Overview of Mining-Induced Seismicity in UtahAugust 15, 2007 |
Mining-Related Seismicity in the
WP-BC Coal Mining Region
Jan. 1978 – Aug. 2007
Figure. Epicenter map of all seismic events (N = 19,122) located by the University of Utah regional seismic network in the Wasatch Plateau–Book Cliffs coal mining region from January 1, 1978, through August 9, 2007. Polygons (after Arabasz et. al., 1997) circumscribe areas within which nearly all seismicity is inferred to be mining-related. Stars indicate mining-related seismic events with M>3.5 in this area. Quaternary faults are shown by light lines. Modified from Arabasz and Pechmann (2001).
Overview of Mining-Induced Seismicity in Utah
(text adapted from: Arabasz, W.J., R. Burlacu, and K.L. Pankow, 2007, An overview of historical and contemporary seismicity in central Utah, in Willis, G.C., Hylland, M.D., Clark, D.L., and Chidsey, T.C., Jr., editors, Central Utah—diverse geology of a dynamic landscape: Utah Geological Association Publication 36,in press)
Seismicity caused by underground mining in the arcuate crescent of the Wasatch Plateau and Book Cliffs coalfields in east-central Utah (polygons, on above figure) is a well-recognized phenomenon that has been studied since the 1960s (see reviews and case studies by Wong, 1993; Arabasz and others, 1997, 2005; Arabasz and Pechmann, 2001; Ellenberger and others, 2001). Annual coal production from these fields currently exceeds 25 million short tons, with longwall mining (at depths less than 960 m) accounting for the majority of the production (Vanden Berg, 2006). Following Arabasz and others (2005), we use the terms mining seismicity, mine tremors, and mining-induced seismicity (MIS) interchangeably, each encompassing all seismic events caused by mining. Most of the MIS is smaller than M 3, and probably all the MIS is at or very close to mine level (e.g., Ellenberger and others, 2001; Arabasz and others, 2005). Arabasz and Pechmann (2001) summarized information for 17 mine tremors of 3.0 <ML< 4.2 in the Wasatch Plateau-Book Cliffs region between 1978 and June 2000. Two of the largest were shocks of M 3.8 in February 1998 and M 4.2 in March 2000; both had shear-slip focal mechanisms and occurred in the rock mass adjacent to workings in the Willow Creek mine. The remaining mine tremors were shown or inferred to be caused by sudden roof-floor closure (see also Fletcher and McGarr, 2005), either associated with pillar runs in older room-and-pillar mine workings, or with pillar failure in entryways adjacent to longwall workings.
Do the polygons on the above figure contain tectonic earthquakes as well as MIS? Arabasz and Pechmann (2001) found at least one tectonic earthquake in their study of earthquakes of ML> 3.0 in the Wasatch Plateau-Book Cliffs mining region—an earthquake of ML 3.0 with a well-constrained depth of 11 km and a normal-faulting focal mechanism. In systematic attempts to discriminate tectonic earthquakes within the MIS polygons, we have typically found a small number of candidate events (< 2% of the catalog sample) that arguably might represent tectonic earthquakes, based on source-mechanism and (or) focal-depth information (e.g., Arabasz and Pechmann, 2001, p. 3-5; Arabasz and others, 2005).
References
Arabasz, W.J., Nava, S.J., McCarter, M.K., Pankow, K.L., Pechmann, J.C., Ake, J., and McGarr, A.M., 2005, Coal-mining seismicity and ground-shaking hazard—A case study in the Trail Mountain area, Emery County, Utah: Bulletin of the Seismological Society of America, v. 95, p. 18–30, doi: 10.1785/0120040045.
Arabasz, W.J., Nava, S.J., and Phelps, W.T., 1997, Mining seismicity in the Wasatch Plateau and Book Cliffs coal mining districts, Utah, USA, in Gibowicz, S.J., and Lasocki, S., editors, Rockbursts and seismicity in mines, Proceedings of the 4th International Symposium on Rockbursts and Seismicity in Mines, Krakow, Poland: Rotterdam, A. A. Balkema, p. 111–116.
Arabasz, W.J., and Pechmann, J.C., 2001, Seismic characterization of coal-mining seismicity in Utah for CTBT monitoring: report to Lawrence Livermore National Laboratory, LLNL Research Agreement No. B344836, variously paginated, 3 appendices. Online, http://www.seis.utah.edu/Reports/llnl2001/index.shtml, accessed August 2007.
Ellenberger, J.L., Heasley, K.A., Swanson, P.L., and Mercier, J., 2001, Three dimensional microseismic monitoring of a Utah longwall, in Elsworth, D., Tinucci, J.P., and Heasley, K.A., editors, Rock Mechanics in the National Interest: Rotterdam, A. A. Balkema, p. 1321–1326.
Fletcher, J.B., and McGarr, A., 2005, Moment tensor inversion of ground motion from mining-induced earthquakes, Trail Mountain, Utah: Bulletin of the Seismological Society of America, v. 95, p. 48–57, doi: 10.1785/0120040047.
Vanden Berg, M.D., 2006, Annual review and forecast of Utah coal—Production and distribution, 2005: Utah Geological Survey Open-File Report 481, 32 p. Online, http://www.geology.utah.gov/online/ofr/ofr-481.pdf, accessed August 2007.
Wong, I.G., 1993, Tectonic stresses in mine seismicity—Are they significant?, in Youngs, R.P., editor, Rockbursts and seismicity in mines 93: Proceedings of the 3rd International Symposium on Rockbursts and Seismicity in Mines, Ontario, Canada: Rotterdam, A. A. Balkema, p. 273–278.