SL-1, SL-2
SL-1, SL-2 : Levels of ground motion (representing the potential effects of earthquakes) considered in the design basis for a facility. SL-1 corresponds to a less severe, more likely earthquake than SL-2. In some States, SL-1 corresponds to a level with a probability of 10-2 per year of being exceeded, and SL-2 corresponds to a level with a probability of 10-4 per year of being exceeded