HUNTINGTON, Emery County —A new University of Utah study mapped hundreds of aftershocks following the Crandall Canyon Mine collapse — considerably more than previously thought.
The study identified 759 seismic events before the Aug. 6, 2007 mine collapse, and 569 aftershocks that followed. Before this most recent study, researchers knew of about 55 seismic events. Bob Murray, the mine's owner, originally blamed an earthquake for the collapse, but seismograph station data indicated that the mine's collapse is what registered a 4.1 magnitude on seismometers.
The study looked through seismometer records for tremors as small as minus -1: about the amount of energy released by a hand grenade.
"Any understanding we can get toward learning how and why mine collapses happen is going to be of interest to the mining community," said Tex Kubacki, a University of Utah master's student in mining engineering.
A 2008 study by the U. of U. found the collapse area covered 50 acres, but the new study shows that it extended further west than previously thought.
The map, said Kubacki, "helps us better delineate the extent of the collapse at Crandall Canyon. It's gotten bigger."
The new information indicates that tremors mostly occurred in about three areas, rather than the two known areas. In the first area, miners working westward were buried in the mine's initial collapse. In the second, three rescuers were killed in a collapse on the east end. The third, researchers say, was on the very west end of the mine where no miners were working.
"We have three clusters to look at and try to come up with an explanation of why there were three. They are all related to the collapse," said Michael McCarter, co-author of the study and a University of Utah professor of mining engineering.
They identified as many as 1,022 seismic events before the collapse and 1,167 aftershocks, but the evidence of that many events was weak, the authors said.