Seismic risk

The question is not if but when Southern California will be hit by a major earthquake – one so damaging that it will permanently change lives and livelihoods in the region.” – United States Geological Survey 2008.

The March 11, 2011, earthquake and tsunami that destroyed the Fukushima-daiichi nuclear power plant in Japan has raised worldwide concern about the seismic risks to nuclear reactors. Decades before the Fukushima nuclear catastrophe, however, there were widespread concerns over the earthquake risk at the San Onofre nuclear reactor site. The reactors are located in an area of active seismic activity on the Pacific coast of Southern California. The two reactors at the site were originally designed to withstand a magnitude-6.5 earthquake. After citizen groups in the mid-1970's challenged these standards, Southern California Edison “redesigned” the plant to take account of a magnitude-7.0 earthquake.

Edison stated that a higher-than-7.0-magnitude seismic event is “not credible.” But in recent years it has been confirmed that an earthquake of magnitude 7.5 or greater centered in Southern California could occur. That is an earthquake potentially five times more powerful than what Edison considered the maximum possible magnitude when it rebuilt the San Onofre reactors.

In the late 1970's, Friends of the Earth and local citizens challenged the operating licenses for the San Onofre reactors, which were scheduled to begin operation in the early 1980's. One of the principal issues was that the seismic design of the reactors was inadequate to protect public health and safety. The court dismissed these claims, and the reactors began operation in 1982 and 1983.

Three decades since the two San Onofre reactors began operations, it is clear that that the seismic risk at San Onofre remains very real. The major uncertainties regarding the seismology of the San Onofre site relate to the continuity, structure, and earthquake potential of the South Coast Offshore Fault zone and the fault lines that connect the Newport-Inglewood Fault in the Los Angeles region with the Rose Canyon Fault in the San Diego region.

According to the California Energy Commission, "Advances in seismology have revealed that the SONGS (San Onofre) site could experience larger and more frequent earthquakes than had been anticipated when the plant was designed.” While the California Energy Commission also stated that the plant could very likely safely shut down in the event of a major earthquake, it did point out that it had not reviewed the seismic design of San Onofre well enough “to evaluate whether the safety margins at the plant are indeed sufficient to accommodate the maximum ground motions that are now thought to be credible at the site.”

As seen in Japan in 2011, a major earthquake impact on San Onofre could be catastrophic. Should major seismic activity occur in any of the many fault lines near San Onofre, a major meltdown could occur, causing serious damage and creating disastrous public health and environmental concerns.

For further information on the seismic risks to San Onofre, see