Cascadia's Fault - Jerry Thompson [36]
All eyes were on the immediate tragedy and its aftermath. The notion of an Alaska-size quake from a subduction zone just twenty or thirty miles (30–50 km) off the California coast struck no fear in the hearts of Eureka, Arcata, or the other small communities of northern California. Only those scientists who’d read—and were convinced by—the latest research realized what the Alaska story meant to the rest of the coast.
Many frontline scientists themselves were still at odds over what to make of plate tectonics. In February 1965, almost a year after the biggest known earthquake in North American history, Frank Press, the distinguished seismologist at Caltech, published a paper describing the fault that had wrecked the Alaska coast as a steep, vertical crack in the ground, similar to the San Andreas. Four months later George Plafker, the young geologist who did the muddy-boot work of measuring and documenting the aftermath, published his own paper saying just the opposite: that the fault ran at a shallow angle from the sea floor underneath the continental landmass. Plafker thus cast his vote in favor of tectonic theory while Press, the established authority, took a more cautious position—and his was still the majority view.
A nearly identical disagreement about the Mendocino Triple Junction arose three years later. A team of scientists at the University of California seismology lab in Berkeley released a paper in 1968 suggesting the San Andreas did indeed extend out to sea from Cape Mendocino and was in the process of cracking its way toward Alaska. Searching through seismograms for clusters of quakes, they discovered that Cape Mendocino was trembling at a rate “two to three times that of the combined central California clusters,” which seemed to confirm that those broken slabs of sea floor were on the move, just as Tuzo Wilson had predicted they would be.
Bruce Bolt and his colleagues at Berkeley calculated a series of fault plane solutions and decided that many of the smaller tremors were generated by cracks running northwesterly through the Gorda plate toward Alaska—not northeasterly, as you might expect if the Gorda plate were being pushed underneath the California coast by seafloor spreading. Essentially Bolt and his team believed the region was “dominated tectonically by the San Andreas.” No mention in their paper of spreading ridges offshore, low-angle faults, or pieces of oceanic crust getting stuck underneath the continent. The Alaska threat did not apply to California in their view.
Then along came Eli Silver from the U.S. Geological Survey in Menlo Park. In 1971 he wrote a new paper on the tectonics of the Mendocino Triple Junction and came to the opposite conclusion from Bolt. Recall that there are always two possible answers to a fault plane calculation—one being ninety degrees different from the other. While Bolt chose the northwesterly solution, Silver was sure the northeastern vector (and tectonic theory) was correct.
Meantime, as if anyone needed a reminder, the San Andreas showed once again that it still had the power to shock, wreak havoc, and dominate the attention of scientists and the general public. On February 9, 1971, the magnitude 6.6 Sylmar earthquake struck the San Fernando Valley, killing sixty-five people and rattling Los Angeles emergency planners, police, and firefighters like nothing had in years. Seeing two hospitals (one of them brand new) and a dozen freeway bridges collapse prompted state politicians to pass a new law (the Alquist-Priolo Earthquake Fault Zoning Act) that would tighten building codes and severely restrict construction of residential buildings and critical infrastructure on or near any active fracture zone in California.
Only a few years later, two geologists hiking the north woods of the California coast would quietly shift the focus back to the atomic power plant at Eureka. Gary Carver, a freshly minted professor at nearby Humboldt State University, and Tom Stephens, one of his senior