WASHINGTON (AP) – Scientists have determined that a 5.6 magnitude quake in the southwestern state of Oklahoma in 2011 was caused when oil drilling waste was injected deep underground.
That makes it the most powerful quake to be blamed on injections of wastewater, although Oklahoma’s state seismologists say the quake was natural.
The Nov. 6 earthquake near Prague, Oklahoma, in the center of the state, injured two people 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.