Figure A

Preliminary plot of magnitude versus time (UTC) for 152 seismic events in the University of Utah earthquake catalog located within 3.0 km (1.9 miles) of the inferred location of the collapse in the Crandall Canyon mine and preceding the August 6, 2007, shock. The plotted data are for the period beginning on August 1, 2005, and ending on August 6, 2007, at the time of the main seismic event. Focal-depth resolution for most of the events is poor. Further study will be required to test whether any tectonic earthquakes below mine level are included in the sample. Experience elsewhere suggests that most, if not all, of the events are probably shallow and mining-related.