Seismic activity has shut down efforts to reach six miners trapped below ground and has wiped out all the work done in the past day, said Robert E. Murray, chairman of Murray Energy Corp., owner of the Crandall Canyon mine.

“We are back to square one underground,” Murray said. He added that “we should know within 48 to 72 hours the status of those trapped miners.”

“There is absolutely no way that through our underground rescue effort we can reach the vicinity of the trapped miners for at least one week,” Murray said.

Rescue crews are drilling two holes into the mountain in an effort to communicate with the miners, assuming they are still alive, the Associated Press reports.

Meanwhile, unstable conditions below ground have thwarted rescuers’ efforts to break through to the miners, who have been trapped 1,500 feet below the surface since Monday, Murray said.

The National Earthquake Information Center in Colorado said ten seismic shocks have been recorded since the collapse, but only one since 3 a.m. Tuesday, according to AP. That one struck at 3:42 p.m. with a magnitude of 1.7.

Murray has insisted the cave-in was caused by an earthquake. But government seismologists have said the pattern of ground-shaking picked up by their instruments around the time of the accident Monday appeared to have been caused not by an earthquake, but by the cave-in itself.

Murray lashed out at the news media for suggesting his men were conducting “retreat mining,” a method in which miners pull down the last standing pillars of coal 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 angrily. “It was a natural disaster. An earthquake. And I’m going to prove it to you.”

Amy Louviere, a spokeswoman for the federal Mine Safety and Health Administration, said the men at the mine were, in fact, conducting retreat mining.

However, Louviere said that exactly what the miners were doing, and whether that led to the collapse, can be answered only after a full investigation.

Retreat mining has been blamed for 13 deaths since 2000, and the government requires mining companies to submit a roof control plan before beginning such mining. Such a plan details how and when the pillars will be cut and in what order.

The Crandall Canyon mine had submitted such a plan and received approval in 2006, Louviere said.

“As long as they abide by that plan, it can be a very safe form of mining,” she said. “What we’ve found with recent fatalities that the operator was found to not be following the roof control plan.”