Uncertainties in Seismic Risk Assessment at Urban Scale. The Case of Thessaloniki, Greece

Seismic risk assessment and loss estimation are of major importance for decision-making with respect to the reduction of earthquake-induced losses in large urban areas. However, the methodological chain of seismic risk assessment, from seismic hazard assessment to evaluation of potential losses, encompasses both aleatory and epistemic uncertainties associated with different sources. The present study aims to give an insight into epistemic uncertainties in seismic risk assessment at urban scale when applying the Capacity Spectrum Method (CSM), using the city of Thessaloniki, Greece as a case study. Quantification of uncertainties related to structural capacity and fragility curves parameters was performed using a logic tree approach. A sensitivity analysis of the computed seismic risk results was also performed in order to determine which input parameters have the greatest impact on the output. For the considered set of input parameters, it was found that the epistemic uncertainties related to damage states thresholds of the fragility curves are the most significant ones, while those associated with the capacity curve parameters may also be substantial. On the contrary, the sensitivity of computed seismic risk on CSM parameters a1, a2 and γ appears to be negligible. The results highlight the critical points to which special attention should be paid when implementing the Capacity Spectrum Method for seismic risk assessment.