Although there has been occasional earthquake activity in that region long before fracking, that does appear to be what they’re going to blame it on.
From accuweather.com, Nov 13, 2014...
Frequent, rumbling tremors beneath the earth may be a common occurrence in California, but Oklahoma has now surpassed the state in the number of earthquakes felt this year - a trend that is surprising geophysicists and raising concern.
“It is actually very surprising to us as well,” Pasadena, California-based U.S. Geological Survey Geophysicist Elizabeth Cochran said in July.
Between 1975 and 2008, only an average of two earthquakes with a magnitude of 3.0 or greater would occur each year in Oklahoma.
Changes in pressure near faults in Oklahoma that surpass the fault’s critical pressure threshold are likely the cause of the seismic activity surge.
The cause for this increase does not appear to be natural and has likely been induced by fluid injection, part of the crude oil and gas industry’s disposal of wastewater through the creation of wastewater wells.
The injection of wastewater fluids deep into the ground can lubricate existing, dormant faults and change the stress and pressure of the fault, leading to increased seismic activity, Cochran said.
“These quakes tend to be shallower,” she said. “At this point, we do not think this is a natural variation.”
The largest event in Oklahoma to occur in the past century was a 5.6-magnitude quake that struck in November 2011.
“That was the largest event linked to injection,” Cochran said.
With the growing number of quakes in the region, the hazards associated with an even larger event occurring near a major metropolitan area are raising eyebrows among geophysicists.
“That is our big concern,” Cochran said.
http://www.accuweather.com/en/weather-news/breaking-rare-48-earthquake-ru/37271020
Oklahoma had quakes like they having now from the 1950s into the early ‘60s. Then it quieted down.
That's quite a few at least compared to Michigan. Who's to say that this fault line didn't become more active?