Study ties oil, gas production to Midwest quakes


Oil and gas production may explain a sharp increase in small earthquakes in the nation's midsection, a new study from the U.S. Geological Survey suggests. Outside experts were split in their opinions about the report, which is not yet published but is due to be presented at a meeting later this month.

The study said a relatively mild increase starting in 2001 comes from increased quake activity in a methane production area along the state line between Colorado and New Mexico. The increase began about the time that methane production began there, so there's a "clear possibility" of a link, says lead author William Ellsworth of the USGS.

There has been concern about potential earthquakes from a smaller-scale injection of fluids during a process known as hydraulic fracturing, or fracking, which is used to recover gas. But Ellsworth said Friday he is confident that fracking is not responsible for the earthquake trends his study found, based on prior studies.

Magnitude 3 quakes are mild, and may be felt by only a few people in the upper floors of buildings, or may cause parked cars to rock slightly. The biggest counted in the study was a magnitude-5.6 quake that hit Oklahoma last Nov. 5, damaging dozens of homes. Experts said it was too strong to be linked to oil and gas production.

The idea is to understand how the man-made activity triggers quakes, she said. One possibility is that the injected fluids change the friction and stickiness of minerals on fault lines. Another concept is that they change the below-surface pressure because the fluid is trapped and builds, and then "sets off something that's about ready to go anyway," Lohman said.



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