North Texas Earthquake Swarm More Centralized Than Previously Thought


View Earthquakes Near Azle, Texas in a larger map
Map created by Andrew Weber for KUT News and StateImpact Texas. Orange circles represent earthquakes, wavy blue lines represent active wastewater disposal wells.

Another minor earthquake shook the North Texas community of Azle on Monday. It’s one of dozens to hit the region over the last few months that have residents on edge and complaining of property damage.

Many see a link between the quakes and increased oil and gas activity. But challenges confront scientists researching the quakes for the U.S. Geological Survey and Southern Methodist University. For one, they’ve needed to more accurately pinpoint the epicenters of the Azle quakes.

“The closest seismograph station used by the National Earthquake Information Center to locate the Azle earthquakes is over 60 miles to the south, the next closest is 125 miles to the West,” USGS Seismologist Williams Ellsworth explained in a letter to Azle Mayor Alan Brundrett in a December letter obtained by StateImpact Texas (embedded below).

In that same letter, Ellsworth explains how he has produced a more accurate map of the quakes, one that shows them clustered in a more concentrated location than previously thought.

“To date, it looks like the earthquakes are all in one very localized zone,” Ellsworth confirmed to StateImpact Texas over the phone.

The research took into consideration the reporting of residents who physically felt the ground move in the area and then alerted the USGS thought their “did you feel it?” online service.

Azle Mayor Alan Brunrett was disappointed by the Railroad Commissions refusal to provide answers or acknowledge that disposal wells have caused earthquakes elsewhere.

Azle Mayor Alan Brunrett was disappointed by the Railroad Commissions refusal to provide answers at a recent meeting on earthquakes.

“We can take that information, and if they provide us the address, then we know what the shaking was as a function of position,” said Ellsworth. “By making a map of those shaking values we can, rather precisely in this case, pinpoint where the earthquakes had been occurring.”

Ellsworth said residents’ reports show that the quakes were in a much more “localized” zone than the initial seismographic data had placed them. So, when USGS sent more seismographs to the area they knew where to position them.

“We focused our instruments on this zone where people were feeling the earthquakes most frequently and most strongly,” he said, “and indeed that’s borne out our expectation. This is exactly where the earthquakes are occurring.”

The map includes very weak quakes that have taken place since the new instruments have been installed, and does not include any of the quakes that have taken place since the letter was sent. It shows the quakes clustered very tightly together, northeast of the community of Reno.

At a recent public meeting, the Mayor of Reno told state oil and gas regulators that the city’s Town Hall had been damaged by the quakes.

Earthquakes and Oil and Gas Disposal Wells

For decades scientists have understood that injecting liquid into the ground can cause earthquakes. After obtaining the data from Ellsworth, StateImpact Texas overlaid the new quake map with the locations of active disposal wells in the area. The new map shows the quake “swarm” around a mile and a half from one waste water disposal well on Knob Hill Rd. and Lady Bird Lane, and about two miles from another disposal well off Boyd Rd.

There are several other waste water disposal wells in the area visible on the map.

While the link between injection wells and quakes is accepted science, it seems to be something state regulators and many politicians do no like to talk about.  Recently, however, the Texas Railroad Commission, the state agency that regulates the oil and gas industry, has announced that is will hire a seismologist and begin looking into the upsurge in Texas quakes.

 

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