Magnitude 4.1 quake hits north Oklahoma, second in 2 days

By Jon Herskovitz (Reuters) - A magnitude 4.1 quake hit near the north Oklahoma town of Medford on Friday, the second temblor in two days to hit the area where energy extraction takes place. The U.S. Geological Survey said the quake, initially reported as a magnitude 4.6, struck at 4:40 p.m. at a shallow depth of 4.9 miles (8 km) with the epicenter 9 miles (15 km), north-northwest of Medford. There were no immediate reports of major damage or injuries. A magnitude 4.7 earthquake struck northern Oklahoma early on Thursday, rattling residents out of their beds and shaking the ground across a 100-mile (160-km) radius that included the city of Tulsa and the state of Kansas. The state's oil and gas regulator, the Oklahoma Corporation Commission (OCC), moved within hours on Thursday to implement additional curbs on the use of saltwater disposal wells that scientists have linked to a sharp rise in seismic activity in the state. Saltwater, a normal byproduct of oil and gas extraction work that boomed after 2009 following improvements in hydraulic fracturing and horizontal drilling, is injected into deep disposal wells and underground caverns. The quakes come about a month after an earthquake with a magnitude of 4.5 struck near the U.S. crude oil hub of Cushing, Oklahoma. That quake occurred just days after regulators imposed new rules to limit the use of saltwater disposal wells in a bid to prevent temblors in the area. It also implemented additional measures after that quake. (Reporting by Jon Herskovitz in Austin; Editing by Sandra Maler)

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