Variable-resolution building exposure modelling for earthquake and tsunami scenario-based risk assessment. An application case in Lima, Peru

Abstract

Abstract. We propose the use of variable resolution boundaries based on Central Voronoi Tessellations (CVT) to spatially aggregate building exposure models for risk assessment to various natural hazards. Such a framework is especially beneficial when the spatial distribution of the considered hazards present intensity measures with contrasting footprints and spatial correlations such as in coastal environments. This proposal avoids the incorrect assumption that a single intensity value from hazards with low spatial correlation (e.g. tsunami) are considered as representative within large sized geocells for physical vulnerability assessment, without, at the same time, increasing the complexity of the overall model. We present decoupled earthquake and tsunami scenario-based risk estimates for the residential building stock of Lima (Peru). We observe that earthquake loss models for far-field subduction sources are practically insensitive to the exposure resolution. Conversely, tsunami loss models and associated uncertainties depend on the spatial correlations of the hazard intensities as well as on the resolution of the exposure models. We observe that for the portfolio located in the coastal area exposed to both perils in Lima, the ground-shaking dominates the losses for lower magnitudes whilst the tsunami does for the larger ones. For the latter, two sets of existing empirical flow-depth fragility models are used, finding large differences in the losses. This study arises awareness about the uncertainties in the selection of fragility models and aggregations entities for exposure modelling and loss mapping.

Comment on nhess-2021-70

“…The fragility models of Suppasri et al, (2013) predict larger values with respect to the model proposed by De whose functional values were found within the range as if flow velocity was accounted. These findings are in 460 line with the observations of Park et al, (2017);and Song et al, (2017). These studies concluded that flow-depth models predict larger probabilities of complete damage for buildings than models which that addressed tsunami velocity in their derivation.…”

Impact of exposure spatial resolution on seismic loss estimates in regional portfolios

“…Other methods focused on the exposure component and associated soil properties; this includes manipulating data (i.e., relocation - Bazzurro and Park 2007) or refining data's spatial resolution (i.e., disaggregation -Dabbeek and Silva 2020). More recent spatial representation of exposure suggested using Central Voronoidal Tessellations (CVT) to create exposure models with variable spatial resolutions (Gomez-Zapata et al 2021;Pittore et al 2020). This study will focus mainly on portfolio relocation and disaggregation methods as a way to treat the bias in risk arising from low spatial resolution.…”

Scenario-based multi-risk assessment from existing single-hazard vulnerability models. An application to consecutive earthquakes and tsunamis in Lima, Peru

“…For such a purpose, we recommend using variable-resolution exposure models in the form of central Voronoi tessellations (CVTs). Besides spatially representing the building portfolio, they also provide a representative IM per geocell for reliable and computationally efficient vulnerability estimations (Pittore et al, 2020;Gomez-Zapata et al, 2021e). They also implicitly serve as common minimum reference unit (MRU) aggregation entities between exposure and hazard (Zuccaro et al, 2018).…”

“…We use the dataset compiled by Gomez- Zapata et al (2021e), which is composed of six earthquakes with moment magnitudes ranging from 8.5 to 9.0 M w , which were made available in Gomez- . In that dataset, each event is represented by an associated 1000 realisations of crosscorrelated ground motion fields (GMFs) for peak ground acceleration (PGA) and spectral accelerations (S.A.) at 0.3 and 1.0 s. The selection of these spectral periods depends on the fragility function's IM associated with the building classes of the exposure model (Sect.…”

“…The second approach is jointly applying a number of different building classifications per individual hazard to the same exposed buildings (e.g. Gomez-Zapata et al, 2021e;Arrighi et al, 2022). Their associated fragility functions may have different sets of damage states (differing in number and description).…”