Earthquakes may reach higher magnitudes than California nuclear facilities were designed to withstand, say geologists applying recent advances in seismic science. New seismic technology and observations indicate the potential for greater earthquake risk near the state’s nuclear power plants. Geologists are finding that faults have the potential to rupture across much longer lengths than previously thought, Holly Ryan, U.S. Geological Survey geologist, told Current. Longer ruptures produce stronger earthquakes, she said. Earthquake studies traditionally have been limited in geographic scope to fault network segments, not taking into account the potential for ruptures along whole fault zones, according to the scientists. For instance, at Diablo Canyon, past studies of the earthquake hazards have focused just on a limited segment of what is a longer fault system, according to U.S. Geological Survey research geologist Sam Johnson. “It is not surprising we underestimate the potentiality of the fault systems,” Senator Sam Blakeslee (R-San Luis Obispo) said. New earthquake science has implications for the future of both Pacific Gas & Electric’s Diablo Canyon plant and Southern California Edison’s San Onofre Nuclear Generating Station. San Diego Gas & Electric owns 20 percent of the San Onofre facility; Edison operates the plant. PG&E has a pending 20-year license extension for its Diablo Canyon nuclear plant before the Nuclear Regulatory Commission. Federal regulators may or may not consider the new earthquake data in that license extension. The updated seismic forecast is not necessarily due before the federal commission completes Diablo Canyon’s final safety assessment--expected May 23--and environmental impact statement--due in January 2012. NRC relicensing manager Nathaniel Ferrer said the documents could be “revisited” before the commission takes final action on extending the plant’s license. “We would be very interested in any information that could have a bearing on the seismic safety of the plants,” said NRC spokesperson Victor Dricks. He explained that whether or not the updated earthquake forecast is completed before NRC acts on Diablo Canyon, the federal agency would examine it and require PG&E to modify the plant to assure seismic safety. The same would go for San Onofre, he indicated. Utility representatives maintained the two reactors are seismically sound and guarded against tsunamis. Edison spokesperson Christopher Abel said the company’s most recent seismic analysis, conducted between 2009 and 2011, shows its reactor “has appropriate engineering features, processes, and procedures to protect the public in the event of a maximum credible earthquake.” San Onofre was built to withstand a 7.0 earthquake, Edison officials have said in recent public meetings since the Japanese earthquake. While the upcoming forecast is expected to shed more light on what is a fully unknown earthquake potential at Diablo Canyon, Ryan said at San Onofre emerging analysis shows the well known Inglewood-Newport-Rose Canyon Fault could trigger a magnitude 7.2 shaker. It runs from Los Angeles down to San Diego. In addition, an offshore blind thrust fault that runs from Laguna Beach to Mexico could create a magnitude 7.6 quake, she said. The two faults have different tsunami potentials, she explained. The Inglewood-Newport-Rose Fault is of the strike-slip variety that moves laterally, so it is unlikely to generate any significant tidal wave. On the other hand, the thrust fault--dubbed “blind” because it’s covered by earth--moves vertically and has the potential to create a significant tsunami, she said. Johnson said he thinks the well-known Hosgri fault still may present the biggest earthquake hazard at Diablo Canyon. It’s like the more recently discovered Shoreline Fault there, which is short and segmented, he explained. In contrast, he continued, the Hosgri Fault--which runs 2.5 miles offshore--is part of a continuous network of faults that runs about 250 miles between Point Concepcion and Bolinas. “From my perspective, that’s a bigger concern than the Shoreline Fault,” he said. PG&E maintains its plant is built to withstand a 7.5 magnitude quake. Johnson pointed out that the entire fault zone of which Hosgri is part could rupture, producing a large quake, perhaps large enough to indirectly create a tsunami. “There’s a potential for submarine landslides off the coast of Diablo Canyon,” he said. A strong quake could trigger such a landslide along the edge of the continental shelf where the bottom of the ocean drops down suddenly like a hill, he explained. The geologist estimated such an undersea landslide could trigger a tsunami “several” meters high. State geologist John Parrish told a state legislative committee March 21 that “some models predict in Los Angeles a 40-foot wave based on an offshore landslide. This is about a one-in-3,000-year event.” There is a 30-foot high wall around San Onofre. Southern California Earthquake Center geophysicist Ken Hudnut said that a San Andreas Fault earthquake scenario study in 2008 assessing a 7.8 magnitude quake may not represent the biggest shaker that could occur on the massive fault, which runs from Mexico through San Francisco (Current, March 18, 2011). He said a quake along its southern portion could be as great as magnitude 8.1 if a long enough rupture occurs. Two California Public Utilities Commission members March 24 called for a hearing on the state’s nuclear plants that consolidates seismic and rate issues now dealt with in various dockets. CPUC member Tim Simon said the issues should be aired publicly in light of the Japanese earthquake, tsunami and nuclear plant fallout. Commissioner Catherine Sandoval pointed out that the state nuclear plants’ structure and redesign needs to be reevaluated in light of “multiple risks and cascading events.” “There is an odd division of cost and safety,” she added, but they should be inextricably linked.
