Operating basis earthquake (OBE)

The earthquake that the structure must safely withstand with no damage. All systems and components necessary to the uninterrupted functioning of the project are designed to remain operable during the ground motions associated with the OBE. This includes the dam, appurtenant structures, electrical and mechanical equipment, relays, spillway gates, and valves. For most usage in Reclamation, the OBE is specified to have a 90% probability of nonoccurrence in a 25-year-exposure period. This is equivalent to a recurrence interval of 237 years. Economic considerations for specific projects may lead to consideration of other values. The earthquake(s) for which the structure is designed to resist and remain operational. It reflects the level of earthquake protection desired for operational or economic reasons and may be determined on a probabilistic basis considering the regional and local geology and seismology.