In recent years, Oklahoma has featured more earthquakes than anywhere else in the United States -- even more than California. So far in 2014, the Sooner State has served as host to some 240 small earthquakes, each with a magnitude of at least three.
Since 2008, more than 2,500 earthquakes have shook the grounds surrounding Jones, Okla., a small town smack dab in the middle of the state.
Most of the quakes are too small to pose any great risk to human health or property, but residents and environmentalists are still concerned.
"We wanted to figure out what the root cause was, what was actually causing the entire part of central Oklahoma to light up," said Katie Keranen, who experienced the Oklahoma quakes firsthand in 2011 and is now a geophysics professor at Cornell University.
Now Keranen and her colleagues have linked the swarms of quakes in middle America to the some 4,400 underground disposal wells, where wastewater -- the byproduct of the booming oil and gas industry's nonstop drilling -- deep into the ground.
The water used to break up and extract oil and gas from shale rock inevitably mixes with the valuable fuel commodity, forcing excavators to separate the oil and gas from the water back at surface level. Once removed, however, operators are left with a whole bunch of salty water laden with toxic chemicals.
"As part of the business model, you have to be able to dispose of these very large volumes of saline water," explained Bill Ellsworth, from the U.S. Geological Survey. "You can't treat it; you can't put it into the rivers. So, you have to inject it underground."
And it's this process that's apparently causing all the quakes.
"Once we had the earthquake locations and the fluid pressure increases in space and time, we were able to correlate those two together and figure out how much fluid pressure went up at each earthquake location from those wells," explained Keranen. "And what we were able to find is that the fluid pressure at the earthquakes went up enough to trigger the earthquakes in basically each case."
In addition to tweaking regulations to ensure these wells don't further aggravate fault lines, Keranen says oil and gas companies can do a better job of monitoring the pressure in their wells.
A number of states throughout the midwest are considering how to more closely supervise the growing oil and gas industry and mitigate potential negative consequences -- like earthquakes.