An operators at San Onofre nuclear plant say the facility can withstand a higher magnitude earthquake than scientists predict could ever strike the plants.
The plant near Oceanside can handle earthquakes of magnitude up to 7 and 7.5, respectively, according to an operator.
Americans have become increasingly concerned about domestic facilities in the wake of fears of nuclear crisis in Japan.
Earthquakes and a tsunami have damaged at least two nuclear complexes in Japan and officials have declared states of emergency at six of the country's 55 reactors.
Copyright AP - Associated Press