- © 2008 by the Seismological Society of America
On 6 August 2007 a local magnitude 3.9 seismic event occurred at 08:48:40 UTC in central Utah. The epicenter is within the boundaries of the Crandall Canyon coal mine (cf. Pechmann et al. 2008, this issue of SRL). We performed a moment tensor analysis with complete, three-component seismic recordings from stations operated by the U.S. Geological Survey (USGS), the University of Utah, and EarthScope. The analysis method inverts the seismic records to retrieve the full seismic moment tensor, which allows for interpretation of both shearing (e.g., earthquakes) and volume-changing (e.g., explosions and collapses) seismic events. The results show that most of the recorded seismic wave energy is consistent with an underground collapse in the mine. We contrast the waveforms and moment tensor results of the Crandall Canyon Mine seismic event to a similarsized tectonic earthquake about 200 km away near Tremonton, Utah, that occurred on 1 September 2007. Our study does not address the actual cause of the mine collapse.
We apply the moment tensor analysis techniques described in Ford et al. (2007) to improve our understanding of the source of the seismic waves for two very different recent events in Utah. Ford et al. (2007) implement the time-domain full regional waveform inversion for the complete moment tensor (2nd rank tensor, Mij) devised by Minson and Dreger (2008) after Herrmann and Hutchensen (1993) based on the work of Langston (1981). Moment tensors are determined by matching synthetic seismograms to data at periods where the Earth can be characterized by a simple plane layer model. The complete moment tensor allows for a characterization of the relative amounts of deviatoric and isotropic (Mij where i=j) source components and a constraint on the source depth. The isotropic component is related to the volume change associated …