Steamboat Springs The mild earthquake detected by the U.S. Geological Survey before dawn Saturday near the Twentymile Mine in western Routt County was apparently just that.
The USGS reported a magnitude-2.5 quake at an estimated depth of 3.1 miles about 12 miles west/southwest of Steamboat Springs. The latitude and longitude for the tremblor placed it within about a 4-mile diameter of the large underground coal mine with a horizontal margin of error of plus or minus 7.5 miles.
The last time the USGS reported a small earthquake in that vicinity March 30, the cause of the seismic activity proved to be the settling of a column of coal supporting the ceiling of a mine shaft.
However, that was not the case this time, according to mine owner Peabody Energy and the federal agency that overseas mine safety.
“I talked to mine officials and there was nothing,” Peabody spokeswoman Meg Gallagher said Monday. “Twentymile Mine is operating normally. We don’t know the reason for the seismic activity.”
Amy Louviere, public affairs director for the Mine Safety Health Administration in Washington, D.C., said her agency’s officials in Denver had been in touch with Twentymile officials.
“According to the MSHA district office in Denver, the mine was contacted, and they claim they did not notice anything amiss as a result of an earthquake,” Louviere wrote in an email.
Circumstances were different in late March and early April when the mine temporarily ceased operation of its longwall mining activity but continued extracting coal by other means while the U.S. Mine Safety Health Administration collaborated with mine operators and owner Peabody Energy to stabilize the situation.
State geologist Vince Matthews told the Steamboat Pilot & Today at the time that a naturally occurring earthquake was a possibility given that several geologic faults cut across the area known as Twentymile Park. However, he contacted geologists at the mine March 30 because the depth of the 2.8 magnitude was just 0.62 miles, suggesting it could have been related to mining activity.
Saturday morning’s earthquake was deeper — an estimated 3.1 miles.
Allyn Davis, Mine Safety Health Administration district manager in Denver, said in April that the March accident sounded worse than it was.
It involved the “compression” of coal pillars that are relied upon to support the ceiling of the underground mine. At the same time the pillars compressed, a roof fall took place, partially blocking the tail end of the longwall, which serves as an exit point for miners, he said.
— To reach Tom Ross, call 970-871-4205 or email tross@SteamboatToday.com