A swarm of earthquakes has been plaguing Oklahoma thisweekend. The quakes started with small tremors about 2.7 magnitude and increasing to a record-breaking 5.6 magnitude quake that struck at 10:53 pm CST. That quake was centered near Sparks, about 40 or so miles northeast of Oklahoma City, and felt as far away as St. Louis and parts of Texas.
Oklahoma is no stranger to earthquakes – the state typically has about 50 shakers a year. But the number has increased dramatically in the last three years, with more than 1,000 earthquakes reported in 2010. Earthquakes tend to occur at the edges of tectonic plates – but Oklahoma is located securely in the middle of a tectonic plate, and there aren’t many faults.
While researchers can’t say for sure why Oklahoma is experiencing an increase in earthquakes, some people are wondering whether the tremors are related to hydraulic fracturing. The area lies above the Woodford Shale, and in the past couple of years energy companies have drilled more than 1500 wells using hydro-fracking to break the rock.
The Oklahoma Geological Survey has studied whether the quakes in 2010 could have been caused by fracking. Their report, dated August 2011, is still under review, so it’s not official yet. But you can read it here.
Meanwhile, earlier this week Cuadrilla Resources, a British energy company, recently admitted that its hydraulic fracturing operations likely triggered “a number of minor seismic events” that shook the UK this spring.
And last spring an earthquake swarm around Guy, Arkansas was thought to be due to injection of drilling wastes into underground wells.