Earthquakes at AZLE USGS map

Dots mark the location of the latest earthquakes NW of Fort Worth. (USGS)

A fresh bevy of earthquakes — about 32 and counting — north of Fort Worth has rattled area residents over the past two months.

At a recent town meetings in the exurb of Azle, northwest of D/FW, residents were hopping mad about cracks in buildings and sink holes in their yards, which appeared after an outbreak of earthquakes in December and early this month.

The latest earthquake, just days ago, was a 3.1 magnitude, still small as earthquakes go but on the larger side of the freak mini-quakes that have been associated with gas drilling activity in Texas, Oklahoma, Arkansas, Ohio and a few other places of historical geologic stability.

How and why these earthquakes happen is not well understood, though it makes commonsense: Turn the earth into swiss cheese and things start to shift around.

Lately, scientists have been trying to put a finer point on it. Studying the quakes in areas of dense drilling, they’ve found a correlation between the shaking and the inevitable waste injection wells where drillers dump the “produced” water that was expended on the fracking process. The EPA allows gas companies to deep-six their toxic waste in the earth, apparently for lack of a way to get it to the moon.

We found this video by NPR’s State Impact helpful in understanding this phenomenon:

In 2012, UT research scientist Cliff Frohlich, reported that his study of earthquake epicenters and injection well sites found that most earthquakes in North Texas’ Barnett Shale occur within a few miles of one or more injection wells.

“You can’t prove that any one earthquake was caused by an injection well,” Frohlich said. “But it’s obvious that wells are enhancing the probability that earthquakes will occur.”

In addition, Frohlich found that the wells nearest to the eight earthquake groups he studied were being used as the highest injection rate, with maximum monthly totals exceeding 150,000 barrels of water.

None of the earthquakes reviewed (occurring in 2009-2011) were ranked as 1.5 to 2.5 on the Richter Scale, not large enough to cause any harm to the public.