Long before Fukushima there was one earthquake that counted the most for the Diablo Canyon nuclear plant, and that earthquake has been kicked around now for half a century. Today I received a copy of that much discussed but rarely seen report on Diablo Canyon seismicity written by Hugo Benioff and Stewart Smith, which I include in full later in this post. True, the findings date to the mid 1960s when many things were not known. As Smith put it to me in retrospect:
In the Geological Sciences we were still puzzled over the worldwide distribution of seismicity because the plate tectonic model had yet to be discovered. Benioff had much earlier recognized dipping zones of earthquakes, which we now call subduction zones, off the coast of South America and elsewhere, but there was not yet an overarching theory to explain how these were related to features like the San Andreas, which we now recognize as transform fault necessary to account for the plate motion produced by subduction. As I recall this was an era in which Clarence Allen at Caltech had pronounced that, based on the widespread nature of aftershocks in Chile, a large earthquake could occur anywhere in California. I don't recall the reference, but I do remember the slide he would show where he overlaid the aftershocks of the Chile earthquake of 1960 on a map of California. The entire state was filled with earthquakes.
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| Victor Hugo Benioff |
But the Benioff-Smith report conveys remarkably sound judgment in many respects, notably in its conclusion that the Diablo site is subject to a magnitude 6 3/4 earthquake occurring directly beneath the plant. The effects of exactly this type of event have just been presented by PG&E and its SSHAC committee to the NRC, and they are worth examining, contradicting as they do key elements of the Benioff-Smith conclusion and design recommendation. We can easily and will examine this proposition later by using various online tools to estimate ground shaking at the Diablo Site and in a manner that should be understandable to any bright high school student.
The key finding of the Benioff-Smith report comes in the last paragraph of the report:
