Seismic Information

Seismic Safety

PG&E remains focused on ensuring that Diablo Canyon continues, and improves upon, its strong record of safe operations. This includes making the facility resilient to natural hazards, including earthquakes and tsunamis.

PG&E is the only utility in the country that employs a seismic department staffed with experts. The scientific staff continually studies earthquake faults in the region of the power plant and global seismic events as part of the plant's comprehensive safety program.

In November 2008, the U.S. Geological Survey (USGS), working in partnership with PG&E's geosciences department, discovered a new shoreline fault zone, and PG&E evaluated whether that new feature presented a safety risk to the plant. PG&E submitted its evaluation to the Nuclear Regulatory Commission (NRC) under the commitment of its current operating licenses. PG&E's evaluation confirmed the plant has adequate safety margin to withstand maximum ground motions postulated to occur from faults in the region, including the shoreline fault.

Advanced Seismic Research

PG&E is currently conducting advanced seismic studies that will provide a more accurate and detailed picture of the region’s complex geology. The research, called for by the state, will help further define the amount of ground motions that seismic faults in the region are capable of producing.

PG&E has made steady progress toward completing the studies since the research began in 2010. The on-shore work is nearly complete, the majority of the low-energy off-shore studies are finished, and the California Coastal Commission has approved PG&E’s request to install ocean-bottom seismometers to detect seismic activity.

The company plans to undertake the final, off-shore high-energy study as soon as it obtains all necessary permits from various regulatory agencies, including the State Lands Commission, California Coastal Commission and County of San Luis Obispo. To address public concern regarding the seismicity of the area surrounding Diablo Canyon, PG&E has worked to expedite the permitting process so it can begin this study as soon as possible. PG&E is committed to conducting this work safely and in a manner with the least impact to the community and the environment.

Once the research is complete, PG&E will use the data to support its ongoing work to continually assess and validate the seismic design of the plant. PG&E will also share information collected with local public and government agencies so they can incorporate it into emergency preparedness plans and ensure the safety of critical infrastructure. The data will also be used to support federal requirements for new seismic risk evaluations following the Fukushima Daiichi power plant tragedy in Japan.

Seismic Studies Update

During the week of August 20, 2012, PG&E will resume low-energy seismic research work off portions of California's Central Coast.

PG&E began the first phase of this low-energy offshore study in 2010, and completed the second portion in 2011. The third phase will study areas near San Luis Bay, Estero Bay and Point Sal.

All operations will be performed during daylight hours and processes and procedures have been implemented to monitor and protect marine mammals while the study is underway.

Mariner and commercial boat traffic are encouraged to remain at least a mile away from the vessel while it operates in the area to avoid entanglement with research equipment. Daily updates on the location of the vessel can be found at using the search word "Pacific Star."

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