A 3.8 magnitude earthquake and two smaller aftershocks were recorded Sunday morning south of Bedrock, Colorado, according to the U.S. Geological Survey and University of Utah Seismograph Stations.
The quake occurred at 4:19 a.m. from a depth of about 1.2 miles. Magnitude 2.2 and 2.7 aftershocks were triggered in the same area at 6:32 a.m. and 6:42 a.m. There were no reports of damage.
Bedrock is about 8 miles east of the La Sal Mountains at the Utah state line.
Sunday’s earthquakes near the lower Dolores River were probably caused by the nearby brine injection well of the Paradox Valley Salinity Control Facility, said Jim Pechmann, a seismologist with the University of Utah Seismograph Stations, which tracks regional earthquakes.
“It’s pretty likely it was induced from the saltwater injections,” he said.
On March 4, 2019, a local record 4.5 magnitude earthquake hit in the same area of the injection well, and there were multiple aftershocks. It was also linked to the brine injection facility by seismologists. That quake was felt in Moab, Cortez and as far east as Durango.
After the 2019 earthquake, the Bureau of Reclamation salination injection well facility was temporarily shut down for study about well capacity and the earthquakes. The plant intercepts salty groundwater draining into the Dolores River and injects it 2.9 miles underground to improve water quality in the Dolores River and Colorado River.
But an unintended consequence of pumping briny fluid deep underground has been thousands of human-induced earthquakes.
In April, the plant was restarted, and injection volumes were reduced by a third with the hope that reduced pressure and volume would avoid induced earthquakes.
“The system worked well for a good long time, but there is a limit on how much water you can pump down there,” Pechmann said. “It looks like the fluid has run into a barrier, and is not diffusing away from the well, building up pressure.”
He said the most recent quake likely could be felt in Naturita, to the east. A 3.8 magnitude earthquake could shake items on a shelf or cause minor landslides in already unstable areas, but there were no reports of any such activity Sunday.
A total of 10 earthquakes of magnitude 3.0 or greater have occurred within 15 miles of the epicenter of Sunday’s earthquake since 1997, including a magnitude 3.4 earthquake on Sept. 16, 1997, according to the University of Utah Seismograph Stations.
When engineers installed the Paradox Valley Salinity Control project in 1996 on the lower Dolores River, the result was improved water quality in the nearby Colorado River and for millions of people and farms downstream.
In December, the Bureau of Reclamation released a Draft Environmental Impact Statement analyzing alternatives for continued salinity control at the location.
“Because the underground reservoir pressure and induced seismicity have increased, and brine disposal rates have had to be substantially reduced in response, a new brine control and disposal facility is needed,” it said.
The facility has intercepted and injected about 95,000 tons annually of brine into the injection well.
The injected brine fluid is known to cause earthquakes by adding lubrication and pressure to fault lines. An estimated 6,000 mostly smaller earthquakes are thought to be caused by the Paradox injection well since the 1990s, according to government reports and seismologists.