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Stonework litters the sidewalk outside an empty jewelry store at the corner of Sixth and Harrison in Pawnee, Oklahoma, U.S. September 3, 2016 after a 5.6 earthquake struck near the north-central Oklahoma town. REUTERS/Lenzy Krehbiel-Burton

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By Lenzy Krehbiel-Burton

TULSA, Okla. (Reuters) - One of the strongest earthquakes ever recorded in Oklahoma rattled a state where seismic activity linked to energy production has become a growing concern and sent tremors through six neighbouring states, a federal agency said on Saturday.

The quake, which struck 14 km (9 miles) northwest of Pawnee in north-central Oklahoma at 7:02 a.m. CDT (1302 GMT), had a magnitude of 5.6, matching in strength a temblor that hit the state in 2011, the United States Geological Survey reported on its website.

There were no immediate reports of injuries in Pawnee, where about 25 percent of the residents are Native Americans. Damage in the town appeared to be minor.

"You heard it before it happened," Pawnee resident Jasha Lyons Echo-Hawk said. "Watching my drawers all shake out and my headboard rattle, it felt like I was watching ‘Paranormal Activity.’ It felt like I was in a movie."

The earthquake, which had a depth of 6.6 km (4.1 miles), could fuel concerns about the environmental impact of oil and gas drilling, which has been blamed for a spike in minor to moderate quakes in the region. Oklahoma's economy is heavily dependent on energy production, which accounts for one of every four jobs in the state.

Pawnee Mayor Brad Sewell said the tremor lasted nearly a minute, far longer than previous ones that lasted only a second or two. Part of the façade of an early 20th-century bank building had fallen into a downtown street, he said.

“We have had a spate of quakes over the last several years, but nothing like this,” he said. “It was a long, sustained quake.”

The likelihood of casualties and damage from the earthquake, was low, the USGS said. Most homes in north-central Oklahoma were resistant to earthquakes, it said on its website.

Oklahoma geologists have documented links between increased seismic activity in the state and the injection into the ground of wastewater from oil and gas production, according to a report from a state agency last year.

Oklahoma is recording 2-1/2 earthquakes daily of a magnitude 3 or greater, a seismicity rate 600 times greater than before 2008, the Oklahoma Geological Survey (OGS) said.

The spike has put Oklahoma at the centre of a national debate over whether wastewater from oil and gas production triggers earthquakes. The process separate water extracted with gas and oil, and then re-injected into deep wells.

The drilling technique known as hydraulic fracturing, or "fracking," also generates large amounts of wastewater, but the OGS report said fracking is responsible for only a small percentage of the total volume of injected wastewater.

Zachary Reeves, a seismologist with the USGS National Earthquake Information Center in Golden, Colorado, said the agency had received reports of the Oklahoma quake from South Dakota, Wisconsin, Kansas, Missouri, Arkansas and Texas.

(Additional reporting by Ian Simpson in Washington and Chris Prentice in New York; Writing by Frank McGurty; Editing by James Dalgleish)

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