Quantifying the Impacts of Incorporating Damage Correlation on Scenario‐Based Regional Seismic Assessment

One of the key challenges in applying the performance‐based earthquake engineering framework at a regional scale is accounting for structure‐to‐structure damage correlation, which is commonly neglected in regional risk assessment. This correlation reflects the tendency for buildings in the same area, often constructed with similar materials, design practices, and vulnerabilities, to exhibit similar damage states after an earthquake. In this study, damage correlation was estimated using a method based on correlated Bernoulli trials, with marginal and joint damage probabilities derived from non‐linear time history analyses. Specifically, multiple stripe analysis on detailed 3D building models and incremental dynamic analysis on equivalent single‐degree‐of‐freedom oscillators were employed to obtain these probabilities. To evaluate the implications of incorporating this correlation in regional analysis, a case study was conducted on mid‐rise reinforced concrete frame buildings in the province of Caserta, Italy. Results show that while the inclusion of correlation has little impact on the mean and median estimates of damaged buildings for a given scenario, it significantly influences the dispersion and tail behaviour of the damage distribution, increasing the likelihood of widespread damage. These findings highlight the importance of accounting for damage correlation in regional seismic risk analyses to support more accurate loss estimates and better‐informed mitigation strategies. Summary The impact of incorporating building‐to‐building damage correlation in scenario‐based regional seismic assessments is investigated—a factor often neglected or oversimplified. A case study in southern Italy is used to apply the proposed methodology, estimating correlation via correlated Bernoulli trials and joint damage probabilities derived from non‐linear time history analyses. Results demonstrate that accounting for damage correlation significantly affects damage estimates, laying the groundwork for scalable applications in future large‐scale seismic risk assessments.