Crandall Canyon Mine in EOS
I recently renewed my subscription to EOS, the weekly newsletter of the American Geophysical Union. An article on the Crandall Canyon Mine collapse appeared in the issue published back on August 21st. Staff writer Randy Showstack reports the consensus view among seismologists, which I previously summarized here in this blog, that the 3.9 magnitude event was probably caused by an underground cavity collapse rather than a tectonic earthquake.
Showstack interviewed a number of geophysicists, including Douglas Dreger of the Berkeley Seismological Laboratory (BSL) at the University of California, Berkeley. Dreger emphasized that the pattern of "first motions" shown in the seismographs is not the alternating pattern that would indicate an earthquake. Instead, Dreger said, the ground moved down initially. James Pechman, research associate professor of geology and geophysics at the University of Utah, also argues for an underground collapse due to the fact that “all the P wave first motions in the University of Utah network for this seismic event were downward or dilatational. That is not definitive by itself, but in these areas with lots of coal mine–induced seismicity, when we see all downward first motion, we expect a collapse event in the mine.”
Showstack concludes his piece by noting that Robert E. Murray, co-owner of the Crandall Canyon Mine, was continuing to attribute the mine collapse to a natural
earthquake. Murray's interpretation, as Showstack notes, is at variance with the consensus of geophysicists who have inspected the seismological records from the event.