Fatal mine collapse covered 50 acres

Seismology report: disaster began near where miners worked

This map shows the part of the Crandall Canyon Mine that was being mined in August 2007, when a collapse occurred. A smaller collapse in March 2007 (red rectangle marked... Click here for more information.

SALT LAKE CITY– New calculations show that the deadly Crandall Canyon mine collapse – which registered as a magnitude-3.9 earthquake – began near where miners were excavating coal and quickly grew to a 50-acre cave-in, University of Utah seismologists say in a report on the tragedy.

The University of Utah Seismograph Stations estimated the size of the collapse is about four times larger than was thought shortly after the time of the Aug. 6, 2007, disaster that resulted in the deaths of six miners and, 10 days later, three rescuers.

The seismologists' 53-page report has been submitted to the journal Seismological Research Letters and to federal Mine Safety and Health Administration (MSHA) investigators. Among the key findings:

• Seismological and other data suggest the size of the area that collapsed in the nearly horizontal mine measured 920 meters (3,018 feet) from east to west – extending from about mine crosscut 143 to crosscut 120 – and measured 220 meters (722 feet) from north to south – a total of 50 acres. A crosscut is a north-south tunnel in this mine.
  
  

• During the collapse, the space between the mine's roof and floor decreased by an average of only 1 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 collapse likely lasted only seconds – leaving no time for escape – and not for misery-prolonging minutes as some miners' families have feared. The misconception arose from the fact seismic waves reverberate for much longer than the collapse or earthquake that generated them.
  
  

• The mine collapse was followed in August by 37 measurable aftershocks, clustered near the east and inferred west ends of the collapse area, probably from post-collapse stress and from a vertical crack on the west end of the collapsed block of rock.
  
  

• Seismologists recalculated the epicenter of the magnitude-3.9 mine collapse, and found it "was within the mine boundary and very close to where the miners were working," says the study's lead author, seismologist Jim Pechmann, a research associate professor of geology and geophysics at the University of Utah Seismograph Stations.