Substations are among the most vulnerable components when earthquakes occur, and thus models to assess the risk of substation outages in resilience studies are becoming critical. In this context, this paper proposes an approach to model substation outages using a bay-level representation. Hence, substation outages can take many forms depending on the specific configuration of bays unavailable after an earthquake strikes. Thereafter, we simulate the system operation under many outage scenarios and quantify system resilience through various metrics. Our proposal is applied on the IEEE RTS 24-bus and Chilean transmission systems. Furthermore, we compare our proposed bay-level approach with a monolithic method currently used to model substation outages in power system resilience. The results show that the bay-level approach is more practical and accurate for modeling substation outages in power networks.