By Heidi Koontz

Distant wastewater disposal wells likely induced the third largest earthquake in recent Oklahoma record, the February 13, 2016, magnitude 5.1 event roughly 32 kilometers (nearly 20 miles) northwest of Fairview, Oklahoma, according to a new study. These findings from the U.S. Geological Survey were published in Geophysical Research Letters, a journal of the American Geophysical Union.

At the time, the Fairview earthquake was the largest event in the central and eastern United States since a 2011 magnitude 5.7 struck Prague, Oklahoma. The 5.1 magnitude event occurred southwest of a group of high-rate wastewater disposal wells greater than 12 kilometers (7.45 miles) away. In the region surrounding the Fairview earthquake sequence, the volume of fluid injected increased seven-fold over three years.

”The fact that seismicity is rather limited near the high-rate wells while the Fairview sequence occurred at a relatively larger distance from these wells, shows us the critical role preexisting, though possibly unknown, fault structures play in inducing large events,” said William Yeck, a USGS scientist and lead author of the study. “The rapid deployment of seismic stations by the USGS allowed us to precisely locate the aftershock sequence. High-quality data sets such as these are critical when trying to understand the shaking produced by these events and therefore are an important basis for earthquake hazard modeling.”

Earthquakes in this area primarily occur at depths of six to nine kilometers (3.7 – 4.9 miles), roughly 3.5 to 6.5 kilometers (2 – 4 miles) below the Arbuckle Group in which wastewater is typically injected.

On September 3, 2016, Oklahoma experienced the largest earthquake since 2011 when a magnitude 5.8 earthquake occurred near Pawnee, Oklahoma.

While the relationship between the Pawnee earthquake and wastewater injection is still under investigation, studies such as this further scientific understanding of the complex relationship between wastewater disposal and earthquakes.

– Heidi Koontz is a public affairs specialist at USGS. This post originally appeared on the USGS website.