The investigation of the August 6, 2007 seismic event in Utah, which measured 3.9 in magnitude, has been submitted to the US Mine Safety and Health Administration as well as the Seismic Research Letters journal. In the 53-page report, the seismologists said the epicentre of the cave-in was near where the miners were working.

At 3018ft from east to west, from mine crosscut 143 to 120, and 722ft from north to south, the collapse measures an area about four times larger than originally estimated just after the events at Crandall Canyon.

“During the collapse, the space between the mine's roof and floor decreased by an average of only one foot, but enough coal and rock exploded from the mine's walls to fill much of the collapse area with rubble that likely prevented further collapse," the university experts said in their report, adding that the event occurred in a matter of seconds and would have left no time for the group to escape.

“The collapse probably happened within just a few seconds and was not a long, drawn-out affair," said one of the experts, geology associate professor Jim Pechmann.

“There would have been no time for anybody to get out of the way. It would have happened too fast for that."

Another new revelation by the seismologists at the U was that the initial collapse was followed by 37 aftershocks that were of measurable magnitude, primarily in the east and inferred west regions of the mine's collapse. They were likely a result of post-collapse stress, the report said, as well as from a vertical crack on the rock's west side.

Pechmann noted the revised location of the collapse's epicentre was thanks to new techniques whereby data from five seismometers above and near the mine were calibrated and paired with information on the known location of the August 16 "burst" of a 1.6 magnitude that killed three rescue workers and hurt six others.

UUSS director and seismologist Walter Arabasz said the difference in epicentre location now versus then was due in part to the location of the nearest seismic station, which was 12 miles away at the time of the collapse.

“That led some to conclude the seismic event was separate from the mine collapse," he said.

Evidence at the time also indicated that the seismic event – which measured at 3.9 that day – was indeed the collapse itself, not a natural quake that caused the mine's collapse, as argued by the mine's owner Murray Energy.

The new data on the epicentre show that it was within the complex's boundary and provide "strong evidence" that the quake and the collapse were one and the same.

“As seismologists, we're as certain as we can be that the seismic event registered as a magnitude-3.9 shock was due to the collapse of the mine and not a naturally occurring earthquake," Arabasz said.

The report also looked at the seismic history of the Wasatch Plateau-Book Cliffs coal mining region in Utah where the mine is located.

More than 17,000 seismic events between 1978 and August 2007 were attributed to underground mining, though most measured weaker than a magnitude 3. Less than 2% of events were organic in origination.

From the first of 2007 through the collapse in August of last year and looking in a 1.9 circumference, 28 detectable events were located, the group said. Eight of those happened within two-and-a-half weeks of the collapse’s commencement (all were a magnitude 1.9 or weaker) while 15 occurred in late February and early March (all 1.8 or less).

“These events occurred primarily in areas where there was concurrent or recent mining activity," the report states.

One bounce in March 2007, it added, forced crews to abandon the mine's north side due to the mine's damage and shift to the south side, where pillars were thicker. The latter region is where the six were located on August 6 when the mine tragedy occurred.

“We didn't see any indication of accelerating seismic activity in the hours before the collapse," said Pechmann. "We specifically looked for that."

He said later aftershocks were probably "continued failures of pillars supporting the roof due to stresses induced by the original collapse".

“And some aftershocks may have been due to adjustments within the roof," he added.

Pechmann and Arabasz studied the events with UUSS seismologists Kris Pankow and Relu Burlacu, as well as with University of Utah mining engineering professor Michael K McCarter.

The study was funded by the State of Utah and the US Geological Survey. The full report can be viewed at http://www.seis.utah.edu/