Cascadia's Fault - Jerry Thompson [27]
Plotting his elevation numbers on a map, Plafker also noticed an invisible line of “zero change” in the level of land, approximately parallel to the south coast mountain ranges and to the deep Aleutian Trench offshore. On the seaward side of this invisible line, the land had been raised; on the landward side it had dropped down. “What I was doing was just trying to get some feeling for whether these areas of uplifted and subsided ground might be pointing to a fault in between them,” he told me.
If there was a hidden crack in the earth, it seemed odd that heaving up and dropping down—especially on a scale as grand as this—could have happened without breaking the surface. How could so much land be jacked up or slumped with no visible fracture line? And yet “we never could see the fault,” he said, and that made the Alaska mystery all the more fascinating.
In numerous places he saw the “squeezing up of the rocks,” which he likened to a crumpled fender. It all looked very different from the kinds of surface damage he’d seen when plates slid past each other along a fault like the San Andreas. In California the earth was fractured vertically—and it was plain to see—but in Alaska the rocks were being folded up and shortened. Or stretched horizontally like taffy.
The essential unknown of the Good Friday rupture—the true nature of the fault—needed an explanation, so Plafker and his colleagues spent months living on a converted river tugboat, prowling the shore in small skiffs, measuring rocks and crunching numbers trying to make sense of what they’d found. Their data logs were so chock-full of bewildering new information it would take until June the following year to get it organized and published.
To make the job more challenging, Plafker, a relatively young scientist who had not yet earned his PhD, was preparing a report about earthquakes—not his chosen specialty. He was a geologist who’d spent most of his career up to that point mapping rock formations, searching for oil and other natural resources. He was not trained as a seismologist, yet here he was writing about an unseen fault that had behaved contrary to what most experts in the field were familiar with. This invisible crack along the Alaska coast appeared so unlike the San Andreas that the facts and figures Plafker came back with beggared belief. And got him into a bit of hot water.
The new science that would eventually explain what happened in Alaska—the revolution in geology now known as plate tectonics—was in mid-evolution in 1964. The controversial theories had not been refined, tested, or accepted. “They were still just barely getting to it at the time of the earthquake,” recalled Plafker. Strange as it may seem today, there was no broad consensus then on how mountains and volcanoes were formed or what kinds of forces generated earth tremors. Geophysicists didn’t even know for sure whether faults caused earthquakes or, the other way around, earthquakes caused faults. Was the earth’s surface cooling and shrinking and cracking? Or was it expanding and cracking because of radioactive heat from the deep interior of the planet? All these big ideas were still very much in play.
When I phoned him in 2009 to talk about the turmoil of the times, it was hard for Plafker to remember after so many years exactly what he knew when he flew north from Seattle that day in 1964, but one name did stand out. Hugo Benioff, who in the 1930s had designed and built the most sensitive earthquake detection equipment in use, was one of the three wise men who pioneered the young science of seismology at the California Institute of Technology (Caltech) in Pasadena. Benioff had written a classic series of papers between 1949 and 1954 that drew the first hazy picture of big slabs of the ocean floor thrusting underneath the margins of the Pacific Rim.
Benioff borrowed the voluminous and detailed charts of worldwide seismic data compiled by