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

Abstract

Abstract. Multi-hazard risk assessments for building portfolios exposed to earthquake shaking followed by a tsunami are usually based on empirical vulnerability models calibrated on post-event surveys of damaged buildings. The applicability of these models cannot easily be extrapolated to other regions of larger/smaller events. Moreover, the quantitative evaluation of the damages related to each of the hazards type (disaggregation) is impossible. To investigate cumulative damage on extended building portfolios, this study proposes an alternative and modular method to probabilistically integrate sets of single-hazard vulnerability models that are being constantly developed and calibrated by experts from various research fields to be used within a multi-risk context. This method is based on the proposal of state-dependent fragility functions for the triggered hazard to account for the pre-existing damage, and the harmonisation of building classes and damage states through their taxonomic characterization, which is transversal to any hazard-dependent vulnerability. This modular assemblage also allows us to separate the economic losses expected for each scenario on building portfolios subjected to cascading hazards. We demonstrate its application by assessing the economic losses expected for the residential building stock of Lima, Peru, a megacity commonly exposed to consecutive earthquake and tsunami scenarios. We show the importance of accounting for damage accumulation on extended building portfolios while observing a dependency between the earthquake magnitude and the losses derived for each hazard scenario. For the commonly exposed residential building stock of Lima exposed to both perils, we find that classical tsunami empirical fragility functions lead to an underestimation of predicted losses for lower magnitudes (Mw) and large overestimations for larger Mw events in comparison to our state-dependent models and cumulative damage method.

Between global risk reduction goals, scientific-technical capabilities and local realities: a novel modular approach for multi-risk assessment

“…First, the physical-structural and non-structural characteristics of buildings are identified (e.g., Geiß et al, 2017;Aravena Pelizari et al, 2021) and in the following their vulnerabilities are estimated (e.g., physical vulnerability, Gómez Zapata et al, , 2022a. In particular, when working with multi-hazard events dynamically changing vulnerabilities considering cumulative damages, e.g., on buildings caused by earthquakes and tsunamis, need to be assessed (Gómez Zapata et al, 2022bZapata et al, , 2023.…”

“…In order to assess the damage states of the residential buildings and losses after the occurrence of the selected earthquake the so-called damage exposure update (web) service DEUS is triggered (Brinckmann et al, 2021). Using an updated exposure model that includes earthquake-induced damages, and simulations of tsunami inundation depth as inputs, once again the DEUS web services is initiated in order to approximate the expected cumulative damage and disaggregate the losses per hazard event (Gómez Zapata et al, 2023). This methodology makes use of inter-scheme damage compatibility matrices, that can be consulted in Gómez Zapata et al (2022c); and a set of state-dependent tsunami fragility functions (Gómez Zapata et al, 2022d), that for the case of Lima Metropolitan area were constructed after having modified the analytically derived ones originally proposed in Medina (2019).…”