Preliminary seismic fragility assessment of power systems in major Korean cities

Transmission networks are essential to urban functionality, and the failure of a single component during an earthquake can disrupt electricity supply to critical facilities. However, previous studies have focused mainly on component-level fragility, and system-level comparisons of urban transmission networks remain limited. This study presents a connectivity-based probabilistic system-level fragility assessment of transmission networks in five major South Korean cities. An existing framework was extended and applied consistently to enable direct intercity comparisons. City-level indicators, namely the median and the high confidence of low probability of failure, were derived from fragility curves of power plants and substations. A sensitivity analysis identified the components with the greatest influence on network reliability. A path-level analysis examined how the number of components and the proportion of vulnerable components affect failure probability. Because identical fragility curves were applied to all cities, the comparison isolates the influence of network topology. Intercity differences were governed primarily by the proportion of paths traversing the highest-importance components. System-level seismic performance therefore cannot be inferred from component fragility alone and is strongly shaped by network configuration. These results support retrofit prioritisation, cost-effectiveness assessment of new substations or routes, and seismic risk management of urban power systems.