study, this methodology is extended to the definition of building vulnerability, whereby vulnerability functions are characterized by hazard-consistent distributions of damage ratio per level of primary seismic intensity parameter-Sa(T 1 ). The latter is further included in a loss assessment framework, in which the impact of variability and spatial correlation of damage ratio in the probabilistic evaluation of seismic loss is accounted for, using test-bed portfolios of 2, 5, and 8-story precode reinforced concrete buildings located in the district of Lisbon, Portugal. This methodology is evaluated in comparison with current state-of-the-art methods of vulnerability and loss calculation, highlighting the discrepancies that can arise in loss estimates when the variability and spatial distributions of damage ratio, influenced by ground motion properties other than the considered primary intensity measure, are not taken into account. KEYWORDS damage ratio uncertainty and spatial correlation, event-based seismic loss estimation, hazard-consistent fragility and vulnerability | INTRODUCTIONIn the process of risk computations, several studies have demonstrated the importance of accounting for spatial cross correlation of ground motion residuals in the evaluation of portfolio losses (eg, Park et al, Weatherill et al, Silva, and Yoshikawa and Goda 1-4 ). However, when the correlation of uncertainty in vulnerability (ie, in the damage ratio residuals across a class of buildings) is incorporated in loss estimation procedures (eg, Silva et al 5 ), it is done such that when sampling the uncertainty in the vulnerability of 2 assets with the same building class (and same level of seismic intensity measure), the residuals are assumed to be either uncorrelated of perfectly correlated. 6 Furthermore, as demonstrated by Bradley 7 and Silva et al 8 in the context of component and building fragility, respectively, the propagation of uncertainty from fragility to vulnerability is related to the scatter of results to which a parametric (usually lognormal) fragility curve is fitted (ie, uncertainty associated with the regression; Figure 1A).Typically used parametric relationships such as the lognormal or beta probabilistic functions provide a good approximation to the vulnerability uncertainty that results from the scatter of possible fragilities ( Figure 1B; eg, Silva et al 5 ). For a given level of

Uncertainty and Correlation in Seismic Vulnerability Functions of Building Classes

“…Similar distributions of LR were also analytically verified by Sousa et al (2018) and empirically reported by Taylor (2015). The challenge now becomes how to develop a statistical model capable of accurately propagating this uncertainty in seismic risk analysis while ensuring a satisfactory computational performance.…”

“…The consideration of these three sources of uncertainty in the derivation process leads to vulnerability functions that can be represented by a probabilistic distribution of LR per each IM (e.g., Sousa et al 2018), as opposed to a deterministic LR for each IM . Despite the recognition of this uncertainty (e.g., Porter 2010, Taylor 2015, Sousa et al 2018), the vast majority of probabilistic seismic risk studies consider vulnerability functions as deterministic. This practice can lead to an underestimation of the variability in earthquake losses (e.g., Silva 2016).…”

Time-dependent seismic hazard and risk due to wastewater injection in Oklahoma

“…In our study, however, we utilized spatially aggregated groups of buildings and loss ratio curves (Figure 6), instead of fragility functions. Further discussion on the effects of loss correlation on the rate of exceedance of portfolio losses can be found in Sousa et al (2018).…”

Dynamic Decision Model of Real Estate Investment Portfolio Based on Wireless Network Communication and Ant Colony Algorithm

“…In the related research carried out by Sousa et al, building fragility is expressed by strength: the specific distribution of damage exceeding probability of various damage states. The latter contribution has been demonstrated in the context of building portfolio loss estimation, which shows that the proposed concept of conditional vulnerability function provides a link between earthquake intensity and the uncertainty in the probability of damage exceeding [6]. For the above situation, Orlando and Parker focus on assessing the financial status of insurance companies issue variable annuity (VA) portfolios.…”