Increasing number of power supply interruptions due to earthquakes leads to heavy direct and indirect economic losses and indicates the importance of resilience of electric power networks. The present study, focusing on seismic resilience of the electricity transmission grid, is looking to develop a basic framework for calculating power grid performance and resilience. This research, based on the network performance analysis and the graph theory, is using a prototype model of the electricity transmission grid to calculate the average performance of the system over recovery time, as the system resilience. This research distinguishes between the damaged facilities in the network by classifying damage levels to different degrees between zero and one and assigning performance values to each level to go beyond the binary statement of connectivity analysis, while having fast and simple calculations.