In November of 2011, a magnitude 5.7 earthquake ripped through the small Oklahoma town of Prague, damaging more than a dozen homes and toppling a turret on a St. Gregory's University building in nearby Shawnee.
It was the worst of three large quakes to strike the area over several days, and it still as ranks as the worst Oklahoma has ever experienced.
Since then, hundreds more have rattled the state, racking up millions of dollars in damages and unleashing a political and financial maelstrom.
Until 2008, Oklahoma typically had one or two earthquakes of magnitude 3.0 or greater per year, according to the U.S. Geological Survey; since the start of 2015, the state has averaged 2 of this strength or greater per day.
"We have a good record going all the way back to the 1970s of magnitude 3 or larger earthquakes. They increased throughout the central U.S. in 2009, but primarily in just a few states like southern Colorado, Arkansas, Texas and Oklahoma," says Bill Leith, senior science adviser for Earthquake and Geologic Hazards at USGS. "Oklahoma is the most striking case, where the number of earthquakes is now at record levels."
And a growing body of scientific research increasingly connects this upsurge in seismic activity with the recent boom in oil and gas production.
In Oklahoma, oil production has more than doubled in the past five years, climbing from roughly 140,000 barrels per day in late 2009 to just over 360,000 barrels per day in January of this year, according to the U.S. Energy Information Administration.
From 2008 through April 8 of this year, there were 1,063 earthquakes of magnitude 3.0 tallied in Oklahoma by the USGS. This year, through April 8, there were 210, compared with 91 over the same period in 2014. (The smallest quakes that humans can typically feel measure from 2.5 to 3.0.)
The USGS sees a connection: specifically, a link to underground disposal of wastewater generated by oil and gas production.
Oklahoma, Kansas, Texas, Arkansas, Colorado and Ohio have all seen upticks in seismic activity in recent years. (North Dakota and Montana, which contain the Bakken formation, have been largely quake free.) Scientists have been studying the phenomenon in each state.
"In states and in oil fields where there is a lot of production, this water is re-injected, and it's been done for years and years," said Leith. "But that changes the fluid balance in the geologic formation, and that's what has potential of triggering earthquakes."
The phenomenon of man-made earthquakes triggered by changes in water pressure deep in the earth's crust has been studied by geologists for decades. The USGS first documented it in the 1960s, after the U.S. Army injected hundreds of millions of gallons of toxic fluids into a deep disposal well at Colorado's Rocky Mountain Arsenal, resulting in hundreds of quakes.
Since then, examples of "induced seismicity" or man-made earthquakes, have been linked to things from the making of reservoirs and dams to a geothermal project in California. But the connection between quakes and energy production is, to its current extent, relatively new, and the subject of nearly two dozen peer-reviewed papers over the past several years.
To be clear, the USGS does not specifically blame the practice of hydraulic fracturing, known as fracking. "The actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes," stated USGS scientists in a January 2014 report.
"While hydraulic fracturing works by making thousands of extremely small 'microearthquakes,' they are, with just a few exceptions, too small to be felt; none have been large enough to cause structural damage."
Rather, the issue centers around the "injection of wastewater in deep disposal wells," and even then, it does not appear to be the majority of wells that are to blame.
Oil and gas extraction generates water—a lot of it. For every barrel of crude pulled from the ground in Oklahoma, 10 barrels of briny, toxic water accompany it. Some is the water mixture used to blast through rock in the fracking process; but producers say most of it is water that's been sitting deep in the earth for millennia, the remainder of extinct oceans from eons past.
That liquid is the biggest problem since it's exceedingly difficult and expensive to recycle for future use; disposal well injection is the most economical means of dealing with it.
In Oklahoma, ballooning production has resulted in billions of barrels of water that have been injected into more than 4,000 wells in the popular Arbuckle formation. State officials say roughly 3,200 disposal wells are currently active.
However, most wells aren't likely spurring the quakes. Rather it's likely a handful of wells that have been drilled too deep into the bedrock where water is activating faults that may never have been mapped.
Many skeptics, particularly those working in the energy sector, note that Oklahoma has experienced seismic activity to some degree for ages; that this longtime-energycentric state has pulled oil and gas from the ground for decades without ever incurring this recent level of ground-shaking. Even many residents of Prague agree with the industry point of view.
"There is a lot of research which is good in general, but it doesn't give the specificity to be useful," said Kim Hatfield, regulatory and environmental chair for the Oklahoma Independent Petroleum Association (OIPA), the state's industry trade group.
One problem, he said, is a lack of data identifying exact wells that could be triggering quakes.
"The idea of being able to identify the responsible party—that's an issue, and we need to get that right," said Hatfield, who is also president of privately held Crawley Petroleum. "We don't want to paint everybody with the same tar brush."
A recent report from Energy in Depth, an outreach campaign launched by the Independent Petroleum Association of America (with which OIPA is affiliated), asserts that only a tiny fraction of injection wells are to blame. The report focuses on the 14,000 injection wells in North Texas' Barnett Shale formation, arguing that only 0.1 percent "have been identified as a possible cause of earthquakes."
In states where seismic activity has ballooned, resource-strapped regulators and scientists are scrambling to address it. In March, Kansas regulators lowered the maximum injection rates in areas experiencing increased seismic activity. Arkansas and Ohio officials have deemed certain areas off limits to injection wells. In Texas, the state's Railroad Commission, which regulates the oil and gas industry, tightened rules in October.
In Oklahoma, the regulatory process is evolving, in part because the research is.
"The agreement is pretty broad within the seismologist community that going a little bit below the Arbuckle, which we could call the basement, is a very bad idea and carries with it an increased potential for new seismicity," said Matt Skinner, a spokesman for the Oklahoma Corporation Commission, the regulatory body overseeing oil and gas production, including wastewater disposal.
Oil and gas is an economic lifeline in the Sooner State. With companies including Continental Resources, Sandridge Energy and Chesapeake Energy headquartered here, energy's a top industry and widely cited as the top provider of jobs.
It's also home to Cushing, the so-called Pipeline Crossroads of World, where more than $3 billion worth of crude is sitting in above-ground storage tanks. In October several earthquakes struck the area, including a magnitude 4.3. A nearby well that had been drilled into bedrock was temporarily shut down by the state. Energy companies operating pipelines and tank farms in the area say they are keeping an eye on the state's seismic activity, but that they have taken steps to deal with a bevy of risks including earthquakes.