Scientists are working to determine what caused six earthquakes near Stroud Friday morning. The cluster started with a 4.2 magnitude earthquake, and five more quickly followed nearby.
While many of Oklahoma’s earthquakes have been linked to wastewater disposal into the earth's crust, researchers still have yet to discover how long it takes the faults to react to water pressure, so this cluster could point to additional events in the future.
Now, a feverish accumulation of data is underway at the Oklahoma Corporation Commission and Oklahoma Geological Survey to map and analyze a nearly straight line of earthquakes from northwest to southeast.
“We have no mapped faults around that event,” notes OCC spokesman Matt Skinner.
OGS seismologists say the cluster reveals a previously unknown vertical fault halfway between Stroud and Cushing. The first quake rumbled about five miles under the earth's surface, with the subsequent quakes growing weaker and shallower along the line.
OCC's induced seismology team can look at this event in relation to nearby injection sites using the Oklahoma Well and Seismic Monitor, or OWSM tool, as an inspector gathers information in person.
Skinner says, “He has gone through the area looking for anything we should have been notified about and weren’t, but there’s nothing there.”
There are eight small wastewater injection wells currently in use in a ten mile radius of the earthquakes, and the OCC can graph how many barrels each of them is pumping daily. The team is exploring the possibility that these injections either pushed the pressure on the fault to its tipping point, or the earthquakes are a delayed response to vastly greater amounts of wastewater injected by large wells shut down after the Cushing event last year.
“Researchers have long warned us there is no instant off-switch,” says Skinner, “and if you are successful, it will be a gradual success. Well, we’re seeing a gradual decline in the earthquake rate.”
OCC's team expects to meet with OGS seismologists to compare notes on Monday.