Oklahoma rocked by one of its biggest earthquakes in history

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What is believed to be one of the biggest earthquakes in Oklahoma’s history struck the state on Saturday morning, with a preliminary magnitude of 5.6. No major injuries have been reported.

The quake hit just after 7 a.m. local time and was felt across several states, including Nebraska, Iowa, Oklahoma, Kansas, Missouri, Arkansas and Texas, according to the U.S. Geological Survey. The epicenter was about 8 miles northwest of Pawnee, a city of fewer than 3,000 people.

“The eastern U.S. in general has older, more stable rock layers, so (earthquakes) are felt across a wider area,” USGS geophysicist John Bellini told the NewsHour.

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While there were no immediate reports of significant damage on Saturday, the Tulsa Police Department asked that people refrain from going to Pawnee, to leave roads open for emergency workers.

The magnitude ties with the size of the last record-setting quake, which hit south of Pawnee in November of 2011.

Oklahoma has seen an unprecedented surge in the number of quakes in the last five years. Before 2009, the state used to average only a handful of 3-magnitude or above earthquakes a year. But they have significantly increased every year after – reaching a peak of 900 in 2015.

The spike has been connected to a rise in domestic oil production, partly due to technology called hydraulic fracturing, or fracking, which bursts rock formations with water and sand to get to the oil and gas.

After the oil and gas is extracted and separated, the briny wastewater leftover is pumped back into the ground.

As NewsHour Weekend reported in January, some wells produce 20 barrels of salty wastewater for every barrel of oil. And last year, energy companies in Oklahoma injected 1.5 billion barrels of water back into the ground. This reduces friction and releases energy that geophysicists say causes the earth to shake.

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Regulators have been putting caps on wastewater injections, which may have contributed to a decrease in the number of quakes.

Bellini said there was no way to know whether Saturday’s earthquake was directly related to oil production. People on social media, however, started making their own connections.

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