Cave-in likely not caused by earthquake, expert says

Justin Coons, Rocky Mountain News

Wednesday, August 8, 2007

The collapse of a Utah mine was most likely not caused by an earthquake, a U.S. Geological Survey spokesman said Tuesday.

Part of the Crandall Canyon Mine west of Huntington, Utah, collapsed early Monday, trapping six workers.

The University of Utah seismography station recorded seismic waves of 3.9 magnitude in the area at 2:48 a.m., with an epicenter about a mile below the Earth's surface, at the time of the collapse.

Experts initially said a quake triggered the cave-in, but now favor the theory that the force of the collapse caused the seismic waves.

"The signals don't look like what we usually see in a natural earthquake," said Harley Benz, spokesman for the USGS Geologic Hazards Team, based in Golden. "Those alone are more characteristic of a collapse."

The seismograph registered just one event Monday. If the 3.9 magnitude disturbance that was recorded came from an earthquake, there was no separate event recorded to signal the collapse of the mine.

"It depends on how far away the earthquake was from the mine," Benz said, adding that if the collapse and a quake happened at the same time and very close to one another, they could have registered as a single event.

Robert E. Murray, chairman of Murray Energy Corp., part owner of the mine, insisted his miners did not cause the collapse.

"This was caused by an earthquake, not something Murray Energy, not something Utah America Energy Inc., did," Murray said. "It was a natural disaster. It was an earthquake."

Earthquakes are common along the stretch of central Utah. The area has had numerous seismic events since 1990, with most registering at near-surface levels, at Richter magnitudes between 3.5 and 4.2.

Benz said many of the events were caused by mining.

"When you remove earth underground, you change the stress pattern in and around the (mine) shafts," he said. "By changing the strain patterns, you cause earthquakes.

"It's primarily due to distress in the material around the area. That will trigger earthquakes that wouldn't be natural."

Utah has an active natural seismic history. In 1988, a magnitude 5.2 earthquake occurred about 25 miles from Huntington.

Although they are leaning toward the theory that the waves recorded came from the collapse of the mine, experts will work to determine exactly what happened in the coming days.

Developments

• Seismic activity "totally shut down" efforts to reach six miners trapped two days below ground and wiped out all the work done in the second day of rescue efforts. "We are back to square one underground," Robert E. Murray, chairman of Murray Energy Corp., owner of the Crandall Canyon mine, said Tuesday evening.

• Rescuers remain unable to say whether the men are dead or alive, and had not heard any pounding from their hammers, as miners are trained to do when they get trapped.

• There were 30 pieces of heavy mining equipment in place and 134 people dedicated to the rescue, Murray said. Two C-130 aircraft from the Air Reserve in Pittsburgh were being sent with seismic equipment. Murray said the seismic equipment would be set up to detect signs of life. "We should know within 48 to 72 hours the status of those trapped miners."

• The trapped miners were believed to be about 3 1/2 miles inside the mine.

• Little was known about the six miners; only one has been identified. The Mexican Consulate in Salt Lake City said three of the men are Mexican citizens.

• Some of the miners' families may be illegal immigrants. Barbara Stinson Lee, spokeswoman for the diocese of Salt Lake City, asked photographers not to take pictures of families attending a Mass Tuesday night. "It is a request from the families that there be no photographs. It's not grief. It's an immigration issue. They don't need pictures on the front page of newspapers," Lee said.

coonsj@RockyMountainNews.com or 303-954-5617