A cave-in method of coal extraction called “retreat mining,” recently okayed by regulators for Crandall Canyon, was more likely to have caused the Utah mine disaster than an earthquake, seismographers tell the Los Angeles Times. And they say the massive tremor was consistent with the type “induced by underground coal mining.” It “just doesn’t look like a natural event,” one says.
Still, a quake can't be ruled out, because they do occur at that magnitude in central Utah.
Robert Murray, president of company that operates the mine, insists that there was no retreat mining in the vicinity of the miners. The technique, which involves pulling out pillars made of coal as excavation is finished in an area, is notoriously dangerous; the last pillar to be pulled is nicknamed the "suicide pillar."