Oklahoma Gov. Mary Fallin declared a state of emergency after a magnitude 5.6 earthquake struck nine miles northwest of Pawnee this morning.

The record-tying earthquake in north central Oklahoma also prompted regulators to order the shutdown of 35 disposal wells used by frackers over a 500-square-mile area.

Today’s quake tied the state’s previous record in 2011. It shook parts of the Midwest and was felt from Houston to North Dakota. Six after-shocks followed the quake, including one that registered 3.6.

Earlier this week, a 3.2 quake occurred in the same spot as today’s, which is about 70 miles northeast of Oklahoma City

Scientists believe hydraulic fracking operations are responsible for the growing number of Oklahoma earthquakes. The injections can alter stresses that hold geologic faults together and let them slip, unleashing earthquakes.

An increase in earthquakes measuring 3.0 or higher in Oklahoma has paralleled the growing volume of underground wastewater disposal from oil and natural gas production. According to earthquaketrack.com, there were 15 earthquakes today in the state, 114 in the past month, and 2,506 in the past year.

In parts of the state, the number of tremblers matches those in northern California. In 2014, Oklahoma surpassed California as the nation’s most quake-prone state.

Oklahoma’s quakes are shallow — five miles or less below the surface — while California’s go as deep as 400 miles. Deep surface earthquakes are stronger and more destructive.

Sean Weide in Omaha, Nebraska, told The Associated Press that he’d never been in an earthquake before and thought he was getting dizzy. Weide said he and one of his daughters “heard the building start creaking” and said it “was surreal.”

At least one minor injury was reported today. A man protecting his child suffered a head injury when part of a fireplace fell on him. The man was treated at a hospital and released.

Buildings in Pawnee’s “downtown” area were cracked and the sandstone facing on some buildings fell, according to reports.

Oklahomans have a complicated relationship with the fracking industry. An estimated one in six workers in the state owe their paychecks either directly or indirectly to the industry. But fears about the growing frequency and magnitude of the seismic events have alarmed large numbers of residents.

Oil industry and government officials deny that hydraulic fracking is causing the quakes. Oilmen have pressured scientists and geologists at local universities not to address the subject.

The wells ordered shut down today will remain closed for 10 days.