An earthquake shook western Colorado on Monday, the strongest in the state this year, the U.S. Geological Survey reported.
The earthquake hit 4.5 magnitude on the Richter scale at 10:22 a.m. in Bedrock, 35 miles north of Dove Creek near the Utah border.
It happened near Reclamation’s Paradox Valley Salinity Control Facility, where highly pressurized, concentrated salt water — also known as brine — is injected into a 16,000-foot-deep well, “preventing the brine from entering the Dolores River,” says a news release from the U.S. Department of the Interior’s Bureau of Reclamation.
“The well was not operating at the time of the earthquake due to routine maintenance,” the release says. “Operations will not resume until Reclamation completes a thorough assessment of the situation.
“High-pressure brine injection has been known to trigger small earthquakes in the past, and today’s event was within the range of previously induced earthquakes.”
The Dolores River historically picked up an estimated 205,000 tons of salt annually as it passed through the Paradox Valley, the release says.
Since the mid-1990s, much of the salt “has been collected by the Paradox Valley Salinity Control Unit in shallow wells along the Dolores River and then injected into deep subsurface geologic formations.”
The deep-well injection program removes about 95,000 tons of salt annually from the Dolores and Colorado rivers, the release says. The Paradox Valley Salinity Control Facility “substantially benefits downstream water quality in the Colorado River Basin, and helps the United States meet treaty obligations with Mexico for allowable salinity levels in the river.”
Damaging earthquakes are rare in the bedrock in that part of the Colorado Plateau, geologists said.
The biggest there before Monday came in 2000, when brine injections in the Paradox Basin prompted a 4.4 magnitude quake, the USGS website says.
“It was really strange to hear about it, but I didn’t feel it. I haven’t felt one in 20 years,” said longtime Dove Creek resident Roberta Lowry.
The earthquake was the 11th in Colorado this year and the most intense, surpassing the magnitude of the Feb. 27 quake near the Great Sand Dunes National Park and Preserve.
Tremors were felt in western Montrose County, the Sheriff’s Office there said.