Regulators were again assessing their response to recent seismic activity on Monday after the second 4.7 magnitude earthquake in less than two weeks shook northwestern Oklahoma.
The latest, west-southwest of Medford in Grant County, occurred at 3:49 a.m. Monday. Eight earthquakes of magnitude 4.2 or greater have occurred in that area this year.
All told, Oklahoma has had more than 600 earthquakes of 3.0 magnitude or greater in 2015, easily a record. The two 4.7 quakes are the strongest in four years.
Geologists attribute the increased seismicity to the high-pressure injection of wastewater from crude-oil production into certain rock formations.
The state, through the Oklahoma Corporation Commission, has responded by ordering some 635 disposal wells to modify or cease intake volume. Only three weeks ago, on Nov. 9, the commission ordered the operators of nine wells near Medford to modify their operations.
Last week a researcher with the U.S. Geological Survey said the strategy seemed to be working, at least in the vicinity of Cushing, 40 miles west of Tulsa.
Recent wall-rattlers in Grant, Alfalfa and Major counties might provide arguments against that, but Oklahoma Geological Survey Director Jeremy Boak said in a phone message Monday that part of the state had been relatively quiet until the two recent outbreaks.
The area, Boak said, "had had a substantial decline from a larger and longer pulse of earthquakes in early 2015 and a smaller one in July and August."
The Corporation Commission's attention has been focused primarily on a 12-county area in northern and central Oklahoma where a disproportionate share of the activity has been concentrated.
"My bottom line is that it's a fairly large area and the Corporation Commission has been working sequentially to address the larger earthquakes," Boak said.
"The earthquakes themselves are coming in pulses. The Corporation Commission is doing the best it can to sort this all out and is doing a reasonable job. "It's a tricky thing to get your hands on."
For Tulsans, the earthquakes to this point have been more or less an annoying novelty.
In other parts of the state, however, they are damaging buildings and jangling nerves.
"The problem is we're being totally reactionary as opposed to proactive," state Rep. Cory Williams, D-Stillwater, told The Associated Press. "We wait for a seismic event, and then we react to it, which is an abysmal policy for handling something that can cause catastrophic damage to property and/or life."
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