PRAGUE, Okla. (AP) - Scientists say an earthquake "swarm" continues to affect central Oklahoma nearly two years after a record 5.6-magnitude quake rattled the state.
A new report by the U.S. and Oklahoma geological surveys says more than 200 magnitude 3.0 or greater earthquakes have hit Oklahoma's midsection since January 2009.
The study released Tuesday says that one to three magnitude 3.0 earthquakes or larger occurred yearly in Oklahoma from 1975 to 2008, but the average grew to around 40 earthquakes per year from 2009 to 2013.
State and federal scientists continue to investigate why the earthquake rate has changed so dramatically throughout central Oklahoma, and are exploring possible links to waste water disposal related to oil and gas production in the region.
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