The ground shakes daily in central Oklahoma, where natural gas and oil drilling companies inject wastewater into deep wells.
"It's a common occurrence," said Perry, Okla., City Manager Mary Rupp. "It's stressing us emotionally, not really knowing when they will hit and where they are coming from."
The number of 3.0-magnitude or greater earthquakes around Oklahoma City has increased tenfold over the past three years since the drilling began, prompting the U.S. Geological Survey to issue a report arguing that the injection process is inducing the temblors.
It's something Arkansas geologists have said since 2011, when similar earthquakes rattled windows and nerves around Guy and Greenbrier in Faulkner County, where drilling companies used two injection wells. Thousands of quakes -- mostly small ones, but some of 3.0-magnitude or stronger -- rumbled along fault lines beneath the rocky land there.
The U.S. Geological Survey has identified 17 areas in eight states with "frequently induced earthquakes." The areas include Guy and Greenbrier in Arkansas, along with locations in Colorado, New Mexico, Texas, Oklahoma, Kansas, Alabama and Ohio.
Mark Peterson, the director of the survey's National Seismic Hazard Project who is one of the authors of the report, called the increase in the induced seismicity "troubling."
"Earthquake activity has sharply increased since 2009 in the central and eastern United States," he wrote in the report. "The increase has been linked to industrial operations that dispose of wastewater by injecting it into deep wells."
The process involves sending saltwater and wastewater that result from natural gas and oil drilling through a concrete-encased tube thousands of feet into the ground. The Chesapeake Operating Inc. well east of Guy injected fluids at an average of 1,000 pounds per square inch at a depth of between 6,044 feet and 6,212 feet. The Larita Operating LLC well northeast of Greenbrier shot fluids at an average of 2,000 pounds per square inch to depths between 7,800 feet and 10,600 feet.
After thousands of quakes shook the areas, the Arkansas Oil and Gas Commission issued a moratorium in March 2011 on the injection process in a large area of central and north-central Arkansas. It also prohibited new businesses from using injection wells within a 1,150-square-mile area mostly north of Conway.
Officials with several natural gas drilling companies in Arkansas, Texas, Mississippi and Missouri that have operations in northern Arkansas were not available or did not return telephone calls Friday seeking comment about how the moratorium is affecting them.
Since the moratorium was put in place, the quakes have all but ceased in that area, said Arkansas Geological Survey geohazards supervisor Scott Ausbrooks.
"The stress is there," Ausbrooks said, referring to several fault systems that run beneath Faulkner County. "But the activity [of injections] speeds up the clock. If you turn the injections off and turn the faults off, the probability goes down for natural quakes."
There are three major earthquake fault lines that cross Faulkner County. Each runs from northeast to southwest -- the same direction that the New Madrid Seismic Zone runs, Ausbrooks said. Because of the pressure that the Atlantic Ocean exerts on the eastern edge of the United States, faults that run in that direction are more apt to slip and produce larger earthquakes.
The faults in Oklahoma that are generating the bigger quakes also run the same direction.
"These are faults favorable to reasonable stress," he said. "The stress builds up until there's a weak spot in the middle of the plate. The angle of the fault, the age of the fault and the large quantity of stress all came together near Guy and Greenbrier."
Ausbrooks led the study that resulted in the Arkansas Oil and Gas Commission's moratorium. His study showed a marked decrease in the number of quakes once the commission placed a temporary halt on injection wells in March 2011.
In a three-week period leading up to the moratorium, there were 85 quakes of 2.5 magnitude or stronger. In the three weeks immediately after the moratorium, there were only 20.
"We suspected the injection wells were causing the seismicity," Ausbrooks said. "We had high confidence, but we were cautious. We confirmed it when the seismicity went down after the injections stopped.
"We were really the first state that saw that."
For the first time, the U.S. Geological Survey is including induced seismicity in its hazard maps, used for devising building codes, insurance rate structures and risk assessments. The maps, which are released every six years, display probability levels for earthquakes across the continental United States.
In the past, the maps showed blank squares around areas of suspected man-made earthquakes.
In Oklahoma, where officials said the rapid increase in quakes was the catalyst for the U.S. Geological Survey's report, residents saw one or two 3.0-magnitude earthquakes before the injection wells began operating.
In 2013, the area saw 109 earthquakes of 3.0-magnitude or stronger. Last year, it had 585. This year, geologists with the Oklahoma Geological Survey expect to surpass 585 larger quakes by the end of July.
The earthquakes have damaged homes in Perry, Okla., Rupp said. Cracks now spiderweb concrete foundations of homes, downtown buildings showcase bricks lost during the shaking, and the city's library had to replace ceiling tiles and light fixtures that fell during quakes.
The temblors have even fractured city waterlines, Rupp said.
"It's become commonplace," she said. "At first it was pretty scary. No one knew why they were coming. But they definitely are noticeable. Sometimes you hear them coming. Other times it's just a sudden big boom."
But Perry residents are growing accustomed to the shaking.
"It's becoming a social thing," Rupp said. "Now, whenever we feel a big one, someone posts it on Facebook, and everyone else comments about it."
It was the same in Faulkner County when the shaking began, officials said.
"We weren't getting answers at first," said Sue Wrightam, an administrator for the city of Greenbrier. "No one knew why, and that was scary.
"We have a sense now of what was going on, and as it became more common, we were getting used to it."
The Oklahoma Department of Energy and Environment has monitored the quakes there and said it may modify the depths of the injection wells in the area.
Rupp said she doesn't anticipate any moratoriums on injection wells near Perry, however.
"It's a balancing act," she said. "Oklahoma is a strong producer of natural energy. We are a gas and oil state. A lot of people's livelihoods depend on that.
"On the [other] hand, it puts emotional stress on people knowing [that] earthquakes will happen, and it damages property."
Guy Mayor Sam Higdon said he never feared a large earthquake in his town.
"They were never strong enough to scare us, but it made you wonder if it was going to get any worse," he said.
"The people in Oklahoma are going through the same things as we were. They think it's the drilling, and I think they are right. When they quit forcing stuff into the ground, it settled down."
Ausbrooks and the Arkansas Geological Survey aren't resting on their laurels. After determining a relationship between injection wells and earthquakes four years before the U.S. Geological Survey did, Ausbrooks is now focusing on the quakes still popping up farther north of Guy and Greenbrier.
"What are these outliers?" he asked of the temblors near Quitman in Cleburne County and Damascus in Van Buren County. "Are we seeing them because we have more monitors in that area? Are they natural? Are they caused by injections? Is it the [Greers Ferry] lake?
"These are questions we will be researching for the next year."
State Desk on 05/04/2015