To no one’s great surprise, scientists have linked the elevated seismic activity in Oklahoma to increased oil and gas exploration, especially hydraulic fracturing (a/k/a tracking). From the Independent:
Between 1975 and 2008, Oklahoma recorded an average of no more than six earthquakes per year, yet now it is the second most seismically active of the contiguous United States, beaten only by California. Scientists have linked this surge in seismic activity to a parallel increase in oil and gas exploration, including fracking.
In 2009, there were almost 50 quakes in Oklahoma. The following year, that number leapt to more than 1,000. Most were not “felt” earthquakes – those of magnitude 2.5 and above, which can be detected by humans. However, the state’s annual record of 222 felt quakes, set in 2013, has already been broken this year, with 253 so far. Seismologist Austin Holland of the Oklahoma Geological Survey told Reuters: “We have had almost as many magnitude 3 and greater already in 2014 than we did for all of 2013… We have already crushed last year’s record for number of earthquakes.”
Earthquakes rarely cause damage unless they are of magnitude 4 or higher.