OKLAHOMA CITY (AP) — The 37 wastewater disposal wells to be shut down in north-central Oklahoma, where a 5.6 magnitude earthquake struck this weekend, are just a fraction of the state's total number.
There are about 4,200 total wells across the state and about 700 in a 15,000-square-mile "Area of Interest" created by the commission to address earthquakes in the area that includes the epicenter of Saturday's temblor near Pawnee.
The earthquake tied a November 2011 quake as the strongest in recorded state history and was felt as far away as Nebraska, but no major damage was reported.
Not all of the state's wells operate simultaneously, Oklahoma Corporation Commission spokesman Matt Skinner said.
"We estimate that at any one time, there are about 3,200 active disposal wells," Skinner said.
An increase in magnitude 3.0 or greater earthquakes in Oklahoma has been linked to underground disposal of wastewater from oil and natural gas production, and since 2013, the commission has asked wastewater-well owners to reduce disposal volumes in parts of the state where the temblors have been most frequent.
The "area of interest" includes another 211 adjacent square miles that's under the jurisdiction of the Environmental Protection Agency, and Skinner said the commission doesn't know how many wells may be involved there.
Gov. Mary Fallin declared a state of emergency in Pawnee County because of the earthquake. State and local emergency management officials and officials from the U.S. Geological Survey assessed damage Sunday, according to Pawnee County Emergency Management Director Mark Randell.
"We're just trying to determine just how widespread" the damage is, Randell said. He described it as minor to moderate, with some collapsed chimneys and fallen sandstone facing off buildings; no buildings collapsed.
None of the utilities, pipelines or fuel infrastructure in the area had major damage, either, the commission said. The Oklahoma Department of Transportation inspected 180 state bridges within a 30-mile radius of the epicenter and reported minor cosmetic damage to two structures, but all are open and safe for travel.
ODOT said the inspections across six counties took about six hours to complete.
"We are pleased with the speed and efficiency of our crews in their response to this event and dedication to ensuring public safety," ODOT executive director Mike Patterson said.
The U.S. Army Corps of Engineers is inspecting all dams within a 50-mile radius of the epicenter, including the Birch, Cleveland Levee, Heyburn, Kaw, Keystone, and Skiatook dams.
Key energy-producing areas in both Oklahoma and Kansas saw an uptick in quakes in the first half of this decade, but took different approaches. Kansas moved quickly to limit volume in wastewater disposal wells, while Oklahoma concentrated on the depth of the disposal. Kansas saw a 60 percent drop while the frequency of quakes in Oklahoma continued to climb.