Earthquakes rocking the Plains at higher rate, but no evidence ‘big one’ is imminent
07/04/2014 9:19 AM
08/06/2014 12:12 PM
While dozens of earthquakes have been rippling through Kansas recently, most have been barely felt by residents.
But does heightened seismic activity warn of bigger quakes to come?
Not likely, geophysicists and seismologists say. At the same time, they’re quick to add they can’t predict earthquakes.
“Earthquakes don’t follow the rules,” said Don Blakeman, a geophysicist for the U.S. Geological Survey’s earthquake center in Golden, Colo.
That also speaks to the difficulty of identifying why there has been such an increase, which happens to be the main target of officials and scientists.
What the Kansas Geological Survey does know is 56 earthquakes have been recorded in the state over the past seven months, with the vast majority occurring in south-central Kansas.
It’s hard to get an exact handle on how that compares to previous years because the number of earthquake monitors operating in Kansas has changed.
When federal funding was available during the late 1970s and ’80s, the state had 14 monitors that recorded fewer than 20 earthquakes some years and spiked to 45 another, said Rex Buchanan, interim director of the Kansas Geological Survey.
That federal money went away, leaving the state with only two permanent monitors, operated by the USGS near Manhattan and Cedar Bluff.
But even with the current monitoring system – including getting input from Oklahoma’s 30 monitors – officials saw the spike. That jump came after only two earthquakes were recorded in the state from the start of 2013 to mid-August.
“This is one of those things where the more you look, the more you find,” Buchanan said. “Now, having said that, there’s no question we’re having more.”
Rumbling in Oklahoma
Thirty-five of the 56 quakes had a magnitude of 2.5 or less, and five ranged between 3 to 3.5. The largest during the seven-month period was a 4.3 on Dec. 16, occurring just east of Anthony.
All of those numbers pale in comparison to what has come out of Oklahoma. Just over a seven-day period ending Friday, that state’s geological survey has recorded 173 earthquakes.
The state has always had high seismic activity, but nothing like recently.
Oklahoma had more than 2,000 quakes in 2013 and already has surpassed that number in the first three months of this year, said Austin Holland, a seismologist for Oklahoma Geological Survey. More than 100 of those have had a magnitude of 3 or greater, he added.
Oklahoma averaged about 50 quakes per year until 2009, jumping to 1,047 in 2010, Holland said.
A state-record 5.7 earthquake was recorded in November 2011 near Prague, east of Oklahoma City. Some minor injuries and structure damage were reported.
Kansans are well aware of Oklahoma’s quakes because they feel some of them, such as the 3.8 magnitude that happened Saturday morning about 45 miles north of Oklahoma City. That one was felt in Wichita, as well as last Sunday morning’s 4.3 with an epicenter southeast of Enid, Okla.
Kansas’ record quake happened on April 24, 1867, when a tremor with an estimated 5.5 magnitude rocked an area near Manhattan, according to the KGS.
Chimneys toppled and foundations cracked. Two-foot waves were seen in the Kansas River.
Big quake in Kansas?
Seismologist Don Steeples, a professor at the University of Kansas, said the state has the potential for a 6.0 to 6.5 quake.
That’s based on the length of the active fault lines in the state, he said. The longer the line, the greater potential for more energy to drive the quake.
Kansas has segments of the Humboldt Fault Zone that are 40 to 50 miles long, Steeples said. In California, the San Andreas Fault extends more than 600 miles.
The Humboldt runs from near Omaha to Oklahoma City and passes near Wamego and El Dorado.
How much damage a quake does at a certain magnitude depends on a number of factors, including soil type and how well buildings and houses are constructed.
“In this country, it usually takes a quake with a magnitude of at least 5.0 before someone gets hurt or there is much significant damage,” Blakeman said.“But a 5.0 in China may kill a lot of people, especially in the rural area where the construction isn’t that good.”
There was enough concern about Tuttle Creek Reservoir withstanding an earthquake that the U.S. Corps of Army Engineers spent $175 million for an upgrade project that was completed in 2009.
As to whether smaller earthquakes quakes foretell the coming of a bigger one, Steeples said it’s possible – if the quakes are naturally occurring.
“There’s a general rule of thumb that’s true in most places in the world that for every 10 natural earthquakes with a magnitude of 3, you’ll have a 4,” he said. “For every 10 with a magnitude of 5, you’ll have a 6 and so on up to whatever the maximum is for the area, which is determined by the fault length.”
Even then, Steeples said the progression to a higher magnitude could take 200 years.
But if the quakes are induced by human activities, he said, “I’d be less concerned about something substantially bigger.”
Blakeman, the USGS geophysicist from Colorado, said, “The general wisdom is if you have a fault somewhere and it’s experiencing relatively small quakes, scientists have felt, well, that should be relieving some of the stress and should decrease the chance of a big one.”
But Blakeman noted that’s not what happened in Chile, where a series of small quakes preceded last Tuesday night’s deadly 8.2 that struck the South American country.
“It’s not possible to predict an earthquake – regardless of what some people say out there,” he said.
Eyes on fracking
Scientists and officials are in the process of trying to determine if activities by the oil and gas industry are inducing seismic activity.
When oil or gas is pulled from underground, a large amount of salt water comes with it. That water is separated and injected into the ground in disposal wells.
A process called hydraulic fracturing – commonly known as fracking – uses a mixture of water, sand and chemicals under high pressure to release oil and gas from rock.
Steeples, however, said not enough disposal wells are drilled in an area to create enough pressure to cause an earthquake of 5.0 or so.
Holland, the seismologist from Oklahoma, said man-made activities in the oil and gas industry don’t add enough energy to cause the earthquakes.
“We’re releasing the natural energy that’s stored within the earth,” he said. “We’re maybe changing the timing of these earthquakes, but we’re not creating them.”
In general, “the jury is still out” on whether those activities are causing earthquakes, Buchanan said.
USGS seismologist Justin Rubinstein said, “Nobody wants to make a declarative statement until there’s really a smoking gun.”
Rubinstein, who is based in Menlo Park, Calif., is the deputy chief of a project that is looking at whether the quake increase is caused by human efforts.
He’s leading the study in Kansas and recently had five quake monitors placed temporarily in Sumner and Harper counties to help in the research.
“We’ve seen seismic activity creeping up in the Mississippian limestone play,” Rubinstein said. “We wanted to get out in front of that, but we didn’t quite do that.”
Kansas quake panel
Kansas Gov. Sam Brownback appointed a committee in February to study whether the oil and gas activity is behind the surge in earthquakes.
Buchanan is on that panel, which has met several times to get input from experts. On April 16, the committee will hold an invitation-only meeting in Wichita. Stakeholders from the oil and gas industry, scientists and environmentalists have been invited to attend.
A public comment period will follow for 30 days before the committee makes its recommendations to Brownback by early summer.
The process figures to be complex and controversial.
“Unfortunately, earth science is very messy,” Rubinstein said.
While fracking has been around for decades, that’s not much history in terms of geological time to get a firm handle on its effect, scientists say.
“If those earthquakes are related to fracking,” Blakeman said, “then we’ll have an idea what to do about it. Or whether we want to do anything about it. That’s something we have to figure out.
“But as far as having a big one from all this, I would say it’s a fairly remote possibility.”
Just the same, Holland said, people should be aware these earthquakes are happening at an increasing rate.
“I don’t want to sound alarmist by any stretch of the imagination,” he said. “There’s no need to panic. But people should have a general awareness of earthquake hazards.”