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Ed Yeates reporting Everybody has theorized about it for years, but now there's proof! Large earthquakes do, in fact, trigger other earthquakes, sometimes on the opposite sides of the Earth.
In 1992, a magnitude 7.3 earthquake hit Landers, Calif. Within minutes and hours of that Lander's event, a quake rattled Las Vegas. Then 60 small quakes broke loose near Cedar City. Quakes also hit two volcanic locations on California's Cascade Range. And quakes showed up in old craters in Washington state and Yellowstone Park.
Scientists had believed large quakes cannot trigger other quakes hundreds of miles away, but apparently, they can. In fact, University of Utah seismologist Chris Pankow and her colleagues, who've carefully analyzed two different kinds of surface shock waves from 15 major earthquakes over the past 16 years, say the triggering occurs not only hundreds, but thousands of miles away.
Chris Pankow, a University of Utah seismologist, says, "What we clearly found from the Sumatra earthquake is a triggered event in Ecuador, which is at the antipode - so opposite side of the globe - there was triggering."
The triggered earthquakes are smaller, but they happen globally and sometimes in areas not prone to earthquakes. So, why are some faults triggered by a distant event? One theory, Pankow says, is "You have something really ready to go, and you just put a little energy, and that sort of accelerates the time on the fault to failure."
Another theory says shock waves shake the pores loose in geothermal areas like Yellowstone Park or places with a high water table. In some cases, increased fluid pressure may actually lubricate a fault, so it slips a bit.
Seismologists don't know for sure what's happening on the receiving end, but now that they do know triggering occurs, they'll move to the next step, hoping to understand the mechanics. "It's happening everywhere following large earthquakes, and that is exciting and really interesting to me as a scientist," Pankow said.
Another possibility: could a different kind of earth mechanics, involving what seismologists call static stress, affect our own Wasatch fault? One 25 mile section of the fault breaks loose with a magnitude 7 or greater earthquake, triggering yet another quake on another section of the fault. It could happen!
The University of Utah partnered with the University of Texas and the United States Geological Survey for this landmark research. The full study appears today in Nature Geoscience.
E-mail: eyeates@ksl.com
