SEATTLE- Just before a massive landslide came down wiping out a half mile of Highway 410 in Yakima County, residents said they could hear cracking, and moaning from the ground.
It turns out that seismometers that are part of the Pacific Northwest Seismic Network run out of the University of Washington heard them too. But what the earthquake-detecting seismometers picked up was the geological correlation with what people heard.
That gave scientists at the University of Washington an idea. If the sounds were an accurate predictor of a large slide, could potential slide areas that present a public hazard be wired up in advance? And when the instruments picked up that earth movement, even movement that people couldn't hear, could roads be blocked and people evacuated in advance?
Wes Thelen is the U.W. Seismologist who led a team back over to the slide about two weeks after it happened and put out a network of more than a dozen small seismometers and several large ones to listen. They picked up the sounds of movement.
Today in a laboratory at the University's Seismology Lab, he demonstrated the tracings, the seismographs that show the vibrations picked up by the instruments, most of which had to be downloaded into computers once they were recovered.
They are not earthquakes. But seismometers pick up all sorts of noises - from blasting at mines, to heavy trucks rumbling over logging roads to rock slides. But the big slide along SR 410, which also destroyed or rendered uninhabitable eight homes provided an opportunity that rarely comes along, especially on this kind of scale.
"What it showed you is the precursory signals as they're coming in," says Thelen. "We're really in the infancy in terms of studying this stuff. We don't have many examples of seeing these slides in real time."
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