Cascadia's Fault - Jerry Thompson [37]
The Simpson Timber Company had kept hundreds of miles of access roads closed to the public during the 1950s, ’60s, and ’70s while they logged off huge stands of old-growth redwood forest. None of the land had been geologically mapped and Carver and Stephens didn’t quite know what to expect. “We were able to go back in where geologists hadn’t been for a very long time,” Carver told me.
Now, with the big trees gone, the ground was nearly naked and rock formations were easier to see. Still, Carver and Stephens had to hike for miles and miles along steep switchbacks, mapping and following a web of fractures from the mountains all the way west and downhill to the intertidal and beach zones along the coast. They noticed a distinctive angularity, what they called a “rhombohedral fracture” pattern, which to a non-geologist’s untrained eye would look like nothing more than “tiny little cracks in the sand” of cutbanks sliced through the wilderness by road builders for the logging crews.
This rhombohedral pattern, Carver explained, was how faults propagate through unconsolidated sand deposits. This was loosely packed sand left behind when this part of the coast was under water, a wedge of ocean sediment that had been shoved against the continent and now stood well above the high-tide line. “Instead of a nice, clean, one-plane fault in which two pieces of the earth’s crust move past each other, it becomes hundreds or thousands of little tiny faults all closely spaced together,” he elaborated. “I thought this was really neat.”
Each of the fractures Carver and Stephens found cut through geologically young terrain, suggesting the cracks were relatively recent. That meant whatever tectonic force had caused the fractures might still be an ongoing threat. Carver was pretty sure the rhombohedral fractures had been caused by plate convergence and compression. While none of the individual cracks had a huge amount of movement, taken as a whole the offset was significant.
“We realized that these little tiny fractures we were seeing in many places were parts of faults that had very large amounts of displacement on them,” said Carver. The displacement added up to several miles in total. “And again—you’re sittin’ right there on the edge of the mapped subduction zone and you see those big folds in young sediment,” said Carver, “and you can’t help but think that that subduction zone is still active.” All of this within a few miles of the nuclear plant at Humboldt Bay.
That’s when Carver decided to fly north to Alaska for a first-hand look at what had happened there. He needed to “see what a big earthquake looked like” in all its mangled glory so that he could better understand what he was seeing on the ground in California.
CHAPTER 7
Proving the Doubters Wrong: The Chile Connection
Gary Carver spent an entire summer in Alaska looking at the aftermath of subduction. He flew the entire length of the ’64 rupture, every mile of broken shoreline. He also met George Plafker, who was more convinced than ever that the primary fault that had caused the beaches and bays to heave, buckle, and subside could not have been vertical. Plafker had recently returned from Chile and was eager to tell anyone who’d listen that the two biggest earthquakes in recorded history had caused exactly the same kinds of physical damage to the landscape.
Not only that, but some very prominent senior scientists were apparently coming around to Plafker’s point of view. Frank Press, who had so famously disagreed about the angle of the fault, sat in the audience at the 1968 meeting of the American Geophysical Union in Washington, DC, and listened to Plafker’s presentation of his paper on Alaska. The main theme of that year’s convention was “The New Plate Tectonics,” and here was Plafker telling the science establishment that the Alaska quake had been caused by