U.S. Geological Survey Seismologist ‘Not Expecting Anything Strikingly New’ from $64M PG&E Central Coast Seismic Test

U.S. Geological Survey

PG&E’s $64-million ratepayer-funded Central Coastal California Seismic Imaging Project may yield some interesting geologic images, but according to a U.S. Geological Survey seismologist the controversial high-energy seismic test will likely be used to update computer models of the earthquake fault system around and under the Diablo Canyon Nuclear Power Plant in Avila Beach, rather than to upgrade the plant itself.

Updating computer models may prove to be the sole benefit of the test to public safety at Diablo Canyon; public safety was the overriding consideration deployed by PG&E and permitting agencies to expedite the permitting process without adequate review of the test’s real consequences and ultimate costs. In addition to the manner that test results will actually be applied, the test, according to a second U.S. Geophysical Survey seismologist, is not likely to reveal critical new data such as fault length, rate of slippage or past frequency of eruptions.

“We do have a pretty good idea where the faults are from ‘low energy’ seismic imaging, locations of small earthquakes, and gravity and magnetic studies,” Jeanne Hardebeck, research seismologist for the U.S. Geological Survey in Menlo Park, California, told The ROCK. “The new studies, if successful, could add some new information that could refine our models of where the faults are and how they connect, but we’re not expecting anything strikingly new.”

The USGS is not participating in the upcoming PG&E survey, which begins off the Central Coast on November 1 and runs through the end of the year. A seismic review is state-mandated following Assembly Bill AB 1632, and the USGS is a federal agency.

Ms. Hardebeck, who is credited with recognizing the discovery of the Shoreline Fault in 2008 using PG&E and USGS data, remarked in the San Francisco Chronicle/SFGate last July that it was logical to assume that the Hosgri and Shoreline faults are connected and could place a magnitude 7.2 earthquake close to the plant.

“With the data I’m looking at, it actually doesn’t make sense to think of these faults as not connecting to each other,” Ms. Hardebeck said. “An interpretation that says they don’t connect doesn’t seem to fit with the observations that we have.”

Ms. Hardebeck points out that a magnitude 7.2 quake on the combined faults would cause greater ground-shaking at the nuclear plant than a magnitude 7.5 quake 3 miles offshore on the Hosgri Fault acting alone.
However, if the faults act together with others in the region, which is what some scientists suspect, it could produce an earthquake more powerful than the plant was originally built to withstand.

In the same July 2011 Chronicle article, U.S. Geological Survey scientist Sam Johnson described whether the fault lines are actually longer than previously known – and “there could be one long rupture” – as a “hot-potato issue” in seismology circles. PG&E’s 3D high-energy test encompasses 540 square miles off the Central Coast, yet does not take into account the actual length of the fault lines, data that PG&E and USGS have collected through the California Seafloor Mapping Program.

One USGS scenario shows the Hosgri Fault extending 250 miles from Point Conception to Bolinas, just beyond San Francisco, 145 miles longer than its officially published length of 105 miles. The longer the length of the Hosgri, according to Mr. Johnson, the more likely it could connect with other faults to the north of the plant to produce “close to an 8.0” earthquake. Diablo Canyon was constructed to withstand ground-shaking from a 7.5 earthquake on the Hosgri, three miles off shore. This scenario might elevate concerns.

State Senator Sam Blakeslee, who has a doctorate in seismic studies and authored AB 1632 requiring a seismological review of fault lines prior to the relicensing of Diablo Canyon.”If it’s reasonable to infer that a much larger earthquake could occur but the studies come back inconclusive,” he said last year, “the NRC has one of two choices: to plan as though it could or to ignore that possibility because it couldn’t be proven.”

Apparently fully aware of high-energy seismic test impacts that threaten the existence of Central Coast marine life and local economics based around the environment, sea life and fishing, Blakeslee’s two options were at the time: plan for a “much larger earthquake” or “ignore it.” Both “choices” could and should have been addressed prior to and without a costly, unnecessary test that causes damages likely to approach or exceed the final cost of the test.

At the same time, the unpredictability of large magnitude earthquakes and Diablo Canyon’s location on a bluff and proximity to fault lines will not make the plant any safer as a result of the test than it was before the test, before an unprecedented high-decibel sonic assault is unleashed on any and all sea life every day, 250 decibels every 15 seconds for two months. According to National Resources Defense Council research: “Sound travels outward so widely as to significantly raise noise levels literally thousands of miles away.”

In a September 18 response to any inquiry from Los Osos activist Al Barrow regarding a “less destructive methodology” than high-energy, Ms. Hardebeck wrote about alternative testing options. “Seismic surveys are only one of many ways to image faults,” she wrote. “GPS data doesn’t tell us where faults are, but it can tell us how fast they are moving, and therefore how often they have large earthquakes.”

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San Francisco Chronicle link: http://www.sfgate.com/news/article/PG-E-USGS-disagree-on-Diablo-Canyon-fault-danger-2354326.php