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An earthquake struck northern Oklahoma early Saturday morning, rattling houses and waking residents in the region around Pawnee, about 74 miles north of Oklahoma City. Preliminary measurements show the quake had a magnitude of 5.6 — believed to be one of the strongest in state history.

The quake was felt in five states, according to the U.S. Geological Survey: Oklahoma, Kansas, Missouri, Arkansas and Texas. It struck just after 7 a.m. local time, at a depth of 6 kilometers (3.7 miles).

Joe Wertz / StateImpact Oklahoma

Oklahoma is still experiencing an unusually large amount of shaking, but the rate of earthquakes recorded in 2016 is down from last year.

The slowdown is likely due to reductions in the amount of waste-fluid the oil industry is pumping into disposal wells, which are thought to be causing most of the shaking.

A spike of earthquake activity near the city of Blanchard has prompted state regulators to investigate oil and gas operations in the area.

At least nine quakes have been recorded near the small community southwest of the Oklahoma City metro, including 3.4 and 3.1-magnitude temblors within days of each other.

The shaking has ranged from light to moderate. The Blanchard quakes are outside a 15,000 square-mile zone established earlier this year, where regulators asked oil companies to reduce activity at disposal wells thought to be triggering the shaking.

“The number of earthquakes in Oklahoma has fallen 25% in 2016 compared with a year earlier,” the Wall Street Journal’s Erin Ailworth reports.

Joe Wertz / StateImpact Oklahoma

Oklahoma’s insurance commissioner has formally declared the state’s market for earthquake insurance is “uncompetitive.” The regulator says Oklahomans are unfairly limited when shopping for quake insurance.

119 companies sell earthquake insurance in Oklahoma, but Commissioner John Doak says just four companies have controlled more than half the market in recent years.

The commissioner says the industry has moved to raise rates and limit coverage as the shaking — linked to oil and gas activity — surged.

Oklahoma oil and gas companies are asking a federal judge to dismiss a lawsuit filed by members of an environmental group that seeks to reduce production waste that could be fueling a spike in earthquakes.

Oklahoma Insurance Commissioner John Doak is considering regulations that create a “file-and-use” system for earthquake insurance policies, “meaning insurers would have to submit rate increases to the Oklahoma Insurance Department in advance,” The Oklahoman’s Brianna Bailey reports.

Insurance companies moved to limit their exposure as Oklahoma’s earthquake rate exploded, according to an investigation by Reuters.

Examining thousands of pages of documents from the Oklahoma Insurance Commission, reporter Luc Cohen found the efforts by nearly a dozen insurance companies “often occurred at the expense of homeowners”:

Watch the 60 Minutes report on the high incidence of earthquakes in Oklahoma.