Oklahoma has had more magnitude 3 or higher earthquakes so far this year than in all of 2013, a statistic that’s led some to fear that the uptick in quakes is related to fracking in the state.
In 2013, according to Bloomberg News, Oklahoma experienced 109 earthquakes of magnitude 3 or higher. That number was reached again just a little over three months into 2014. The state experienced its 109th magnitude 3 earthquake of 2014 on April 6, followed by a magnitude 4 earthquake on April 7. In the last 30 days alone, Oklahoma has had 133 earthquakes of magnitude 2.5 or higher — the base level at which seismologists say earthquakes can be felt — and the April 7 quake was the fifth of that magnitude felt by the state since March 30.
Before 2009, Oklahoma experienced few 3.0 or higher earthquakes — no more than three a year from 1991 to 2008. But in 2009, the amount of fracking wastewater injected deep into the ground has risen, and so has the number of earthquakes in the state. Since 2009, earthquake activity in Oklahoma has consistently been about 40 times higher than the average of the previous 30 years.
Some of these earthquakes — particularly the series that hit near Langston, Oklahoma — are occurring close to injection wells, so state officials are working to determine whether the injection of wastewater played a role in causing these earthquakes.
“We certainly likely have cases of earthquakes being caused by different oil and gas activity,” Austin Holland, a research seismologist with the Oklahoma Geological Survey, told Bloomberg. “Evaluating those carefully can take significant amounts of time, especially when we’re swamped.”
Earthquakes have been linked to the fracking process in Oklahoma before. Earlier this year, a study from the U.S. Geological Survey found that wastewater injection was the likely trigger for a swarm of earthquakes in the state in 2011, including a 5.7 magnitude quake that was largest earthquake associated with wastewater injection. That earthquake was likely triggered by an earlier earthquake, which was likely triggered by wastewater injection.
“The observation that a human-induced earthquake can trigger a cascade of earthquakes, including a larger one, has important implications for reducing the seismic risk from wastewater injection,” USGS seismologist Elizabeth Cochran said.
Oklahoma isn’t the only state to experience a rash of earthquakes in recent years. In Ohio, a recent uptick of earthquakes corresponds with increased fracking in the state, according to a Columbus Dispatch investigation. However, officials say the recent earthquakes in Ohio were not related to wastewater injection, and are instead looking into whether fracking itself triggered the earthquakes. A December study from Southern Methodist University did link a string of earthquakes in 2009 and 2010 in Cleburn, Texas to the injection of fracking wastewater into the ground. The area was hit by a group of more than 50 earthquakes in 2009 and 2010, but before 2008, the Fort Worth Basin of Texas had never experienced an earthquake.