The latest geological investigation on last summer’s Crandall Canyon mine collapse concluded that the starting point of what seismometers recorded as magnitude-3.9 earthquake was in fact the place where miners were excavating coal, University of Utah specialists said.

The disaster occurred on August 6, 2007, when six miners and, 10 days later, three rescuers, were killed. The collapse area covered 50 acres, lasted for only a few seconds, and is most likely to have killed the miners inside instantly. The three rescuers died in a rescue attempt 10 days later in a subsequent collapse.

The 53-page report, which has already been sent to the journal Seismological Research Letters and to federal Mine Safety and Health Administration (MSHA), concluded that the mine collapse was not triggered by a seismic event, but was in fact the source that triggered what seismometers recorded as a seismic event.

The size of the area collapsed measured 920 meters (3,081 feet) from east to west, and 220 meters (722 feet) from north to south. Considering the space between the mine’s roof and tunnel measured only 1 foot, the rubble filling the collapse area prevented further collapse.

For the families of the miners, who believe the victims may have struggled to get out of the mine after the collapse, investigators said they stood no chance, and that they suffered a quick death, rather than spending agonizing minutes trying to escape.

According to seismological calculations, the epicenter of the magnitude-3.9 collapse was “within the mine boundary,” in the place where the miners were excavating. This goes against mine owner Bon Murray’s claims that an earthquake triggered the collapse.

By combining data from five seismometers, investigators concluded that the second collapse, which killed the three rescuers and injured six others on August 16, was also centered near the mine.

Seismologist Walter Arabasz, director of the University of Utah Seismograph Stations explained that the miscalculation of the preliminary epicenter soon after the collapse led to the assumption that there had been in fact two separated events, a seismic one and the mine collapse.

This was due to the fact that the nearest seismic station was 12 miles away, and the initial calculations placed the epicenter of the event 0.4 miles outside the boundaries of the mine, and 0.6 miles west-southwest of the real epicenter.

Seismologists concluded that there can be no doubt on the magnitude-3.9 event: it was not an earthquake, but the mine collapse that triggered it. The study was funded by the State of Utah and the U.S. Geological Survey.

Utah seismologists, together with seismologists from the University of California, Berkeley and Lawrence Livermore National laboratory, said that the vertical movement recorded during the collapse excludes the idea of an earthquake (which is triggered by shear motion along a fault).

By overlapping the patterns of the mine collapse and a natural earthquake, the seismic waves are very different, indicating that 20 percent of the energy released during the collapse came from vertical shearing motion, which excludes the possibility of an earthquake.

Furthermore, the seismic records indicate that the vertical shearing motion started prior to the collapse. “It cannot be interpreted as an earthquake that triggered the collapse,” seismologist Jim Pechmann, research associate professor of geology and geophysics at the University of Utah Seismograph Stations said.

Utah’s coal mining region is well-known for the large number of seismic events that have occurred in the past three decades (over 17,000), only 2 percent of which were natural earthquakes.

The complete seismological report on the August 6, 2007 Crandall Canyon mine collapse is available at http://www.seis.utah.edu/.