North Texas Quakes

The area around Cleburne, Texas, just south of Fort Worth, has had a flurry of small earthquakes this year, including two last week. None of them has exceeded magnitude 3. Where I live in California, none of this would arouse comment, but most of Texas is as un-seismic as possible. Today's Fort Worth BusinessPress has an article on the subject, and beyond the trite "whole lotta shaking" lead it includes some measured words by geologists. The big question is, are these quakes due to the intensive gas production from hundreds of new wells drilled in Cleburne in the last decade? University of Texas researcher Cliff Froehlich told the paper, "I think most reasonable people with earthquake training probably would say they’re related to the gas production." For a sense of the lay person's outlook, an article in Sunday's Dallas Morning News is worth a read, including the comments section. I detect a lot of denial, wishful thinking and ax-grinding along with generalized concern. But as someone with a geological education and long experience in real earthquake country, I think there is little to worry about in Cleburne beyond the occasional mild shudder.

Triggered earthquakes are likely from the stresses involved in gas production. These are tight shales, and the gas producers are hydrofracturing the rock to open up channels for the gas. The technique injects high-pressure water to crack the shale along with sand to hold the cracks open. Then the gas is bled out. Both fracturing and gas production change the stress patterns in the rock over the long term, and eventually that can tend to trigger small earthquakes.

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Basics of earthquakes
Felt reports from Cleburne, Texas