The Emporia Gazette

May 28, 2012

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A series of earthquakes over the weekend in Oklahoma that could be felt as far north as Kansas City has area residents wondering — could we see a Big One here in the Great Plains?

The weekend’s earthquakes began at 2:12 a.m. Saturday with a magnitude 4.7 quake in Lincoln County in central Oklahoma, about 50 miles east of Oklahoma City. No major damages or injuries were reported in that quake, but its tremors could be felt in Wichita. Oklahomans felt aftershocks throughout the day Saturday.

The seismic activity jumped into high gear Saturday night with a magnitude 5.6 earthquake occurring just before 11 p.m. According to Don Blakeman, a geologist with the U.S. Geological Survey, Saturday night’s earthquake was the largest ever recorded in Oklahoma. The previous record-holder was a magnitude 5.5 quake that occurred in El Reno, Okla., in 1952.

“That doesn’t mean, back before there were instruments to record it, that there weren’t quakes this large there,” Blakeman said.

According to reports from the Associated Press, damage from the quake was minimal, but it did tumble a chimney in Sparks, Okla., and buckle a highway there.

And over the weekend the activity continued, as aftershocks were felt throughout Sunday.

“It can be expected with these very large, shallow quakes that there’s a pretty active aftershock series that’s going on now,” Blakeman said. “We can expect it to continue for a while.”

The effects of the temblor could be felt here in town and had some Emporians on edge Saturday night.

“It seemed like it lasted about a minute,” said Gerald Goll of Emporia. “The walls were shaking, and for a little bit I started to feel like I should get off the second floor. Then it just stopped.”

“I lived seven years in California and five in Seattle and where do I feel my first earthquake? Emporia, Kansas,” said Emporian Dan Ferrell.

Some described the tremors as being close to the railroad tracks when a train passed, and still others were asleep or didn’t notice the effects of the quake.

According to Blakeman, the magnitude 4.7 quake was simply a precursor to the larger quake Saturday night.

“It’s kind of a semantic thing,” he said. “By definition, the largest earthquake in a series is called the mainshock. So what we’re doing now is calling the 4.7 a foreshock.”

Seismic activity has been increasing in Oklahoma over the past two years, Blakeman said, and geologists are looking into exactly why that is. Data from the Oklahoma Geological Survey shows that there were 1,047 earthquakes in the state in 2010.

As Blakeman explained, the earth’s crust is broken up into 10 or 12 major plates, with a great many minor plates as well. The plates are driven around by the release of heat from the earth’s core, and earthquakes are expected on the boundaries of the larger plates, locations like California, Japan and Alaska. But even though Oklahoma is relatively centered on a plate, it contains many faults. And though earthquakes aren’t exactly expected in the area, they’re really no surprise, either.

“Even though Oklahoma, being part of the mid-continent, is centered on a plate, not on a boundary, there are still stresses within those crustal plates for moving around,” Blakeman said. “We think they have interior stresses as well, and so we occasionally get these kinds of quakes, and we think it’s just part of that stress release.”

Saturday’s earthquake activity occurred near the Wilzetta fault, also known as the Seminole uplift, according to the Oklahoma Geological Survey. A magnitude 4.0 aftershock occurred Sunday morning just after 9 a.m.

As to the question, Could it happen here? According to the Kansas Geological Survey, earthquakes are rare in Kansas, but they aren’t unknown. More than 25 temblors struck the state between 1867 and 1976, and more than 100 were recorded from 1977 to 1989. The most destructive earthquake in Kansas occurred in 1867 along the Nemaha Ridge, near the Humboldt fault zone; the Nemaha Ridge runs from the northeast to the south-central part of the state. The 1867 quake caused damage in Manhattan and was felt as far away as Iowa.

While a major quake in this part of the country is unlikely, contingency plans are in place for the area, according to Rick Frevert, director of the Lyon County Office of Emergency Management.

“When we did our hazard analysis it was one of the lower hazards out there, but it was on the radar screen,” Frevert said. Over the summer, emergency management teams conducted an exercise specifically geared toward an earthquake in Kansas, but the timing of the exercise was unfortunate. “It was during the time frame of the Reading and Joplin tornadoes, so it didn’t get a lot of publicity, and several of the players that were going to participate dropped out because they had real disasters to take care of,” he said. “But there are contingency plans in place, just like with other disasters.”

One major concern for this area as far as natural disasters go is the Wolf Creek Nuclear Operating Corporation in Coffey County. According to Jenny Hageman, media relations director for Wolf Creek, steps were taken to ensure the safety of the plant over the weekend. The plant has seismic monitors to record natural events and procedures are in place to ensure the safety of the plant during a natural disaster.

Saturday night’s quake was not enough to set off the plant’s seismic alarms, but per Wolf Creek’s emergency procedures control operators inspected components of the plant based on reports of the quake from on-site security personnel.

“They were able to verify that there was no damage,” Hageman said. “Our seismic monitors did not register enough movement to trigger an alarm, so once we performed all the inspections we were able to exit the emergency procedures.”

Plant operators are highly trained and continue their training about one week out of every six, Hageman said. Part of that training includes time on a simulator control room in which operators practice emergency scenarios.

Even though earthquakes in this part of the country are rare, geologists say there is always the possibility of seismic activity.

“One thing I think a lot of people don’t understand is that there are faults everywhere,” Blakeman said. “Lots and lots of faults. Most of them are completely inactive, or at least we think they are.”