Oklahoma City residents woke early New Year's Day to a magnitude 4.2 quake. Earlier this week, a magnitude 4.3 quake struck the same area.

The state isn't historically known for earthquakes, but NPR's Nell Greenfieldboyce told our Newscast unit that Oklahoma "has recently seen a dramatic rise in seismic activity." Here's more:

"If you think of a U.S. state associated with earthquakes, it's probably California. But really, you should think Oklahoma. In 2015, Oklahoma hit an all-time high, with more than 800 quakes of magnitude 3 or greater. That busts the record set in 2014, which topped the previous record set the year before. State officials have said this rise is very unlikely to represent a naturally occurring process. The concern is that these quakes may be linked to oil and gas drilling — specifically, the way wastewater produced by the drilling is pumped into deep underground disposal wells. Oklahoma is trying to address the issue. It has a coordinating council on seismic activity that includes regulators, scientists and industry representatives."

Joe Wertz of StateImpact Oklahoma further explained the connection between the oil and gas industry and the increasing number of quakes, on Weekend Edition Saturday in November:

"Oil and gas production creates a lot of toxic wastewater. To keep it from contaminating drinking water, oil companies inject the fluid into underground disposal wells. That can put pressure on faults, causing them to slip, which scientists say is responsible for Oklahoma's massive earthquake spike."

And even as scientists blame the oil and gas industry for the new seismic activity, "researchers say the earthquakes could compromise the economically vital energy hub."

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