An unusual and widely felt 5.6-magnitude quake in Oklahoma in 2011 was probably caused when oil drilling waste was pushed deep underground, a team of university and federal scientists concluded.

That would make it the most powerful quake to be blamed on deep injections of wastewater, according to a study published Tuesday by the journal Geology. The waste was from traditional drilling, not from the hydraulic fracturing technique, or fracking.

Not everyone agrees, though, with the scientists’ conclusion: Oklahoma’s state seismologists say the quake was natural.

Continue reading →