EARTHQUAKES:

USGS sending instruments to record Texas quakes

The U.S. Geological Survey is sending four seismic recorders to Texas to record activity in an area where local leaders worry that drilling processes are causing earthquakes.

The portable recorders are to be deployed around the town of Azle by scientists from Southern Methodist University, said Bill Leith, senior science adviser for earthquake and geologic hazards at USGS.

People in and around the bedroom community northwest of Fort Worth have been shaken by 19 small earthquakes in the past month. The strongest was a magnitude-3.6 quake Nov. 20.

There have been no injuries and no reports of serious property damage, but the shaking has unsettled many residents (EnergyWire, Dec. 5.

Azle Mayor Alan Brundrett and Parker County commissioners have said they want oil and gas officials at the Texas Railroad Commission to see if the earthquakes are being caused by nearby injection wells used to dispose of wastewater from hydraulic fracturing and drilling.

Commission inspectors have examined one well and found it in compliance with the rules. But the rules don't address injection wells causing earthquakes.

Seismologists say the first step in figuring out whether the earthquakes are man-made would be getting more accurate locations for the epicenters of the quakes. The closest monitoring instrument is about 60 miles from Azle, so the locations being provided by USGS aren't very precise.

Leith said USGS will be working with SMU professors Brian Stump and Heather DeShon. Stump has studied earthquakes in North Texas for years.

Leith said the portable recorders are the same type that were sent to Timpson, in East Texas, where they "have provided invaluable data for understanding the connection between the earthquakes that occurred there in 2012 and 2013 and the nearby wastewater disposal wells."

After an earthquake in May 2012, seismologists from the University of Texas, Austin, and Stephen F. Austin State University started studying whether it and other rumblings could be linked to drilling and injection. At magnitude 4.8, the 2012 quake was the largest quake ever recorded in East Texas (EnergyWire, Sept. 4).

Their findings, reported earlier this year at a conference of the Seismological Society of America, were that "it is possible the Timpson earthquakes were induced by injection."

But the scientists also noted that a smaller earthquake associated with a fault system was reported in 1981 about 15 miles away.

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