Study: Oklahoma's daily small quakes raise risk of big ones

SAN JOSE, California -- Small earthquakes shaking Oklahoma and southern Kansas daily and linked to energy drilling are dramatically increasing the chance of bigger and dangerous quakes, federal research indicates.

The once-stable region now is just as likely to see serious damaging and potentially harmful earthquakes as the highest-risk places east of the Rockies, such as New Madrid, Missouri, and Charleston, South Carolina, which had major quakes in the past two centuries.

Still it's a low risk, about a 1 in 2,500 years' chance of happening, according to geophysicist William Ellsworth of the U.S. Geological Survey.

"To some degree, we've dodged a bullet in Oklahoma," Ellsworth said after a presentation to the American Association for the Advancement of Science.

But, he added, "This is not to say we expect a large earthquake tomorrow."

During the 90-minute session on human-induced earthquakes, three quakes larger than 3.1 magnitude hit northern Oklahoma. Federal records show since Jan. 1, Oklahoma has had nearly 200 quakes people have felt. These quakes started to increase in 2008 and made dramatic jumps in frequency in June 2013 and again in February 2014, Ellsworth said.

They are mostly in areas with energy drilling, often hydraulic fracturing, a process known as fracking. Many studies have linked the increase in small quakes to the process of injecting wastewater deep underground because it changes pressure and triggers dormant faults.