Cascadia's Fault - Jerry Thompson [15]
First, I asked myself, who else knew there was even a fifty–fifty chance of a magnitude 8 rupture? Probably nobody except the scientists. Then it occurred to me—okay, so the senior seismologist at the Canadian government’s West Coast geoscience laboratory is a cautious man who doesn’t want to alarm the public without reasonable and probable cause. I understood that. Yet now, in the aftermath of Mexico City, he was apparently ready to raise the biggest, reddest warning flag I’d ever seen.
“Now you’re saying it?” I prompted.
Weichert took the plunge: “We’re saying yes, we have to come to grips with this problem. The chance has increased, in our minds, from a fifty–fifty chance to something like a seventy–thirty chance for the earthquake to happen within, say, the next two hundred years.”
As a scientist, he really couldn’t say for sure when the megathrust might happen—two hundred years from now, or tonight—so Weichert had erred on the side of caution. That’s what responsible government scientists do. Kaufman and I, however, figured Weichert, Rogers, and Adams had given us a clear signal that the risk level was sufficiently high to justify front-page treatment of the issue.
On Sunday, November 3, 1985, I flew from Vancouver to San Francisco en route to the U.S. Geological Survey laboratory at Menlo Park, California. First thing Monday morning we shot an interview with USGS seismologist William Bakun, who not only reinforced what the Canadian team had told us the previous week but made an even more ominous prediction. He said the Juan de Fuca plate could generate a disaster even larger than the one in Mexico.
“We have to take seriously the possibility that a great earthquake—a very great earthquake, such as the 1960 Chilean earthquake—might occur along the Washington, Oregon, and British Columbia coast,” said Bakun. “We’re talking about as big an earthquake as has occurred in historic time—in the world.”
Knowing almost nothing about what happened in Chile, twenty-five years earlier, I again asked for clarification. “Where would that be on the Richter scale?”
“Off it,” he laughed weakly, and then quickly followed with an explanation. A moderate earthquake is defined as magnitude 5.0 to 5.9; strong is 6.0 to 6.9; major is 7.0 to 7.9; and a great earthquake registers 8.0 or higher on the Richter scale.
Because the scale is logarithmic, there is a tenfold increase in the amplitude of the 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.
“We can predict earthquakes, in