Study: Daily small quakes raise risk of big ones.

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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.

This once-stable region is now 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 that since Jan. 1, Oklahoma has had nearly 200 quakes that people have felt.

These quakes started to increase in 2008 and made dramatic jumps in frequency in June 2013 and again in...

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