(Bloomberg) -- One of the strongest earthquakes among manyin Oklahoma since the introduction of hydraulic fracturingstruck early Saturday near a complex of oil-storagefacilities, leading state regulators to order the suspensionof about 37 wastewater-disposal wells.

The Oklahoma CorporationCommission, which regulates the state’s oil industry, iscontacting the operators of the wells in a 500-square-mile areaaround the town of Pawnee, Governor Mary Fallin said in a Twitterpost. Oil storage and pipeline facilities at Cushing, Oklahoma, 25miles (40 kilometers) south of Pawnee, were undamaged, according tothe commission and four of the companies that operate there.

Matched strongest quake ever in state

The 5.6-magnitude quake matched a November 2011tremblor as the strongest ever in the state, the U.S. GeologicalSurvey said, and was followed by at least eight others measuring asmuch as 3.6. The surrounding region of Oklahoma and Kansas, acenter of oil exploration using fracking, has had almost 80 quakesof magnitude-4 or higher over the past decade.

Oklahoma, a region not known for seismic activity, began havingearthquakes in 2009, the same year area oil companies began usingfracking to shatter deep rock layers to extract oil and gas.Fracked wells produce large quantities of wastewater, whichdrilling companies inject into ultra-deep disposal wells. Criticsblame earthquakes on this practice.

Saturday’s tremor hit the area about 7:02 a.m. Oklahoma time,the USGS said. It was also felt in Kansas, Missouri, Texas,Arkansas, Tennessee, Iowa, Illinois and Indiana, according toUSGS’s reporting system for members of the public.

No damage at petroleum facilities

Officials for Enterprise Products Partners LP, Kinder Morgan Inc.,Magellan Midstream Partners LP and Enbridge Inc., which operatepetroleum terminals, pipelines and storage facilities in Cushing,said their sites sustained no damage and that operations werenormal. Last week, the crude storage levels at Cushing stood atnearly 64 million barrels, according to the Energy Information Administration data.

“Following the earthquake, Enbridge employees were directed toconduct visual inspections of tanks, manifolds and otherfacilities,” spokeswoman Jennifer Smith said in an email. “TheCushing terminal is currently operating normally.”

A spokesman for the Oklahoma Corporation Commission, MattSkinner, offered similar comments.

Tremors were also felt at the Cooper Nuclear Station inBrownville, Nebraska, about 350 miles north of Pawnee, butoperations were unaffected and no damage was reported, said DrewNiehaus, a spokesman based at the plant.

Related: Oklahoma Insurance Commissioner issues bulletin toinsurance companies on earthquake exclusions

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