Shaky ground
Bay Area residents take the term “earthquake” very personally. Many of us remember the epic ground-shaking of the 1989 Loma Prieta quake, and no matter how many teams of engineers tell us not to, we worry about being anywhere near the sinking Millennium Tower when the next big one hits. Historically, a significant before-and-after are marked by the 1906 quake and the subsequent fires that destroyed most of San Francisco. The slow reboot that followed set down the structural template upon which our contemporary metropolis is built. We know earthquakes as terrifying yet trans-
formational events in which geological history abruptly rearranges human history. And we are in awe.
How, exactly, do earthquakes work? In his entertaining and enlightening book, “The Great Quake: How the Biggest Earthquake in North America Changed Our Understanding of the Planet,” Henry Fountain tells the story of what is sometimes called “Alaska’s Good Friday Earthquake.” On March 27, 1964, a 9.2-magnitude quake shook the state to its core, both literally and metaphorically. Partly because of Alaska’s sparse population, the overall death toll was only 131. It speaks to the power of the quake, however, that several of those who died were victims as far south as Oregon and California — one fatality due to gigantic waves in Bolinas Bay. The Alaska quake is impressive in and of itself. The way it deployed also shed new light on how we understand both earthquakes and the whole tectonic framework in which they occur.
Fountain focuses much of his narrative on George Plafker, a U.S. Geological Survey scientist, who teased out lessons from the Good Friday quake to help establish fundamental concepts about the deep workings of the Earth. An unassuming technician who spent eight years of his childhood in a Brooklyn orphanage, Plafker is an everyman distinguished by curiosity and persistence. His interest in rocks and what makes them move got an early boost from a geology professor at Brooklyn College who took his students on field trips around the New York metropolitan area.
The story of Plafker’s path to the Alaska quake is interspersed with a narrative explanation of how science has grappled with the shapes and placement of the continents and how they got that way. As early as 1911, Alfred Wegener put forward an idea that came to be known as “continental drift,” suggesting that though we think of Earth’s largest land masses as stationary, in fact they are on the move. Wegener opined that the Earth was once comprised of a single supercontinent, a giant land mass he called Pangaea. About 175 million years ago, Pangaea started to break up. As gigantic land masses separated, their leading edges crumpled and formed mountains. Wegener’s idea was reviled, partly because he was not a professional geologist, and because he did not identify a plausible mechanism by which the continents travel. Well after Wegener’s death, the phenomenon of seafloor spreading provided an explanation — hot rock welling up from Earth’s mantle creates a conveyor belt upon which continents ride.
In contrast to the painstaking process by which science arrives at its certainties, an earthquake takes just a few minutes to reorder reality. Fountain sets the scene for an abrupt wakeup call, and his description of how it unfolds is gripping. Take Bob Atwood’s experience. The publisher of the Anchorage Times was practicing the trumpet that fateful afternoon. The motion of the Earth as the event started was gentle at first, then “Alaskans began to see and hear things they’d never seen or heard before.” Shock waves tore through pavement and buildings, and the land resembled a stormy sea. A deep roar engulfed the atmosphere. Atwood escaped his house, then watched it essentially explode. “Suddenly a crevasse opened beneath his feet, and he was falling.” He notices that tree stumps, fence posts and boulder-size chunks of frozen soil are falling with him. Miraculously, he lands in sand. He is still holding his trumpet. Then he observes his neighbor’s house, sliding toward him.
The day after the quake, Plafker flew to Alaska. Perusing thousands of devastated miles, he looked in vain for evidence of what must be a huge fault responsible for such a rupture. Frank Press, the head of the seismology lab at the California Institute of Technology, concluded that the quake was caused by a “dipslip” fault, in which one block of crust moves past another vertically. Plafker was unknown compared to the highly accomplished Press, but he disagreed. Plafker thought that rather the quake had been caused by a “thrust” fault. Pressure mounts where the oceanic crust of the Earth slides under the continental crust, building friction until the strain becomes so great that there is a “sudden release of an enormous amount of stored up energy.”
Press eventually conceded that Plafker was right; and the Alaskan quake was eventually credited to a “megathrust” fault. It demonstrated Wegener’s essential correctness and helped quantify the synthesis of Earth science today known as plate tectonics. All it took was years and years of careful consideration and a fateful five minutes.
Mary Ellen Hannibal is the author of “Citizen Scientist: Searching for Heroes and Hope in an Age of Extinction,” now in paperback. Email: books@sfchronicle.com