Almost a day after a devastating 3.9 magnitude seismic event trapped six miners inside the Crandall Canyon Mine, another event measuring 1.0 on the Richter scale was recorded near the Aberdeen Mine more than 30 miles away.
The minor seismic event, about six miles northeast of Helper, was recorded at 2:31 a.m. Tuesday. Seismologists believe it is consistent with mining operations in Utah's coal country.
"We see these events on a daily basis," said Relu Berlacu at the University of Utah Seismograph Stations. "If you look at the distribution of earthquakes in the area, you'll see this tendency of clustering around where the mines are. Most of them are generated by the mining itself."
A check of recent earthquakes recorded in the area shows a cluster of small quakes around the mines. Seismologists say some of them may be natural earthquakes, but many of them are a result of mining.
"That area is known as the coal mining seismic belt," said Dave Tabet, the energy and minerals program director for the Utah Geological Survey. "The way they're mining, they're always setting off seismic events."
Other scientists agreed.
The seismic waves in the area of the mine were similar to those caused by a collapse and not an earthquake, said Rafael Abreu, a geologist with the U.S. Geological Survey's National Earthquake Information Center in Golden, Colo.
"What we seem to see from the data we're looking at, we're seeing a mine collapse," he told the Deseret Morning News.
He based that on reading of the seismic waves, as well as a review of the geological area. While the conclusion is not final, Abreu said the initial seismic event and the "after events" were likely caused by the mine collapse.
Rescuers trying to reach the trapped miners are having to deal with seismic problems inside the Crandall Canyon Mine.
"There has been seismic activity," Assistant Labor Secretary Richard Strickler said. "Bumps, movements of the mountain. This puts a safety hazard to the rescue workers."
A pressure-shifting "bump" inside a mine shaft forced rescuers to leave the mine early Tuesday. At 2:43 a.m. Tuesday, a 1.6 magnitude event was registered in the same general area as the one that trapped the miners. Others ranging from 1.2 to 2.2 on the Richter scale were recorded in the general area Monday night and early Tuesday.
Abreu said they recorded another event at 3:42 p.m. Tuesday measuring 1.7 in magnitude.
University of Utah seismologists said the seismic events being recorded could be linked to the mine collapse.
"The events could be part of the background seismicity," Berlacu said. "They could be related to the main event."
The cause of the mine collapse in Crandall Canyon has been the subject of heated debate. The mine company's president, Bob Murray, angrily denied that mining caused it at two news conferences Tuesday.
"This was caused by an earthquake," Murray told reporters. "It was a natural disaster."
Murray held up a University of Utah Seismograph Stations report he says proves his stance. He said the epicenter of the 3.9 magnitude quake was too far away from where the miners are located to say that a mine collapse caused it.
Many of Utah's mines are close to fault lines. Some dig right up to them or even around them. The Crandall Canyon Mine is close to the Joe's Valley fault line, but Tabet said that fault hasn't been active within historic times.
"Most of the mines in the Wasatch Plateau intersect faults, and they have to mine up or down to get past," he said.
University of Utah seismologists said Tuesday they were still investigating, but preliminary results seemed to point to the mine collapse causing the seismic event in Crandall Canyon.
Mine officials have said that the earthquake was about 5,000 feet from where the miners are trapped. Scientists have suggested the quake could have hit at the mine level but said more research is needed. The National Earthquake Information Center said the seismic event did not have the characteristics of a typical quake, including the waves that an earthquake generates.
State seismologists have authored several studies on seismic events caused by mining activities in Emery and Carbon counties. Historically, some events have been recorded at 4.0 on the Richter scale."We have natural earthquakes too, in the area," Berlacu said. "Not all the events are mining-induced events, but most of them are."
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