Cascadia's Fault - Jerry Thompson [40]
Roughly a year later, in July 1976, when the reactor was shut down for routine refueling, the seismic safety questions were red-flagged by the Nuclear Regulatory Commission. The NRC decided to keep the plant closed until the Little Salmon fault and the new system of fractures discovered by Gary Carver and Tom Stephens could be checked and the seismic hazard issues dealt with.
PG&E hired several consulting firms to conduct field studies to find out whether any of the faults were still active. A sixteen-station array of seismographs was installed in the surrounding mountains and along the northern California coast to get a more detailed picture of all the tectonic motion. In addition, the NRC decided to send its own team of scientists into the field to follow up on the work done by Carver and Stephens.
They created a timeline of earthquakes in the region. With backhoes they dug trenches across the Little Salmon and Mad River faults for close-up looks at where and how often the various layers of soil and rock below ground had been torn apart. Taking samples of woody debris, dead plants, and the remains of tiny sea creatures contained in the layers disrupted by quakes, they used radiocarbon dating to figure out when the ruptures had happened.
In the fall of 1980 the geologists concluded that the Little Salmon fault was indeed active and that it probably ran underneath or very close beside the reactor. The bottom line according to Woodward-Clyde Consultants, hired by PG&E, was that the seismic issues could be dealt with but the job would be neither cheap nor easy.
At this point two other factors may have entered the equation for Pacific Gas and Electric. On March 28, 1979, while the Woodward-Clyde team was still documenting the gritty details of the Mad River area and how it might affect the reactor at Humboldt Bay, things went alarmingly wrong at a nuclear power station called Three Mile Island in Pennsylvania. A relief valve got stuck open, allowing large amounts of radioactive coolant to be released into the atmosphere. The reactor core overheated and barely survived a partial meltdown.
The accident, while not as catastrophic as it might have been, helped turn the tide of public opinion against nuclear power. By some masterstroke of luck or serendipity, a Hollywood movie called The China Syndrome had been released only twelve days before the Three Mile Island accident. The eerily prescient film became an instant box office hit and probably did much to seal the fate of nuclear power in the United States. After months of investigation and analysis, the Nuclear Regulatory Commission issued a new set of far more stringent safety rules that would apply to all reactors, including the one at Humboldt Bay.
Add to this the legal, political, and financial implications of California’s own new seismic zoning law, the Alquist-Priolo Earthquake Fault Zoning Act, which was passed in the aftermath of the Sylmar temblor, and the job of retrofitting and upgrading the reactor at Humboldt Bay became too expensive to be economically feasible for PG&E. Four years later the utility applied for permission to decommission the reactor permanently.
In the aftermath, an official report to the U.S. Geological Survey described the twenty-five-mile (40 km) Little Salmon fault as “part of a broad, compressional fold and thrust belt developed in the accretionary wedge above the Cascadia subduction zone.” An accretionary wedge is formed by the sediment and pieces of seafloor crust piled up in a trench where two tectonic plates collide. Think of the North American continent drifting west like a snowplow across the sea floor, scraping up muck and compressing it into rock.
In most cases the wedge