Seismic Safety and Advanced Seismic Testing

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 employs a seismic department staffed with experts who continually study 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. The 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.

Why is PG&E Conducting 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 was called for by the State of California, and will help further define the level of seismic activity that earthquake faults in the region are capable of producing, including the Shoreline Fault.

To address public concern regarding the seismicity of the area surrounding Diablo Canyon, PG&E has worked to expedite the permitting process for this research so it can complete the studies as soon as possible.

PG&E has made steady progress toward completing the studies since the research began in 2010. The onshore work is nearly complete, the majority of the low-energy offshore 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, offshore high-energy study if it obtains all necessary permits from various regulatory agencies.

What Will PG&E Do With the Information?

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 their respective emergency preparedness plans and ensure the safety of critical infrastructure. The data collected will also support a new, federally mandated seismic risk evaluation. All nuclear power plants are required by the NRC to conduct such an evaluation after the Fukushima Daiichi power plant tragedy in Japan.

When Will the High-Energy Offshore Seismic Survey Begin?

PG&E plans to undertake the final, offshore high-energy study as soon as it obtains all necessary permits from federal, state and local agencies, including the State Lands Commission, California Coastal Commission and County of San Luis Obispo.

Under a recent proposal submitted to the California Coastal Commission, the first phase of the high-energy offshore seismic survey will be conducted from mid-November through December of 2012 (PDF, 3.1 MB), and the second during the same time period in 2013 (PDF, 3.1 MB). This is the time of year in which there are the fewest number of marine mammals located off the Central Coast. It is also a low fish larvae period.

The first survey is expected to last approximately 12 days (9 days of active survey) and will focus on studying portions of the Hosgri, Los Osos and Shoreline fault zones in the region of Estero Bay. The survey will not overlap into the Point Buchon Marine Protected Area.

After completion of the first survey area this year, PG&E will evaluate the results, as well as the effectiveness of the technology and the marine life mitigation programs. PG&E will then share the results with the state-created Independent Peer Review Panel (IPRP) and seek their input as the company determines how to proceed with the remaining surveys.

How Does It Work?

PG&E will use the research vessel R/V Marcus Langseth, which is owned by the National Science Foundation, to conduct the high-energy offshore testing. The Foundation uses the vessel to perform similar research around the world.

To conduct the work (PDF, 394 KB), equipment onboard the vessel will generate sound waves that will be directed toward the ocean bottom. An array of buoys towed by the vessel will capture the sound waves as they reflect back to the surface. The data recorded will be used to create a detailed three-dimensional map of seismic faults.

This information from the study will help further define the ground motions that faults in the region are capable of producing, which PG&E will use as part of its ongoing work to continually assess and validate the seismic design of the plant. The data will also be used to support a federal requirement for an updated seismic risk evaluation following the Fukushima Daiichi power plant tragedy.

What Are the Potential Impacts to the Environment?

Recent findings by federal agencies, which regulate the protection of marine mammals, have projected that the high-energy offshore research may cause a temporary disturbance -- but no long-term impacts -- to marine mammals and fish in the survey areas.

Similar seismic research is performed around the world and no adverse, long-term impacts to marine life have been observed. Currently, more than 20 similar surveys are taking place in waters near the coasts of the United States and dozens are happening elsewhere globally.

PG&E is committed to conducting the work safely and in a manner that results in the least impact to the environment through implementing numerous marine life protective measures (PDF, 394 KB) and monitoring programs.

What Are the Potential Impacts to Commercial Fishing?

The sound waves emitted from the research vessel may temporarily cause fish in an active survey area to change their behavior, migratory and movement patterns. Fish that are displaced are expected to return within a few days after the sound source ceases.

While the research is underway, commercial boat traffic will be encouraged to remain out of the active survey area and at least at several miles away (two miles ahead, 3 miles to the sides, 5.5 miles to the rear) from the research vessel. PG&E recognizes this could have a short-term impact on local fish catches and is engaged in discussions with representatives of local commercial fishermen to find a fair and equitable compensation solution.

Will Beaches be Closed During the High Energy Seismic Survey?

PG&E is not recommending that authorities close beaches during the high-energy seismic survey and is working closely with regulatory agencies to ensure that marine recreationists (surfers, swimmers, SCUBA divers) are aware of when a specific survey area will be studied, and any precautions they should take.

PG&E will post clear and visible public safety notifications at beach parking lots, beach access trails, and ocean access points near active survey areas. These notifications will provide the anticipated survey duration along with warnings regarding the anticipated exposure to elevated sound levels in nearshore waters. The notifications will also include contact information for PG&E personnel who can be consulted for additional information regarding the scheduling and location of survey activities. All notifications will be in English and Spanish.

While the survey is underway, sound levels generated at the survey vessel are expected to reach 250 decibels (dB) and will diminish as they travel away from the sound source. Survey models have shown that a sound level of approximately 160 dB could potentially reach some shoreline areas during the 2012 survey. These areas include PG&E lands north of Diablo Canyon Power Plant, a portion of Montana de Oro State Park, a portion of the Morro Bay Sandspit, and an area northwest of Cayucos. The 160 dB level is a conservative estimate and does not take into account physical features such as rocks and kelp that would absorb the sound before it reaches the shoreline, or the existing sound levels generated by ocean waves. Naturally occurring noise levels at beach surf zones reach approximately 145 dB. U.S. Navy research has shown that sounds generated from the survey would not have a harmful impact on surfers and swimmers as a person would have to be submerged and continuously exposed to 154 dB or higher for 15 minutes before experiencing harmful impacts.

To prevent potential impacts to SCUBA divers, dive boats will be required to remain out of the active survey area. In addition, all vessels, including dive boats, will need to maintain several miles distance (two miles ahead, 3 miles to the sides, 5.5 miles to the rear) from the research vessel. SCUBA diving will not be allowed in an active survey area.

Will Local Businesses be Impacted by the Work?

While the research is underway, commercial boat traffic and SCUBA diving operators will be encouraged to remain out of the active survey area and at least several miles away (two miles ahead, 3 miles to the sides, 5.5 miles to the rear) from the research vessel. PG&E recommends these buffer zones to avoid possible entanglement with the survey equipment and to prevent divers’ potential exposure to the undersea sound waves generated by the survey.

Access to marine ports and harbors will not be impacted by the work and inactive survey areas will remain open to traffic.

PG&E understands that these short-term restrictions, once in place, may affect local businesses. To minimize economic impacts, PG&E has an established claims process in place for all parties who believe that they have been adversely impacted by the work. Claims related to the high-energy offshore seismic survey will be fast-tracked and the process will be managed locally.

How Can I Get More Information?

PG&E is committed to keeping the public informed of project activities and to providing information to interested parties as the surveys progress. PG&E has created a registry to collect names and contact information in order to contact people who would like more information about the project. You can enroll electronically or call toll free 1-855-265-5927. PG&E is committed to your data privacy and will not share or distribute your contact information for any purpose beyond the scope of this project.

PG&E Explains the Diablo Canyon Seismic Studies

Learn more about PG&E's advanced seismic research program by viewing this video.

How the 3D High-Energy Survey Works

How the 3D High-Energy Survey Works

Seismic Survey Safety

PG&E is committed to conducting the 3-D high-energy offshore seismic study safely and in a manner that results in the least impact to the environment through implementing numerous marine mammal protection measures.

Seismic Survey Safety
  • Impacts will be minimized through implementation of a Marine Wildlife Contingency Plan (MWCP).
  • The MWCP includes stationing trained Protected Species Observers (PSOs) on board the survey and support vessels to watch for and alert operators to the presence of marine mammals.
  • The National Marine Fisheries Service (NMFS) and PG&E will also have PSOs in an airplane to conduct aerial surveys for density/distribution of marine mammals approximately one week prior to and during the survey. The survey area could be adjusted based on the results of the aerial survey.
  • Acoustical and infrared equipment on the research vessel will monitor for marine mammals.
  • Before a survey begins, only one air gun will sound at a low-level to warn marine life, before gradually ramping up to full power.
  • The air gun sound source will be managed based on proximity of marine mammals to the survey vessel.
  • While conducting the survey, a 180 dB exclusion zone and a larger 160 dB safety zone will be maintained around the vessel to prevent potential impacts to marine mammals.
  • If a marine mammal appears likely to enter the 180 dB exclusion zone (the 1.2 mile ring around the vessel) then protective actions will be taken, including powering down the sounding equipment or a complete shutdown and suspension of work.
  • Marine mammals that enter the larger 160 dB safety zone, which extends to 3.8 miles around the vessel, will be monitored by trained observers and either changes in vessel speed or course will be taken to avoid them. These zones were established in consultation with the NMFS.
  • The survey time period of November through December is the time of year in which there are the fewest number of marine mammals off the Central Coast. It is also a low fish larvae period.

Download PDF (PDF, 394 KB)

Seismic Survey Safety & Monitoring

PG&E is committed to conducting the 3-D high-energy offshore seismic study safely and in an environmentally responsible manner.

Learn about the safety measures

Learn about the marine monitoring program

Learn about SSHAC (Senior Seismic Hazard Analysis Committee)

Stay Up-to-Date on the 3D High-Energy Survey

PG&E is committed to keeping the public informed of project activities and to providing information to interested parties as these surveys progress.

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