Cascadia's Fault by Jerry Thompson Read Free Book Online

shockwaves with each higher whole number on the scale. If a magnitude 4 caused rocks to vibrate and move less than half an inch (1 cm), a magnitude 5 would cause them to move four inches (10 cm). Some studies have estimated that this tenfold increase in the amplitude of the shockwaves would require thirty-two times more energy. So a magnitude 9 would generate thirty-two times more energy than a magnitude 8.
    The Mexico City quake was an 8.1 and the 1960 Chilean disaster was a 9.5, the largest temblor ever recorded by modern instruments. That means the Chilean rupture generated more than thirty-two times the energy of the Mexico City event. And here was William Bakun of the USGS telling us to expect the same in the Pacific Northwest.
    We had come to Menlo Park primarily because Bakun and his colleague Allan Lindh had recently launched the first high-profile earthquake prediction experiment on U.S. soil. The Chinese and Japanese had
both been running prediction studies for several years already, but given their spotty results and the controversial nature of spending money to forecast disaster, this was a bold leap for the USGS. As a journalist I figured the first thing people living in any hazard zone would want to know was: when will the Big One finally happen? Now some of America’s top scientists were trying to provide an answer.
    â€œWe can predict earthquakes, in one sense,” Bakun said, cautiously. “We can identify sections of plate boundaries that will eventually fail in large, damaging earthquakes.” Figuring out where the San Andreas fault might break again, or being pretty sure that the Juan de Fuca plate will rip loose from the North America plate some day, sounded like important science to me, although I’m pretty sure that’s not what most people think of as prediction. Bakun agreed. “We still do not know how to predict earthquakes on a short-term basis. That has turned out to be a very difficult problem, and it’s a focus of our ongoing research.”
    Bakun’s coauthor in the prediction study, seismologist Allan Lindh, told us they were studying a stretch of the San Andreas near the farming town of Parkfield, California, that had ruptured five times since 1857—each event a magnitude 6 temblor that seemed nearly identical to the one that came before, as if the same punch were being thrown over and over again. Bakun and Lindh had convinced themselves the next in this series of “characteristic earthquakes” was due in about three years. According to their calculations, the fault would build up enough stress to break again as early as January 1988.
    In August 1985, only a few months before our visit, Bakun and Lindh published the first official seismic prediction ever issued by the USGS: “The next characteristic Parkfield earthquake should occur before 1993.” Even with a five-year fudge factor, they had stuck their necks out by putting the prediction in writing in Science, one of the most prestigious and high-profile research publications in the world.
    Like Bakun, Lindh seemed to be a cautious man. Still, there was enthusiasm in his voice as he talked about trying to trim the fudge
factor and “narrow down the time from a few years to months, to a few days.” He told us, “I think we’ve got a fighting chance,” asserting that the way to refine the prediction was to concentrate as many instruments as possible along one small segment of the fault—the same fifteen-mile (25 km) rupture zone that had moved in each of the previous Parkfield punches—and monitor every little creep and twitch in the earth, day and night, until the next rupture. With luck, they might spot some kind of precursor that would allow them to issue a warning to the public.
    When we wrapped the USGS shoot late that afternoon, my team and I drove four hours south on Highway 101 from Menlo Park, through the rush hour of San José, to a wine-country town