Scientists See Quake Risk Increasing in Oklahoma

A sharp rise in the number of earthquakes in Oklahoma, apparently related to underground disposal of wastewater from oil and gas production, has significantly increased the chances that a damaging quake will occur there, federal and state scientists say.

Already this year there have been 145 small earthquakes of magnitude 3.0 or higher in the state, compared with 109 for all of 2013, the scientists with the United States Geological Survey and the Oklahoma Geological Survey said in a statement Monday.

The quakes, largely in the central and north-central parts of the state, have rattled nerves but caused little damage. But the increase makes it more likely that a quake of magnitude 5.5 or higher could occur, the scientists said, although they did not quantify the increased risk.

They said they were issuing the advisory so that it might become a “crucial consideration in earthquake preparedness for residents, schools and businesses.” Of special concern, they said, were older masonry structures, which could be heavily damaged by earthquake shaking.

The state has had two moderate quakes of magnitude 5.5 or higher in its history, including a 5.6-magnitude temblor in 2011 that injured two people and damaged about a dozen homes, some beyond repair, about 45 miles east of Oklahoma City. For three decades until 2009, Oklahoma averaged only two quakes a year of magnitude 3.0 or higher.

An analysis of recent activity in Oklahoma and Arkansas by United States Geological Survey scientists, published last year, found that the increased quake activity was probably not a result of random fluctuations. A more likely culprit, the scientists said, was “a significant change in the underlying triggering process.” Injection of wastewater from oil and gas production into deep disposal wells is known to induce earthquakes by changing pressures around faults underground. Oklahoma has about 4,000 such disposal wells.