Big quake: not if, when

Site on New Madrid, Wabash Valley faults spells trouble for Tri-State

By JACOB BENNETT Courier & Press staff writer (812) 464-7434
October 9, 2005

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Houses will collapse as if made of cards. Bridges will tumble into the gaps they span. Two-thirds of the city of Evansville could be in the dark for a week.

Just as meteorologists predicted a big hurricane would one day swamp New Orleans, geologists here say it is only a matter of time before the Tri-State is rocked by a powerful earthquake.

The Evansville area is nestled between two quake centers: the notorious New Madrid Fault, which in 1811 and 1812 birthed three of the most powerful quakes to ever hit the nation, and the Wabash Valley Seismic Zone, which is known to have produced magnitude 7 quakes, which can do serious damage over large areas.

"It wouldn't be a surprise if we had one tomorrow," said Joan Gomberg, an earthquake seismologist with the U.S. Geological Survey, which is partnering with local groups to map potential hazards in the area. "We know that, at least in the past, there have been significant earthquakes there. It's certainly prudent to take precautions."

The Wabash Valley Seismic Zone could pose the more imminent danger through its numerous faults, which run northeast through Posey County and into Vanderburgh and Gibson counties.

Gomberg said there have been at least two magnitude 7 quake quakes there.

A magnitude 7 quake centered at or near Evansville, on the Wabash Valley Seismic Zone, at 2 p.m., when schools and offices are at capacity, would be the worst-case scenario. Computer models organized by the Central U.S. Earthquake Consortium showed that a 2 p.m. quake could kill 129 people and send 400 more to the hospital. Two-thirds of the area's households could be without power for a week. Fires could scorch half the city's area.

The area's schools, hospitals and emergency response facilities fared well in the model.

The Evansville area most vulnerable stretches east from Downtown between the Ohio River and the Lloyd Expressway. Any Tri-State area by a river or lake is at risk, because shaking pushes water into the sands and clays to cause liquefaction, which turns the soil into an unstable fluid.

Risk of flooding is considered minimal, said Jeff Schaefer, a regional geotechnical specialist with the U.S. Army Corps of Engineers in Louisville, Ky. That's because even if the quake was big enough and close enough to damage the levees, the river would have to be up to major flood levels to pose a threat.

About $750,000 has been spent in Southwestern Indiana in the last few years to retrofit seven fire stations, including two in Evansville, one in Newburgh and one in New Harmony, in hopes the crews and equipment would be unscathed and could focus on rescues. Gas shut-off valves were put in several hospitals, including Gibson General and Worth Regional in Oakland City. Deaconess Hospital now has a seismically safe well separate from the public water system.

The Ohio River twin bridges stretching from Evansville to Henderson, Ky., the U.S. 60 Spottsville Green River Bridge and the Audubon Parkway Green River Bridge were not retrofitted because they were deemed sturdy enough to survive a significant quake. Thousands of smaller bridges, mostly on rural county and state roads, aren't as sturdy. Commercial buildings in Indiana have been regulated for seismic standards since 1989; residential buildings since 2002. Kentucky also has statewide codes with seismic standards; Illinois does not.

Most buildings built in the early 1900s or before would fall down, said Roger Lehman, Evansville-Vanderburgh County's building commissioner.

In the event of a large New Madrid quake, St. Louis, Nashville, Tenn., and Memphis, Tenn., likely would all be hit. Since federal response targets the greatest need for the greatest amount of people, those cities would be in line before Evansville, said Sherman Greer, director of the Evansville-Vanderburgh County Emergency Management Agency.

"We'll probably be on our own for a couple of weeks," Greer said. Another concern is the area's emergency communications system, said state Rep. Dennis Avery, D-Evansville. State officials have installed a uniform system in northern and central Indiana, so that all counties and municipalities will be able to communicate with each other, but the system won't be complete in Southern Indiana until next year.

Vanderburgh County's radios are compatible with the system now, but most of the surrounding counties, including Warrick, Gibson and Posey, will need to purchase new equipment, said Dave Smith, implementation director of the Integrated Public Safety Commission, which is overseeing the $78 million project.


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