Located in the middle of the country, far from any major fault lines, Oklahoma experienced 585 earthquakes of magnitude 3.0 or more last year. That is more than three times as many as the 180 which hit California last year. “It’s completely unprecedented,” US Geological Survey seismologist George Choy said. As of last month, Oklahoma has already experienced more than 600 earthquakes strong enough to rattle windows and rock cars. The biggest was a magnitude 4.5 earthquake that hit the small town of Crescent. Sandra Voskuhl, 76, grew up in the rural oil boomtown and said she has never felt the earth shake like it did on July 27.
First came a thunderous boom. Then the red earth shook hard, Voskuhl said. “You heard it coming,” she said. “Everything shook.” She recalled screaming as framed pictures toppled over in her home. Then, when things got quiet, she drove over to the town’s Frontier Historical Museum to help clean up antique dishes that had crashed to the ground and shattered. “We need the oil for our workers and our economy,” she said. “But these earthquakes are a little scary,” Voskuhl said.
Hydraulic fracturing — or fracking — is the process of shooting water mixed with sand and chemicals deep into the earth to crack rock formations and bring up oil and natural gas trapped inside. The process has unlocked massive amounts of oil and gas in Oklahoma and other US states over the past decade. However, along with the oil and gas comes plenty of that brackish water, which is disposed of by injecting it into separate wells that are dug just less than 2km deep. The unnatural addition of the water can change pressure along fault lines, causing slips that make the earth shake, Choy said.
There is debate among scientists over how large of a fault could be awakened and how hard that fault might shake. One camp believes Oklahoma is unlikely to see bigger than a magnitude 4.0 to 5.0 earthquake, which would be enough to break windows and knock things off shelves. Others believe a magnitude 7.0 earthquake could come about, which would be strong enough to topple buildings. “What’s at risk is that when you put water into the ground, it’s never going to come back out. You’re putting it in places it has never been before,” Choy said. “The bigger the volume, the greater the area will be affected. And we don’t know what the long-term effect will be,” he said.
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