A Colorado expert said Wednesday that the decision to stop digging toward six trapped Utah miners because of ongoing underground disturbances makes sense.

"Since the original collapse, there have been a number of small, you could call them aftershocks," said John Bellini, a geophysicist at the National Information Center in Golden. "After you have a large (mine) collapse like that, the ground is going to be settling or there's some stress changes in the area."

Dangerous seismic conditions that have set back efforts to reach the miners could prevent crews from reaching the men for at least a week, said Bob Murray, chairman of Murray Energy Corp., part owner of the mine.

There's an ongoing debate, however, over whether a quake caused the early Monday mine collapse as Murray has insisted.

He also lashed out at news media for suggesting his men were conducting "retreat mining," in which miners pull down the last standing pillars of coal after mining out an area and let the roof fall in.

"This was caused by an earthquake, not something that Murray Energy . . . did or our employees did or our management did," he said.

"It was a natural disaster, an earthquake. And I'm going to prove it to you."

Bellini, however, said preliminary analysis indicates the 3.9 magnitude temblor recorded early Monday at the time of the shaft collapse was the cave-in, not an earthquake.

"The wave forms between an earthquake and a mine collapse have different characteristics," he said. "This event did not have the characteristics of a typical, natural occurring earthquake."

Amy Louviere, a federal Mine Safety and Health Administration, said retreat mining was going on at the mine in a remote canyon 140 miles south of Salt Lake City.

She said that exactly what the miners were doing at the time of the collapse, and whether that led to the tragedy, can be answered only by a full investigation.

gathrighta@RockyMountainNews.com or 303-954-5486 The Associated Press contributed to this report.