U researchers have been insisting that the Crandall Canyon Mine collapse was not triggered by an earthquake, and now they have a study to prove it.
The study, released Monday, described the nature of the collapse, which debunks several misconceptions. The collapse was not caused by an earthquake, it did not last several minutes, and the original shocks occurred 0.6 mile from where seismologists first placed them.
Rescue missions were sent to search for the six lost miners after the collapse, but mine officials recalled them after rescuers were injured and killed during attempts. Families were concerned that the trapped miners might have spent time trying to escape.
However, the study indicates that the collapse occured within seconds.
“I’m sure it was over before they knew what was going on,” said Jim Pechmann, lead author of the study and research associate professor of geology and geophysics at the U. “There certainly wasn’t any time to get out of the way.”
Pechmann said that when the first shocks arrived on the morning of Aug. 6, he and his colleagues knew the collapse couldn’t be an earthquake. The 3.9 magnitude shocks the researchers discovered were from the mine and gave further proof to their suspicions.
A study completed by University of California, Berkeley, confirmed that idea. The pillars supporting the roof exploded and shattered, said Walter Arabasz, the U’s director of seismology studies. The large amounts of coal fragments filled up the mine’s open spaces. This caused the roof of the mine to drop about a foot.
The collapse filled an area 3,018 feet long and 722 feet wide in no more than a few seconds, according to the study.
The misunderstanding that the collapse lasted several minutes all started from a rumor, Pechmann said.
“People who looked at our website and saw the shock lasted four minutes, (they thought) then the collapse must have lasted four minutes,” he said. “Any seismologist will tell you that’s not true. The seismic waves can last for hours, even days.”
The researches formed the study after months of gathering information about the collapse from temporary instruments, station data and accident reports. They also used a new technique known as double difference, which compares aftershock arrival times to determine where the original shock came from.
The 53-page study was submitted to the Mine Safety and Health Administration and will be important to its investigation into the cause of the collapse, Arabasz said. It might also shed light on how to prevent future collapses, he said.
The site used a method called retreat mining, in which pillars of coal are used to hold up the roof. When an area has been cleared, the pillars are removed and the roof is allowed to collapse in that zone. It is a risky method, and the collapse might have been prevented had it not been used, Pechmann said.
Mine co-owner Robert Murray, who insisted that the collapse was the result of an earthquake and could not be avoided, said he would not comment on the study. At the time, Murray insisted that no retreat mining was going on in the miners’ vicinity.
Three other authors contributed to the study including Kris Pankow, research associate professor of geology and geophysics; Relu Burlacu, network manager for the U Seismograph Stations; and Michael McCarter, chairman of the U mining and engineering department.
Lennie MahlerMark Hale, earthquake information specialist at the U seismograph center, points out seismic activity around the Crandall Canyon Mine collapse last August.