Doug Stanglin

USATODAY

Oklahoma regulators on Saturday shut down 37 wastewater wells connected to oil and gas production after a magnitude-5.6 earthquake — matching the strongest quake ever to hit the state — jolted north-central Oklahoma.

Some parts of Oklahoma now match Northern California for the nation’s most shake-prone, and one Oklahoma region has a one-in-eight chance of a damaging quake in 2016, with other parts closer to one in 20.

The quake, centered in rural Pawnee County, could be felt over a seven-state area, the U.S. Geological Survey reported.

Gov. Mary Fallin said on Twitter that the shutdown was a "mandatory directive" covering 725 square miles in Osage County, just northwest of the quake's epicenter. She said the Oklahoma Corporation Commission, which ordered the shutdown, was in touch with the Environmental Protection Agency regarding the emergency measures.

Fallin said three homes in Pawnee County were damaged and that at least three buildings in the city of Pawnee sustained some level of damage. An inspection of state highway and turnpike bridges also had turned up "very minor issues," she said.

Pawnee County Emergency Management Director Mark Randell said one homeowner was treated and released from the hospital after suffering a minor head injury when part of a fireplace fell on him as he protected a child, the Associated Press reported. Randell said building damage in Pawnee was mostly brick and mortar from buildings dating to the early 1900s.

Pawnee Mayor Brad Sewell told KOKI-TV that some sandstones from damaged historic buildings tumbled onto the sidewalk during the quake. Parts of central Pawnee, a town of about 2,000 people, were cordoned off until the buildings could be examined.

The Pawnee Nation, which has its tribal headquarters in the area, declared a state of emergency and said damage to its buildings was so extensive they were being closed pending further inspection.

An increase in magnitude-3.0 or stronger earthquakes in Oklahoma has been linked to underground disposal of wastewater from oil and natural gas production. According to an analysis published by the Tulsa World in January, the volume of wastewater disposed climbed 81% over six years, coinciding with the state’s increase in earthquakes.

Since 2013, the OCC has asked wastewater-well owners to reduce disposal volumes in parts of the state.

“All of our actions have been based on the link that researchers have drawn between the Arbuckle disposal well operations and earthquakes in Oklahoma,” OCC spokesman Matt Skinner said Saturday of the latest directive. “We’re trying to do this as quickly as possible, but we have to follow the recommendations of the seismologists, who tell us everything going off at once can cause an (earthquake).”

Saturday's jolt rattled a wide area of the Great Plains, including Missouri, Kansas, Texas, Arkansas, Nebraska and Iowa.

The magnitude-5.6 quake equals a temblor that struck the town of Prague, in Lincoln County, in November 2011, according to the USGS.

While hundreds of quakes shake Oklahoma annually, they have rarely been felt in northeastern Oklahoma, the Tulsa World notes.