Big Quakes Trigger Smaller Quakes

Reported December 2008

SALT LAKE CITY, Utah (Ivanhoe Broadcast News) -- An earthquake in Alaska could trigger one near you, even if you're not in an earthquake-prone area, new research shows. Seismologists are now finding earthquakes in some unexpected places.

City Hall in Park City, Utah, is undergoing a $10 million seismic update. Park City is near the Wasatch Fault, an area overdue for an earthquake, so leaders have been concerned about earthquake-proofing the building for years.

"It's something we absolutely expect," Ron Ivie, a building official in Park City, told Ivanhoe. "The question is, 'What day?'"

While earthquakes along fault lines are expected, seismologist Kris Pankow and her research team recently found slow-moving seismic surface waves, or L waves, from large earthquakes travel along the ground and trigger smaller earthquakes as they go.

"It's sort of like if a tree falls in the forest, does anyone hear it?" Pankow, assistant director of the University of Utah seismic stations in Salt Lake City, told Ivanhoe. "The same question was here: If the seismic waves go by everywhere, do they generate earthquakes everywhere?"

Unlike the earthquake risk in Park City, Pankow says the risk of these smaller earthquakes is minimal. The team tracked 15 large earthquakes and found 12 of them actually triggered smaller jolts. These are different than aftershocks because they happen miles away and sometimes hours or days later.

The team also found earthquakes in unlikely places like Canada, Australia and western Africa.

Pankow doesn't want to alarm anyone. She says the triggered earthquakes that have been observed have been small. Without a seismograph, you may not even notice them.

Seismologists still don't completely understand why earthquakes happen. Pankow and her team hope their work with these dynamically triggered earthquakes will help lead to an answer.

The American Geophysical Union and the Incorporated Research Institutions for Seismology contributed to the information contained in the TV portion of this report.

Click here to Go Inside This Science or contact:

Kristine Pankow
Salt Lake City, Utah 84112-0011
(801) 585-6484
pankow@seis.utah.edu

Peter Weiss
American Geophysical Union
Washington, DC 20009-1277
(800) 966-2481
http://www.agu.org
pweiss@agu.org

John Taber
Education and Outreach Program Manager
Incorporated Research Institutions for Seismology
Washington, DC 20005
(202) 682-2220
taber@iris.edu

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