The sudden uptick in earthquakes in Oklahoma has plenty of folks in the area asking whether the onset of tremors is linked to hydraulic fracking. But for transportation officials, the more immediate question is: Can our bridges withstand the seismic activity?
The state has 6,800 bridges -- 468 of them classified as "structurally deficient" -- and most were not built with frequent earthquakes in mind. But earthquakes in Oklahoma have become so common that inspectors are being called to check out bridges several times a week, often on weekends or in the middle of the night. Officials from the Oklahoma Department of Transportation (ODOT) recently paid for their counterparts in California, the only state with more earthquakes than Oklahoma in the contiguous United States, to visit and share their expertise.
ODOT is using the visit to develop an interim policy, says Paul Green, ODOT's director of operations. To that end, they are looking into implementing several checklists that California currently uses in assessing bridges after earthquakes.
California Department of Transportation (Caltrans) officials also discussed which bridge designs were most susceptible to damage, says Tim Tegeler, ODOT's director of engineering. Inspectors especially keep an eye out for bridges that are narrow, have unstable bearings or that have supports that are not perpendicular to the ground. Caltrans showed off a unique computer program it uses called QuakeCast that alerts inspectors minutes after an earthquake to which bridges are most likely to be damaged. Oklahoma is unlikely to adopt a similar program at this time, but it helps to know which bridges to carefully monitor.
Paul Green, ODOT's director of operations, says that even though the state has made strides in fixing up worn-out bridges, it will have nearly 1,200 spans that are more than 80 years old by 2021. "Those bridges were designed in the Model A era," he says. "They certainly weren't designed for today's traffic loads. So anything that puts additional stress on those bridges is worrisome."
Oklahomans have long lived with nature's destructive forces, as they regularly face tornadoes, droughts and ferocious winter storms. And Oklahoma sits on a seismically active region. But the increase in the number, scope and location of earthquakes in the state in recent years has been dramatic. Just five years ago, residents could expect to feel one to three earthquakes a year. Since 2009, though, the state has had an average of 40 a year.
The Oklahoma Geological Survey recently said there is not enough evidence to link the increase in earthquakes to the rapid expansion of hydraulic fracturing in drilling for oil and gas. The group noted that some of the techniques used in fracking had already been used in Oklahoma for years previously without causing earthquakes.
The U.S. Geological Survey, on the other hand, concluded that the jump in the number of earthquakes does "not seem to be due to typical, random fluctuations in natural seismicity rates." It is studying whether fracking caused a recent "swarm" of earthquakes, which included the largest in Oklahoma history, a 5.6-magnitude temblor that originated about 50 miles east of Oklahoma City. Similarly, Kansas is looking to see if there is a link. And geologists in Ohio recently reported that fracking is likely the cause of an uptick in earthquakes there.
For centuries, Oklahoma has experienced more earthquakes than most of the country, notes Paolo Gardoni, the director of the MAE Center at the University of Illinois at Urbana-Champaign, which studies how to minimize damage from natural and man-made disasters. Whether Oklahoma's earthquakes were caused by fracking or not, however, the public is paying attention to the dangers they pose. It is an opportunity, Gardoni says, for Oklahoma officials to evaluate whether they need to strengthen their bridge design code or fix structures.
Gardoni notes that much of California's earthquake mitigation only came after the 1994 Northridge earthquake, even though Californians knew they lived in an earthquake zone. "Until something happens, until there is some damage, until maybe somebody dies, too many things don't get done," Gardoni says. "Now, after a few earthquakes occurred [in Oklahoma], it may be the time to reassess and think a little bit ahead of time."