<p>Regarding the role of power network in the resiliency of urban areas, it is essential for authorities to have fast estimate of the seismic reliability of electric grid. Therefore, there is an appeal for developing performance fragility curves according to the system operational objectives and also soft and simple methods of power outage analysis instead of sophisticated time-consuming dynamic approaches. In the past, the seismic risk analysis of power network has been evaluated based on individual equipment vulnerability and the power network functionality and outage has been regarded with relatively little concern due to complicacy of power grid system. The present research is focused on two objectives: 1- developing operation-based fragility curves using drift limits as criteria of equipment vulnerability and 2- providing a model for estimating power outage probability due to earthquakes, based on two criteria: I- physical damage of installation resulting in interconnection loss, and II- imbalance of power demand-supply due to partial shut-down of installations within the network and overloading of remaining installations. To develop a seismic fragility model, combined fragility curves of installations are developed using functionality logic of interconnected equipment. The component fragility curves are suggested to be adopted among parametric fragility curves developed in this research. A case study of power outage probability calculation is presented for a part of the greater Tehran. The probability of outage due to physical damage of installations in the study area is estimated around 0.38, 0.62 and 1.00 for 9.5, 72 and 475 years of return period earthquake scenarios respectively. The outage probability is calculated to be around 0.85, 0.91 and 1.00 assuming the imbalance in power demand–supply as the additional cause of power outage.</p>