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Aug 9, 2007 8:56 am US/Mountain
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Did An Earthquake Cause The Mine Collapse?
by Alan Gionet
GOLDEN, Colo. (CBS4) ―
The U.S. Geological Survey's Earthquake Information Center has been a busy place lately. They've been fielding calls that go something like this: "Was it or wasn't it?"
Right now the answer is: it wasn't. The question is: "Did an earthquake cause the mine collapse?"
The part-owner of the Crandall Canyon Mine in Utah, Bob Murray, has been insisting since Monday that the mine collapse that trapped six workers was initiated by an earthquake.
"This whole problem has been caused by an earthquake," he said.
It has come during news briefings about the efforts to reach the miners. They are briefings in which Murray has been asked whether the collapse might have been caused by the controversial practice known as "retreat mining."
Pillars of coal are left supporting a ceiling until those supports are pulled and then mined. It's an intentional collapse. Murray has said over and over that the 3.9 magnitude event measured at 2:48 a.m. Monday was an earthquake that caused the cave-in. He also denied that retreat mining was being used.
At the USGS office in Golden, Colo., things aren't adding up for geophysicist Stuart Sipkin.
"These just don't look like the seismograms that a regular tectonic earthquake would create," he said, looking at the waves recorded by monitoring stations. "Earthquakes tend to occur on, slip on a fault and this was actually, this mine collapse was a cavity closing up."
The waves start as rumblings, then increase. But not at the rate of a typical earthquake, Sipkin said.
"The frequencies involved are much more long period," he said. "It's lacking in a lot of different frequencies. The seismogram looks like it's just sort of rumbling along, instead of starting off like this where it just sort of starts rumbling along, it would be much sharper."
He compared the difference to a bang in an earthquake. There's no evidence of that.
Murray has said the depth of the epicenter was far below his miners. But that was early data.
Newer, more refined estimations now put it about a kilometer below the surface, much closer to the miners.
The more the experts study the data, Sipkin said, the more certain he is that there was no earthquake trigger.
"All of the info seems to be much more consistent with a mine collapse," he said.
Sipkin said he can never be 100 percent sure. He said of Murray's claims, "If he's insisting that he has evidence that it is an earthquake and that is the only correct interpretation, then he's wrong."
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