A solid case could be made that Oklahoma did something in its past to anger the cosmic gods. Its history is riddled with tales of man-made fortune seemingly lost to the whims of Mother Nature. Known for the spirit-crushing drought that led to the Depression- era Dust Bowl, Oklahoma also lies—depending on the map—in the heart of Tornado Alley. Having lived in the state for several years in the early 2000s, I can say with authority that the bitter winter winds from the north can slice through the heaviest of jackets. Earthquakes were not something we worried about back then, though, so imagine my surprise when towns like Pawnee, Perry (where I once lived) and Prague made the news for their Richter—and not Beaufort—scale readings.
Prior to 2009, the state might have experienced one to two low-magnitude earthquakes per year, according to a U.S. Energy Information Administration report on earthquake trends in the state. In the years since there’s been a dramatic increase in the number of earthquakes. This well-publicized increase brought with it intense scrutiny and analysis on the cause of these seismic events since they often occur in areas where oil and gas production from shales has increased. Studies have shown that many of the earthquakes are linked to the injection of produced water into a deep sedimentary rock formation known as the Arbuckle Group.
“The Group sits on top of the [pre-Cambrian] basement and provides the conductive pathway by which pressure is transmitted to faults at depth,” said Jeremy Boak, director of the Oklahoma Geological Survey.
Boak, speaking at the Unconventional Resources Technology Conference held in late July, noted there were 903 earthquakes of at least a 3.0 magnitude in 2015 in the state. That number fell to 623 in 2016. As for 2017, he estimates the number of earthquakes will drop farther, sharing that “we’re on track to maybe be as high as 300 this year.”
The U.S. Geological Survey reports this decline may be related to decreased wastewater injection, a result of production declines since the 2014 drop in oil prices. This, combined with stricter injection practices, could account for the drop earthquake frequency, Boak noted.
The earthquakes are strongly related to the development of the Hunton Limestone in southern Oklahoma and the Mississippi Limestone to the north, he said. Unlike the Mississippi Lime (where Pawnee and Perry are located) that has experienced the “lion’s share of seismicity,” the Hunton gets far less attention because relatively fewer earthquakes have occurred in that area, he said. “On the other hand, the Prague earthquake happened there, and our most recent magnitude four earthquake happened within that area.”
Even at 300, lower magnitude earthquakes for the year is still too high, but it is good to see efforts are leaving the state a little less shaken than before. And as history has shown time and again, Oklahomans will endure for the better.