Quakes at the Lakes: They could happen, but don't duck just yet

Sue Evers, the Earthquake Program Manager for FEMA Region VII, recalls a December tremor that triggered fault reports up and down the Iowa-Nebraska border.

Ray Anderson, the Senior Research Geologist for the Iowa Geological and Water Survey, mentions a Feb. 10 earthquake felt in Chicago.

And neither one of them is ready to dive under a desk over fear of a tectonic shaker in northwest Iowa.

Not that it couldn't happen -- Evers says a 5.0 earthquake can happen almost anywhere in the United States.

Her territory, FEMA Region VII, is comprised of Iowa, Kansas, Missouri and Nebraska. It's also home to several faults, most notably the New Madrid and the Humboldt-Nemaha. In March of 1964, a 5.1 magnitude earthquake near Merriman, Neb., cracked roads, collapsed banks of the Niobrara River, and shook dishes and canned goods from shelves. A FEMA statement said a similar-sized earthquake in 2008 hit Mount Carmel, Ill., causing damage to some buildings including a high school gymnasium, and was felt in 23 states including all Region VII states.

In December 2009, six different earthquakes -- three of which were greater than 3.0 magnitude -- rattled windows and shook the ground in various regions across Oklahoma, Arkansas, Nebraska and Missouri.

"At a magnitude 4 or 4.5 you start seeing some effects like pictures moving on the wall or falling off the wall, trees swaying," Evers said. "At a 5, you might get some cracks if you were in the impact zone."

While that may sound scary, the northwest part of Iowa just isn't positioned to take a direct hit from cranky collision of continental plates, according to the experts.

"In northwest Iowa you have a lower expectation or a lower risk for a damaging earthquake occurring there, compared to other places," Evers said. "Risk from damage would probably come from a large earthquake outside of Iowa."

Iowa doesn't have volcanos, Anderson explained: "You're generally looking at a fault zone, or a fracture in the rock. Then you're looking at some sort of a differential stress across it. The stress on one side is a little higher than the other, and it's going to cause the rocks to slip along that fault. We have lots of faults in Iowa, but none of them have been active -- at least what we could call active -- for quite a while."

The result is 13 historic earthquakes in Iowa -- "if you can believe them all," Anderson said, referring to data complied by a St. Louis University professor. He and his students went back through old records and produced the most comprehensive list of past quakes in the state. The U.S. Geological Survey used the findings before compiling a list of its own.

Evers sees the Wabash Valley fault (near the Illinois-Indiana border) or the New Madrid seismic zone (south of St. Louis) as potential culprits.

"Both of those zones are capable of producing really giant earthquakes," Anderson agreed. "The largest in U.S. history -- in the continental U.S. history -- have been down there in New Madrid. It's certainly capable of doing that again sometime."

The largest series of earthquakes in the continental U.S. occurred in southeast Missouri in 1811 and 1812.

It released so much energy in southern Missouri that it shook church steeples enough to make the church bells ring in Boston, Anderson said.

The energy doesn't come out in a circular field, however. Because of the grain of the continent, shock waves are typically directed in a northeast, southwest direction.

"Even one of those giant earthquakes -- you would feel it up in your area -- it would wake people up for sure, but it wouldn't cause any damage up there," Anderson said.

So what about the rumble felt in northern Illinois a few weeks ago? Glaciers are a possibility -- Anderson said the ground is rebounding, very slowly, in response to all of the glacial ice that was on the region a million years ago. The weight of all this ice pushed the continent down a little bit. When the ice melted away, it (the continent) is slowly coming back up.

"We don't understand the geology of the earth very well and there's lots of little things that can pop up," Anderson said. "That earthquake in the Chicago area is a perfect example. We don't know of any faults up there. There's no reason there should be an earthquake going on up there."

"But there was one," he said. "Things happen."

WHAT TO DO:

Midwesterners expect and prepare for a variety of seasonal hazards such as extreme snow, ice, flooding, tornadoes and severe weather. But the non-seasonal threat of earthquakes may not register on every family's hazard scale, according to the Federal Emergency Management Agency.

If an earthquake occurs, get under heavy furniture and do not run outside, according to Sue Evers, the Earthquake Program Manager for FEMA Region VII.

"When you feel the earth shake, drop, cover and hold on," she said. "After the shaking stops, check yourself for injury, look around, check your family members and look up. Most injuries occur from things falling. When you go to the door, open it carefully, look out, look up and move away from anything that might fall -- especially power lines, structures and trees."

Anchoring heavy objects to solid walls, such as tall book cases, file cabinets, computer servers and heavy pieces of furniture also is recommended