Eight earthquakes strike heart of U.S. shale oil and natural gas industry
The largest of the tremors recorded by the USGS was a magnitude-4.2 event shortly before 3 a.m. local time in the town of Edmond, which is designated in a state area of interest.
The Oklahoma Corporation Commission has ordered oil and gas operators to cut back on disposal well operations and closed some wells in response to increased seismic activity in those areas.
There's been no new well activity in the area in terms of drilling or hydraulic fracturing as of July, state regulators said after a recent outbreak
A statement from regulators, published by local KWTV News 9, said investigators were on the ground near the cluster of tremors in the Edmond area.
"The investigation is focused on oil and gas wastewater disposal wells that inject into the Arbuckle formation, the state's deepest formation," the statement read.
"The earthquakes have been clustered close together in an area where there is a known fault. There are no Arbuckle disposal wells at or very close to the location."
Tremors are not associated with hydraulic fracturing in and of itself.
Oklahoma seismicity peaked in 2015, with more than 900 tremors of greater than magnitude-3 recorded.
In January 2016, Governor Mary Fallin approved $1.4 million in funding to expand efforts to address the issue.
Last week, Oklahoma experienced 623 tremors of greater than magnitude-3.
Three of the eight events recorded Thursday by the USGS were less than magnitude-3. ■