WASHINGTON — The natural gas industry uses hydraulic fracturing, called fracking, in which millions of gallons of water, sand and chemicals are injected deep underground to break up rock.
While that may sound like it could cause an earthquake, the typical energy released in tremors triggered by fracking “is the equivalent to a gallon of milk falling off the kitchen counter,” Stanford University geophysicist Mark Zoback said.
The magnitude-5.6 quake that rocked Oklahoma three miles underground had the power of 3,800 tons of TNT, which is nearly 2,000 times stronger than the 1995 Oklahoma City bombing.
In Oklahoma, home to 185,000 drilling wells and hundreds of injection wells, the question of man-made seismic activity comes up quickly. But so far, federal, state and academic experts say readings show that the Oklahoma quakes were natural.
“There's a fault there,” U.S. Geological Survey seismologist Paul Earle said. “You can have an earthquake that size anywhere east of the Rockies. You don't need a huge fault to produce an earthquake that big. It's uncommon, but not unexpected.”
But there's a reason people ask whether the quakes are man-made rather than from the shifting of the Earth's crusts.