U.S. project takes Earth's pulse

When earthquakes devastated Haiti and Chile earlier this year, Nebraskans and Iowans may not have felt the world shake.

But the earth did move — as far away from those epicenters as Aurora, Neb.

In a water well there, a bobber attached to a pen and paper recorded spikes in groundwater levels at the time of the quakes, showing that the same tremors that devastated countries thousands of miles away also made their way to Nebraska.

Over the next few years, using more sophisticated equipment, scientists will learn more about how seismic waves travel and about how the earth moves far below our feet.

The endeavor is part of EarthScope, a national project funded primarily by the National Science Foundation. As part of the project, seismometers have been placed 6 feet deep into the Nebraska soil. Twenty-two seismometers will be placed in Iowa this summer.

“In a simple sense, the hope is to learn more about how the Earth works and, of course, what the crust structure is like,” said Jim Walters, a University of Northern Iowa professor who helped find sites for the devices.

The seismometers are among hundreds being placed across the U.S. Since 2004, they've been placed from west to east, state by state on a grid-like pattern, about 70 kilometers, or 43.5 miles, apart. Most of the machines, which measure the movement of the Earth's surface, are left in place for about two years before being pulled out and leapfrogged to another state farther east.

Those two years are important, said professor Anne Trehu, director of the EarthScope national office, which is based at Oregon State University in Corvallis, Ore. The time allows researchers to collect data from seismic waves received from around the globe. It provides something like a “combination CAT scan/ultrasound of the interior of the Earth,” said Trehu.

Long before scientists are able to look at that data, they need to decide where to put the seismometers. Walters spent last summer working with two students to find the best places in this region. They needed to be evenly spaced and away from interference, said Walters.

Most of the spots chosen are in rural areas, miles away from train tracks or roads with heavy truck traffic, which could cause vibrations.

The data collected from the seismometers in Nebraska and Iowa are available in real time to anyone with an Internet connection at www.usarray.org/researchers/data. Trehu said scientists are free to use the data, which are archived in Seattle.

The work is being done to increase understanding of the Earth and how distant events ripple through its surface, not to evaluate earthquakes specifically in places such as Iowa or Nebraska, said Ray Anderson, senior research geologist for the Iowa Department of Natural Resources.

While earthquakes do hit this region — a 2009 earthquake had its epicenter in Auburn, Neb., and a 2004 quake originated near Shenandoah, Iowa — they are unlikely to be severe, because the region does not rest at a juncture of the Earth's continental plates, Anderson said.

That doesn't mean a severe quake can't happen. In the early 1800s, several major earthquakes damaged the region, originating near New Madrid, Mo. Those quakes caused major damage, but there was low loss of life due to region's sparse population back then. According to historical accounts, the ground was shaken strongly enough to make church bells ring in Boston, said Anderson.

The new seismometers could help scientists better understand how seismic waves travel vast distances. Soon, we'll have a better understanding of the history of the continent, said Trehu.

“Nothing of this scale has ever been attempted in the United States, or, for that matter, the world,” said Walters. “This could provide some of the pieces of the puzzle.”

Contact the writer:

444-1310, elizabeth.ahlin@owh.com

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