Exploring the Impact of Spatial Correlations and Uncertainties for Portfolio Analysis in Probabilistic Seismic Loss Estimation

The significant potential for human and economic losses arising from earthquakesaffecting urban infrastructure has been demonstrated by many recent events such as, for example,L’Aquila (2009), Christchurch (2011) and Tohoku (2012).Within the current practice ofseismic loss estimation in both academic and industry models, the modelling of spatial variabilityof the earthquake ground motion input across a region, and its corresponding influenceupon portfolios of heterogeneous building types, may be oversimplified. In particular, thecorrelation properties that are well-known in observations of ground motion intensity measures(IMs)may not always be fully represented within the probabilistic modelling of seismicloss. Using a case study based on the Tuscany region of Italy, the impacts of including spatiallycross-correlated random fields of different ground motion IMs are appraised at varyingspatial resolutions. This case study illustrates the impact on the resulting seismic loss whenconsidering synthetic aggregated portfolios over different spatial scales. Inclusion of spatialcross-correlation of IMs into the seismic risk analysis may often result in the likelihood ofobserving larger (and in certain cases smaller) losses for a portfolio distributed over a typicalcity scale, when compared against simulations in which the cross-correlation is neglected. Itcan also be seen that the degree to which the spatial correlations and cross-correlations canimpact upon the loss estimates is sensitive to the conditions of the portfolio, particularly withrespect to the spatial scale, the engineering properties of the different building types withinthe portfolio and the heterogeneity of the portfolio with respect to the types.