A record magnitude 4.5 earthquake occurred Monday morning 35 miles north of Dove Creek in Montrose County, according to the U.S. Geologic Survey.
The quake occurred at 10:22 a.m. in a remote area. Its epicenter was about 3 miles southwest of Bedrock along the Lower Dolores River and was a half-mile deep. Two aftershocks, of magnitude 1.9 and 2.0, occurred at 10:41 a.m. and 12:23 p.m., and several others followed.
“It is a pretty strong quake for that area,” said Paul Caruso, a USGS geophysicist.
That area has a history of earthquakes, he said, but they are usually much smaller.
The USGS Felt Report had 695 reports from people who indicated that they felt the quake.
Caruso said the largest number came from the Moab, Utah, area, and quite a few from Grand Junction, Fruita, Monticello and Cortez.
The highest intensity felt was a level 3, enough to knock items off a shelf, he said.
There have been no reported damage or injuries.
The type and cause of the quake was being investigated and whether the nearby brine injection well was connected.
The Bureau of Reclamation operates the 2.9-mile-deep Paradox Valley Salinity Control Facility, a brine injection well along the Dolores River south of Bedrock. The epicenter of Monday’s earthquake occurred about 1 mile southwest of the brine injection well.
The chance of an aftershock of magnitude 3 or higher was listed at 54 percent within the next week, according to the USGS forecast.
The quake occurred in the Paradox Basin within the Colorado Plateau and is the largest recorded for that area, according to the USGS.
The largest previous earthquake was a magnitude 4.4 earthquake in 2000 near the Paradox Valley in Western Colorado and a magnitude 4.3 in 1953 near Green River, Utah. The magnitude 4.4 earthquake in 2000 and many smaller earthquakes in the Paradox Valley were attributed to Paradox Valley brine injection well, part of the a Colorado River Salinity Control Project.
The injected brine fluid is known to cause earthquakes by adding lubrication and pressure to fault lines.
According to a March 4 Reclamation press release, the Paradox Valley brine injection well was not operating at the time of the earthquake because of routine maintenance. But agency spokesman Marlon Duke said that although the well was shut down, pressure would have remained high in the well.
The injection well is part of the Colorado River Basin Salinity Control Program. It is designed to improve water quality in the Dolores River by preventing highly saline groundwater from entering the river.
To accomplish this, brine is extracted from nine shallow wells located within Paradox Valley along the river, then injected deep underground.
From when brine injections began in 1991 to 2014, more than 5,900 likely induced earthquakes have been detected, according to a 2014 report from the Department of Interior.
It is not clear whether Monday’s earthquake was natural or induced, said Don Blakeman, a USGS geophysicist. He said officials are determining whether there would be further study.
Early Monday, the earthquake was reported at magnitudes 4.5, 4.6 and 5.3, depending on the scale used to measure the quake. After further analysis, the University of Utah Seismograph Stations said, USGS settled on magnitude 4.5, using the same “moment magnitude” scale (Mw) that arrived at magnitude 4.6 before the earthquake was downgraded slightly.
The measurement of 5.3 magnitude was derived from the local magnitude scale (Ml), also known as the Richter scale. That scale is no longer used as commonly as the moment magnitude scale.
The area has a low rate of seismicity. Recorded earthquakes have generally been less than magnitude 2. Damaging earthquakes are rare in the western Paradox Basin.
Little or no landsliding was expected from Monday’s quake, but landslides might have occurred in susceptible areas, according to the USGS.
Montezuma County Commissioner Jim Candelaria said the earthquake “shook a table I was sitting at during a meeting” in the county administration building in Cortez.
People reported feeling buildings shake in Towaoc, said Ute Mountain Ute public safety director John Trocheck.
jmimiaga@ the-journal.com
