A magnitude-5.8 earthquake and a series of smaller aftershocks in Oklahoma has led to the discovery of a new fault line.
The discovery stoked fears among some scientists about other unknown faults that could be triggered by oil and gas wastewater that’s being injected deep underground.
State and federal regulators this week said 32 disposal wells in northeastern Oklahoma must shut down because they are too near the newly discovered fault line that produced the state’s strongest earthquake on record on Sept. 3.
The quake shook Wichita and many other parts of Kansas. It caused minor damage to some city and county buildings.
Jeremy Boak, head of the Oklahoma Geological Survey, said it’s possible that a large “pulse” of disposed wastewater is slowly moving deep underground and triggered the temblor along the new fault located near the town of Pawnee, farther east than most of the previous earthquake activity in Oklahoma.
“My inclination is to worry about the (fault) we don’t know about yet, more so than about another very large earthquake in this area,” Boak said.
“My general feeling is that the rate of earthquakes is declining. I’m more concerned, I think, about whether there’s another one of these faults out here that is queued up and ready to go.”
Boak said it’s also possible that some aftershocks greater than magnitude 4 could still be triggered along the newly discovered fault that has yet to be named.
The Pawnee quake damaged more than a dozen buildings and slightly injured one man when part of a chimney collapsed. It shook several states, including Kansas, Missouri and Arkansas, and was reportedly felt more than 1,000 miles away in Florida and Nevada, according to the U.S. Geological Survey.
Five more earthquakes occurred in the southern Great Plains on Tuesday: four in Oklahoma and one in Kansas, the survey’s online records show. The Kansas earthquake occurred at 11:18 a.m. 6 miles northwest of Harper in Harper County.
It measured 3.2 and was more than 5.5 miles deep. Tuesday’s activity followed at least four earthquakes that occurred in northern Oklahoma late Monday, including a 2.8 that occurred not far from the epicenter of the 5.8 quake earlier this month.
Scientists, including those at the OGS, think the vast majority of the earthquakes in Oklahoma are triggered by the injection of wastewater from oil and gas production deep into the earth.
After the Pawnee quake, state and federal regulators immediately ordered disposal wells to shut down or reduce volume of wastewater within a 725-square-mile area. That area was expanded on Tuesday to encompass 67 total wells in more than 1,100 square miles.
Some of the disposal wells that were initially ordered to completely shut down will be allowed to resume at lower volume, regulators said.
In all, the 75,000 barrels a day of wastewater that was being injected in the area is being reduced to about 35,000 barrels a day, said Jim Marlatt of the oil and gas division of the Oklahoma Corporation Commission.
Forcing oil and gas operators to stop injecting wastewater or reduce the amount they can inject means they can’t produce as much oil and natural gas, which can cause a serious financial hardship, said Chad Warmington, president of the Oklahoma Oil and Gas Association.
“These are multimillion-dollar wells in some cases that you can’t operate any more, period,” Warmington said. “If you take away your disposal activity, there’s nothing else you can do with that water.”
Still, Warmington said the industry also is concerned about the quakes and is working with regulators to try to stop them.
“As long as we’re making decisions based on good data and good science, we’ll live with it,” Warmington said.