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Seismic study loses air over wildlife concerns

Bruce Gibson argues for the use state-of-the-art seismic survey techniques.

screenshot from California Coastal Commission live webcast

A California regulatory board on 14 November denied a key permit for a proposed study of under-sea faults near the Diablo Canyon nuclear power plant in San Luis Obispo County. The plant’s owners, San Francisco–based Pacific Gas and Electric Company (PG&E), had designed the project to aid the state in re-evaluating earthquake risks to California’s two nuclear facilities following the Fukushima Daiichi disaster in March 2011.

The California Coastal Commission reached a unanimous decision after hearing hours of testimony from PG&E, interest groups and concerned citizens. Environmental groups such as the Natural Resources Defense Council (NRDC), based in New York City, argued that marine wildlife would be harmed by the use of high-energy seismic reflection — a technique that maps geological structures in three dimensions by shooting intense sound waves into the ocean and measuring their echoes off of geological features beneath the sea floor. The sound blasts, which measure 230–252 decibels at the air gun source, can penetrate 10–15 kilometres into the Earth.

In its own staff report, the California Coastal Commission estimated that more than 7,000 marine mammals — including several whale species, harbour porpoises and sea otters — would be disrupted by the study. “There will be impacts,” acknowledged Mark Krause, director of state agency relations for PG&E. “We believe we’ve mitigated them to the degree feasible.” In recent months, the company had revised the proposal to reduce the survey area and included additional wildlife monitoring efforts.

PG&E has argued that high-energy testing could provide the most detailed maps yet of a complex network of offshore faults near the plant, including the Hosgri Fault, which lies about three miles to the west. But the commission remained unconvinced that the possible benefits of the project outweighed the costs.

“We know that there is potential for very significant marine resource impacts here,” said Charles Lester, the commission’s executive director. “We don’t feel the case has been made that this particular test at this time is needed.”

The commission urged the company to finish analysing other seismic data it has collected using onshore and low-energy offshore techniques in recent years — data that many opponents say could obviate the high-energy tests.

Still, other critics, such as Bruce Gibson, a former geophysicist and a current county supervisor in San Luis Obispo, want to see the high-energy studies carried out but using more sophisticated technology that might collect data faster and with less environmental disruption.

If the company decides to submit a revised plan, it may still need to convince commissioners that the information gleaned from high-energy seismic tests would have practical value.

In her closing comments, commissioner Jana Zimmer questioned whether more detailed maps of the surrounding faults could be used to  improve the safety of the plant, which is currently designed to withstand a 7.5-magnitude quake.

“If we assume that there is a possibility of a disastrous quake — an 8.5 or 9.0 quake — are there design fixes, are there technologies that we know about that are available… that it would be able to withstand such a quake?”  She said that she hasn’t received a satisfactory answer from the company.

Even if not for safety considerations, some scientists saw the project as an opportunity to collect crucial information about tectonic interactions between the Pacific and North American plates, which create lateral motion along several ‘strike-slip’ faults in the region.

“Strike-slip systems are not straight lines on a map and in 3D they’re not simple planes. To understand their complexity they need to be imaged, and this is an opportunity to image one in great detail,” Art Lerner-Lam, deputy director of the Lamont-Doherty Earth Observatory of Columbia University in Palisades, New York, told Nature.

PG&E had hoped to enlist scientists from the observatory to conduct the seismic research using the National Science Foundation–owned research vessel Marcus G. Langseth. If chosen, the scientists would have made the project data publicly available.

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