Earthquake rattles the heartland; some speculate it was human-caused

A preliminary 5.6 magnitude earthquake struck on Saturday morning near Pawnee, Oklahoma, according to the U.S. Geological Survey.

A preliminary 5.6 magnitude earthquake struck on Saturday morning near Pawnee, Oklahoma, according to the U.S. Geological Survey.

PAWNEE, Okla. — A 5.6 magnitude earthquake struck Saturday morning near Pawnee, Oklahoma, and rattled through at least six surrounding states in the US heartland, according to the US Geological Survey.

The earthquake was also felt in Kansas, Arkansas, Missouri, Texas, Nebraska, and Iowa, according to the USGS.

The Oklahoma Corporation Commission, a regulatory agency that examines the state’s fuel, oil, gas, public utilities and transportation industries, is “reviewing disposal wells in the vicinity of the earthquake near Pawnee,” Oklahoma Gov. Mary Fallin said via Twitter.

The Oklahoma Department of Transportation is checking bridges for damage and structural engineers are assessing building safety according to Fallin.

The earthquake damaged at least one historic building in Pawnee, Oklahoma, city officials told CNN.

“It’s an old historical building about 100 years old. It’s still standing but some of the outer layers of sandstone fell, it could be cosmetic damage, we don’t know yet,” said Pawnee Mayor Brad Sewell.

“A quake this size would shake for about 15 seconds and it was a shallow quake, about 7 kilometers (4.35 miles) deep,” said Randy Baldwin, a USGS geophysicist.

There is no clear evidence of major damage from the earthquake, Pawnee Chamber of Commerce manager Tom Briggs told CNN.

“We had some buildings, some of the older structures, delaminate. The fire department and electricians and police are going through the area,” Briggs said.

No injuries have been reported.

There have been a total of 11 earthquakes in the same area Saturday, the USGS said. The largest was at 7:02 a.m. (8:02 a.m. ET), with the preliminary 5.6 magnitude. The other quake magnitudes ranged from 2.7 to 3.6.

Despite minimal damage, the quake did set off anxious speculation on social media.

A recent report released by the USGS showed that people in parts of Texas and Oklahoma now face similar ground-shaking risks from human-induced activity, such as fluid injection or extraction, as residents face from natural earthquakes in California.

The agency outlined the risk of these so-called “induced” earthquakes, noting that Oklahoma City and the surrounding region face a 5 to 12% chance of damage from an earthquake in 2016.

The Oklahoma Corporation Commission “is working to get firmer data” to pinpoint the epicenter of the quake, said commission spokesman Matt Skinner.

Skinner said earthquakes in Oklahoma are generally not caused by fracking, but rather by pressure from the disposal wells.

“The disposal wells dispose into the state’s deepest formation, the Arbuckle formation, which is right above what we call the basement. The basement is above where the critical faults lie that shift and make earthquakes,” he explained.

“There’s all kinds of theories as to why it puts pressure on the basement faults, but somehow that is happening and we have taken many actions based on that,” Skinner said.

With earthquakes in the central and eastern United States, “the ground is softer, so the seismic waves have a much farther travel distance then an earthquake in California or Nevada,” said Robert Sanders, USGS geophysicist.