How did wastewater injections cause 1,971 earthquakes near Pecos this year

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Although there is no way to distinguish between natural and induced earthquakes, experts agree that the dramatic increase in seismic activity near the Pecos is likely the result of wastewater injections into disposal wells.

In fact, most geologists believe that wastewater injection is the primary cause of induced earthquakes, according to Daniel Trogman, associate professor of geological studies and head of the Seismology Laboratory at the University of Texas at Austin.

“There are various mechanisms by which humans can cause earthquakes, and wastewater injection is probably the most obvious and common in West Texas,” he said.

Wastewater, or salt water, is a byproduct of oil and gas production that oil companies dispose of by injection deep into the ground, usually near drilling sites. When this fluid is injected near faults, or cracks in the Earth’s crust, it can sometimes cause these faults to slide and create earthquakes.

“When you inject a fluid into the Earth’s interior, it changes the state of the Earth’s pressure, and this will tend to activate faults that are already there,” said Mary Leatherland, director of the New Mexico Tech Seismological Observatory.

Trogman said induced earthquakes may have occurred before the last dumping of sewage, but it’s possible that over the past decade humans began causing most earthquakes in that area.

Data provided by the USGS shows that there were no earthquakes in the Pecos region in 2010. Since the beginning of this year, there have been 1,971 earthquakes of magnitude 1.5 or higher in that region.

This is a significant increase from just last year (227 earthquakes) and in 2019 (97 earthquakes). Experts said the buildup of injected fluid beneath the surface likely caused the rocks to remain in a stressful state and led to more seismic activity.

And while most of the nearly 2,000 earthquakes this year had a magnitude of 2.5 or less, there were 86 recorded as above 3.0 — including one with a magnitude of 4.2 on Friday morning — compared with 12 earthquakes greater than 3.0 in 2018.

Part of the reason the total number of earthquakes has risen over the past few years, Leatherland said, is that there is better equipment that can detect 1.0 or 2.0 earthquakes. But it said an increase in earthquakes of 3.0 and above indicates that oil activity is affecting earthquakes in the region.

The height of small earthquakes is likely a sign of larger earthquakes, according to Letherland. She pointed to Oklahoma, where oil and gas activity has caused more major earthquakes in the state than those experienced in California from 2014 to 2017.

“That’s the main concern – as we’re seeing more of these small earthquakes, we want to make sure that they’re not progressing toward the bigger ones,” Leatherland said.

After production activity caused four of the five largest earthquakes in Oklahoma’s history, the state introduced new regulations that reduced injections by 40 percent. Trogman said earthquakes in Oklahoma have fallen to a more manageable level since these new rules went into effect several years ago.

“We are less likely to see bigger events, and they (earthquakes) are definitely less disruptive than they were five years ago,” he said.

Trogman said the magnitude and frequency of earthquakes near Pecos show that it is “only a matter of time before something fairly serious happens.”

“Trying to find a balance between the risks to the population and the risks to economic production, I think, is something that should be taken very seriously at this stage,” he said.

The Texas Railroad Commission introduced rules in 2014 limiting the amount of injection fluid to 30,000 barrels per day, according to spokesman Andrew Keys. He said that the rehabilitation center has received 959 requests to dispose of wells in areas with historical earthquakes since the regulations came into force, and among these requests, 627 permits were issued with conditions and 218 requests were returned or withdrawn.

“The Railroad Commission’s top priority is to protect public safety and the environment, and our employees continue to enforce some of the strictest regulations in the country on well disposal in earthquake zones,” Casey said in a statement.

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