Scientists: Big Oklahoma quake in 2011 was man-made

The Nov. 6, 2011, earthquake that injured two people and damaged 14 homes was caused by injections of wastewater, scientists found.

WASHINGTON — A team of scientists has determined that a 5.6-magnitude quake in Oklahoma in 2011 was caused when oil drilling waste was injected deep underground.

That makes it the most powerful quake to be blamed on deep injections of wastewater, although not everyone agrees. Oklahoma's state seismologists say the quake was natural.

The Nov. 6 earthquake near Prague, Okla., injured two people, damaged 14 houses and was the strongest Midwestern quake in decades.

The new report says there was a smaller quake at the site of an old injection well, and that triggered the larger tremor. Records show the well pressure rising dramatically in 2006. The scientists say both combine to make a strong case that waste injections caused the quake.

The report was released Tuesday by the journal Geology.

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