The Commercial-News, Danville, IL

May 18, 2013

Area at risk for quake damage


DANVILLE — People accept the potential for severe weather, flooding and even the potential for tornadoes in east central Illinois.

But ask a person if they’re ready for the next earthquake to arrive and most people will unabashedly shake their heads.

East central Illinois is in the range of two fault lines for the Midwest.

The New Madrid Seismic Zone lies within the Central Mississippi Valley from Cairo through southeastern Missouri, western Kentucky, western Tennessee and northeast Arkansas. The epicenter of the zone is located just west and northwest of Memphis, Tenn.

Closer in distance, the Wabash Valley Seismic Zone is located in southeastern Illinois and southwestern Indiana, with its epicenter located between Mt. Vernon, and West Franklin, Ind.

The Wabash Valley Seismic Zone experienced an earthquake with a magnitude of 5.2 as recently as April 2008. It was the largest recorded in the state of Illinois at the time and the early morning quake shook residents in Vermilion County.

The New Madrid is the most active seismic zone in North America east of the Rockies. According to the U.S. Geographic Survey, earthquakes in the Midwest and eastern U.S. are felt over a wider range than similar magnitude earthquakes in the California area. The range can multiply almost 10 times.

Vermilion County Emergency Management Agency Director Ted Fisher said earthquakes may not be the first thing on people’s minds, but catch the public’s attention quickly.

“They’re not frequent, but when we do have them, the phone lines light up and everything,” he said.

The most recent quake was measured last month in southern Illinois when a 2.7 magnitude earthquake hit near the town of Benton, south of Mt. Vernon.

While earthquakes are less frequent locally than their severe weather counterparts, the role EMA takes is much more prominent.

Fisher said aside from any potential structure damage, EMA is expected to inspect and account for any possible cracks and damage to roads and bridges as well as pipelines in the county. The recovery from an earthquake could be more costly as a result, because of the need to bring in licensed engineers to look for any potential damage.

Even sinkholes are a concern EMA must check for after a quake.

“A tremor heavy enough could open up some of those,” Fisher said, adding that there are a litany of tunnel mines and shaft mines south of U.S. Route 150 that could lead to a sinkhole.

According to the USGS, officials estimate a 25-40 percent chance of a magnitude 6.0 quake along the New Madrid Fault in the next 50 years. The estimates do not predict where along the five-state zone that the quake could occur.

But while the New Madrid zone is larger that the Wabash Seismic Zone, it’s the smaller area that poses the bigger threat to east central Illinois.

Geophysicist Robert Williams with the U.S. Geological Survey said a 6.0 quake along the New Madrid fault would not lead to destruction in this area.

“You would definitely feel shaking. But you’re unlikely to get any damage,” he said.

“The Wabash (seismic zone) is something more to worry about for damage in Danville,” Williams added.

He pointed out that while the New Madrid is larger, the Wabash zone has had more 5.0 magnitude or larger earthquakes as of late.

Three have been recorded there: 1968, 1987 and 2008.

According to Williams, the power from earthquakes tends to travel farther in the eastern United States and Midwest because of the rock on this side of the Rocky Mountains.

He said the more dense rock on this side allows the power from a tremor to flow further than in California, where the rock is softer and broken up.

Fisher contends Vermilion County has to consider more than just feeling the physical effects of an earthquake in the New Madrid or even Wabash Valley zones. Large quakes in either location would result in an influx of residents to other cities, including potentially Danville.

“People could come up here to get away from the disaster or to seek shelter and hospitals,” he said, saying the effect could be a “services type.”