A Prediction Gone Awry

One day last fall a call came to the UW news office from a distraught assistant at the Bellevue School District. She had heard that the UW predicted an earthquake will hit the Seattle area that week. If this is true, the district wants to be ready.

This isn't Southern California, she is told. There earthquakes occur so frequently -- and the geological evidence is so abundant -- that scientists can issue 50-50 odds for major tremors on a scale of years.

The most precise estimate for the Northwest can be found in a recent issue of Washington Geology. Anyone spending half of his or her life in Western Washington "should expect to live through a major earthquake." No doubt, many people spent their entire lives in Western Washington between 1872 and 1949, ignorant to earthquake risks. Those dates bracket the state's strongest historical earthquakes.

When asked about the rumor, Steve Malone, a UW seismologist and research professor of geophysics, replies, "We're being inundated with calls on that. I don't know why or where these things get started."

They don't get started at the UW Seismology Laboratory, wired to more than a hundred seismographs in Washington and Oregon. The lab monitors thousands of earthquakes a year. But only a few dozen are strong enough to be felt (Richter magnitude 3 or greater). Fewer are strong enough -- magnitude 5 or greater -- to cause damage.

From the data the UW collects, no technique exists that would allow anyone to predict whether an earthquake is more likely to occur today than 50 years from now.

But earthquakes themselves can be useful predictors -- of volcanic eruptions, a specialty of Malone's. If volcanic earthquakes come in furious succession -- "swarms" Malone calls them -- and continue for three days while growing in intensity, an eruption is likely. Swarms preceded the 1980 eruption of Mount St. Helens.

"Seismic monitoring is a quantitative way of saying something about the vigor of a mountain," Malone says. "As a seismologist that's what I go by. If nothing goes bump in the night, nothing is going to happen." --Bill Cannon

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