Chase Woodruff

(Colorado Newsline) One of the largest earthquakes to hit Colorado in decades rattled homes and businesses near Trinidad on the night of March 9, one of a series of six small quakes that were detected in western Las Animas County, not far from the Colorado-New Mexico border.

The area known as the Raton Basin has seen a significant increase in seismic activity since 2001, a surge that scientists attributed to nearby natural gas production and its associated waste injection wells, which pump tens of millions of gallons of water produced each year as a byproduct of gas extraction back into the Earth’s crust.

“I think it’s highly likely that these earthquakes were induced by the wastewater disposal operations in the area,” Justin Rubinstein, a research geophysicist with the U.S. Geological Survey, said in an interview.

Rubinstein was the lead author of a 2014 USGS study that found that wastewater injection was “responsible for inducing the majority of” Raton Basin seismicity over the preceding 13 years. Other studies, including several from researchers at the University of Colorado Boulder, have reached similar conclusions, and “induced seismicity” from injection wells and other oil and gas operations has been observed in other states like Oklahoma and Kansas.

Only a single earthquake with a magnitude of 4 or greater was recorded in the Raton Basin between 1972 and July 2001, the USGS study noted, compared to 12 recorded between August 2001 and 2013. Large volumes of produced water began to be injected in the area in 1999.

The Colorado Oil and Gas Conservation Commission, the state agency that regulates drilling and injection wells, adopted its first-ever rules to evaluate the risk of induced seismicity as part of a broader overhaul of drilling regulations approved in 2020.

“COGCC is aware of the seismic events that recently took place in the Raton Basin,” an agency spokesperson said in a statement. “In accordance with COGCC’s risk-based seismic hazard mitigation approach as it pertains to injection wells, COGGC has discussed applicable strategies with the relevant operators, and will continue to take appropriate steps as needed.”

Since the late 1990s, parts of the Raton Basin in both Colorado and New Mexico have been significant producers of coalbed methane, a kind of natural gas found in coal deposits. Extracting coalbed methane often requires pumping large volumes of dirty, salty water out of the ground as a byproduct, then returning it even deeper underground via injection wells.

“These fluids, they propagate to a preexisting fault in the area,” Rubinstein said. “And it’s easier for that fault to slip. A good analogy is an air hockey table — the puck doesn’t move very easily when the air is off, (but) the air turns on and the puck moves very easily. That is exactly what is happening in this case.”

Modeling ‘stress fields’

Colorado has a long history with induced seismicity, beginning with liquid waste injections undertaken at the Rocky Mountain Arsenal chemical weapons plant in 1962. A series of earthquakes triggered by those injections included a magnitude 4.8 that caused over $1 million damages in Denver.

Kyren Bogolub, a seismologist with the Colorado Geological Survey, said it’s not always possible to definitively attribute an individual earthquake to wastewater injection, but scientists are making strides in understanding how to mitigate risks in the long run.

“There are researchers that do modeling that looks at the stress field underneath the subsurface,” and they’ll say, given what we know about the geology and the stress field in this area, how is that going to change if we start injecting this many gallons of water per month?” Bogolub said. “Is that change in the stress field enough to cause earthquakes.”

“It does depend a lot on the area,” she added. “There’s plenty of areas where we inject gallons and gallons and gallons of water and don’t cause any earthquakes at all. And there are other areas where you just inject a little bit and you trigger magnitude 4s. … It’s really important to study these things on a very local level.”

Have a plan

While the COGCC noted that USGS earthquake data indicated that last week’s earthquake “occurred much deeper in the Earth’s crust than any injection activity in the area,” Rubinstein said the depths recorded are consistent with plenty of other induced quakes.

“We’re looking at earthquakes that are a mile, two miles, five miles deep,” he said. “That is totally within the realm of reasonability that a fluid injection could be causing these.”

Colorado’s most powerful seismic event in the last 50 years was a 5.3 magnitude earthquake in the Raton Basin southwest of Trinidad in 2011, and USGS research found “clear evidence” that the event was caused by fluid injection. No injuries were reported, but residents in Trinidad and other Las Animas County towns reported damages estimated in the hundreds of thousands of dollars.

The largest quake known to have been induced by fluid injection was a magnitude 5.8 event in Oklahoma in 2016. Rubinstein said that while it’s difficult to predict the Raton Basin’s seismic future, Coloradans living in the area would be wise to plan ahead for the possibility of more damaging events.

“People in this area need to start thinking about how they’re going to respond in the case of a damaging earthquake,” he said. “That’s having an earthquake kit, having a plan of how you’re going to reconnect with your loved ones, et cetera.”