Austin Holland, a research seismologist, looks over data at the Oklahoma Geological Survey in Norman, Okla., Nov. 26, 2013. Residents and officials in the state are worried by a dramatic uptick in minor earthquakes, which some scientists link to the thousands of wastewater disposal wells used by the state's key oil and gas industry.

Nick Oxford, New York Times

2,600 earthquakes rattle Oklahoma; oil industry to blame?

  • Article by: HENRY FOUNTAIN
  • New York Times
  • December 12, 2013 - 8:25 PM


– Mary Catherine Sexton has been rattled enough.

This fall her neighborhood here has been shaken by dozens of minor earthquakes.

Even before a magnitude 4.5 quake Saturday knocked objects off her walls, Sexton was on edge. “Our kids are scared. We’re scared,” she said.

Oklahoma has a yearly average of about 50 tremors, almost all of them minor. But in the past three years, the state has had thousands of quakes. This year has been the most active, with more than 2,600 so far, including 87 last week.

While most were too slight to be felt, some, like the quake Saturday and one in November, have been sensed over a wide area and caused damage. In 2011, a magnitude 5.6 quake — the biggest ever recorded in the state — injured two people.

State officials say they are concerned, and residents are talking about buying earthquake insurance. “I’m scared there’s going to be a bigger one,” Sexton said.

Just as unsettling in a state where more than 340,000 jobs are tied to the oil and gas industry is what scientists say might be causing many of the quakes: the practice of disposing of billions of gallons of wastewater, produced along with oil and gas, by injecting it under pressure into wells that reach permeable rock formations.

“Disposal wells pose the biggest risk,” said Austin Holland, a seismologist with the Oklahoma Geological Survey.

Oklahoma has more than 4,000 disposal wells.

“Could we be looking at some cumulative tipping point? Yes, that’s absolutely possible,” Holland said, but there could be other explanations.

Scientists have known for years that injection wells can induce earthquakes by changing pressures underground.

Hydraulic fracturing, or fracking — injecting liquid at high pressure into shale rock — causes small tremors as rocks break, releasing oil or gas.

Fracking has been linked to minor quakes in Oklahoma, England and British Columbia.

A greater potential concern, scientists said, is wastewater disposal. Disposal wells linked to quakes have been shut down in some states, including Arkansas and Ohio.

Along with oil and gas, water comes out of wells. Because transporting water is costly, disposal wells often are nearby.

The oil and gas industry points out that many of Oklahoma’s disposal wells are in areas with no earthquake activity, and that injecting wastewater has been going on for years.

“We’ve been doing this for a long time and it hasn’t been an issue before,” said Chad Warmington, president of the Oklahoma Oil and Gas Association.

State regulators are concerned, but cautious.

“We have to look at what data and scientific evidence supports some connection,” before taking steps to manage the risk, said Dana Murphy of the Oklahoma Corporation Commission.

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