West Texas Quake Strikes Inside Zone Set Up to Curb Wastewater-Linked Tremors

An earthquake that began in far West Texas on Wednesday was felt by residents from San Antonio to Dallas. The magnitude 5.4 tremor was the third-largest the U.S. Geological Survey has recorded in Texas.

Its epicenter fell in an area closely watched by the Railroad Commission of Texas, the state agency that regulates the oil and gas industry. Regulators monitor the region because large volumes of wastewater from fracking are injected underground there, a practice that can induce earthquakes.

Hugh Daigle, an associate professor of petroleum and geosystems engineering at the University of Texas at Austin, discussed the matter with the Texas Standard. He noted that the epicenter lay inside the Northern Culberson-Reeves seismic response area, one of several the commission has created in West Texas. The area is named for the counties where it sits.

According to Daigle, the zone covers ground where many earthquakes are believed to be tied to the disposal of water produced during oil and gas operations. The commission is closely reviewing permits for disposal wells there, with the goal of eliminating earthquakes of magnitude 3.5 or higher within 18 months of the program's start in March of this year.

The boundary was drawn using past data. Between Jan. 1, 2017, and Oct. 20, 2021, the commission logged 42 events above magnitude 3.5, and it outlined the area around their locations. Daigle clarified that the concern is not fracking itself but what companies do with the wastewater afterward.

He explained the mechanism: researchers at the university's Bureau of Economic Geology have mapped a large number of faults that are not currently active. Injecting water raises pressure within the rock, and that change can reactivate such faults and cause an earthquake.

Under the terms of the seismic response program, Daigle said, this quake does not require anyone to take specific action, because no deep injection wells sit close enough to the epicenter. He said it will be interesting to see whether new regulations eventually emerge, but that under current rules no change in behavior appears necessary.

Daigle cautioned that establishing cause is difficult and said detailed studies are likely in the coming months and years. The quake's depth is consistent with being triggered by deep injection wells, he said. The nearest is roughly 9 to 10 miles from the epicenter, and it is not inconceivable that pressure could have traveled that far, though pinning down a single event on such activity is very hard.

Looking ahead, Daigle pointed to the large Valentine earthquake of the 1930s, which struck considerably farther south, and a magnitude 5 quake in the same area in 2020. With hundreds of thousands of barrels, or millions of gallons, of water going down wells there each day, he said it is reasonable to assume the injection affects the subsurface, though much of that process remains poorly understood.