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North Fora Valley Seismic Network — Fourth Quarter 2009
<br />have an ML assigned, we converted the MC (Table 3) assigned by the automatic location program
<br />to ML, using a relationship we developed for seismic events, which had both Mc and ML.
<br />As can be noted in Figure 3, the typical scatter seen in ground motion data is exhibited by the
<br />NFVSN data. The McGarr and Fletcher (2005) curves lie above the central tendency of the data
<br />and in particular, the curves are very conservative at distances less than 1 km. We are currently
<br />developing a model to fit the North Fork Valley data.
<br />BRL has adopted a "threshold" event where the associated PGA value is 0.05 g or higher as
<br />recorded at station TCR adjacent to Bruce Park Dam. No damage is expected at this level of
<br />ground motion but inspection of the dam and analysis of the event will be performed. Ground
<br />motions (including time histories) with average maximum accelerations of over 0.16 g (GEI
<br />Consultants, 2002) were used to evaluate the Bruce Park Dam. The dam was judged to be safe
<br />under that input of seismic loading.
<br />ACKNOWLEDGMENTS
<br />The NFVSN data analysis and evaluation are jointly supported by MCC and BRL. Our thanks to
<br />Jim Abshire, BRL Project Manager and Wendell Koontz, MCC Project Manager for their
<br />support. Our appreciation to Pete Swanson (NIOSH /CDS) and Dave Wolny (Mesa State
<br />College) for their assistance in the operation and maintenance of the network. Our thanks to
<br />Melinda Lee for her assistance in the preparation of this report.
<br />REFERENCES
<br />Banfill, R., 1995, PC -SUDS Utilities, A collection of tools for routine processing of seismic data
<br />stored in the seismic unified data system for DOS (PC- SUDS).
<br />GEI Consultants, Inc., 2002, Geotechnical evaluation of mine - induced seismicity on Bruce Park
<br />Dam, Delta County, Colorado: unpublished report submitted to Bowie Resources,
<br />Limited.
<br />Johnson, C.E., Bittenbinder, A., Bogaert B., Dietz L., and Kohler W., 1995, EW: A Flexible
<br />Approach to Seismic Network Processing: IRIS Newsletter, v. 14, no. 2, p. 1 -4.
<br />Koontz, W., 2007, Memorandum on the West Elk Mine B Seam Bounce on November 17, 2007,
<br />2 p.
<br />McGarr, A. and J.B. Fletcher, 2005, Development of Ground- Motion Prediction Equations
<br />Relevant to Shallow Mining- Induced Seismicity in the Train Mountain Area, Emery
<br />County, Utah, Bulletin of the Seismological Society of America, v. 95, p 31 -47.
<br />Swanson, P., 2009, personal communication on status on OXM timing and telemetry problems.
<br />Swanson, P. and Koontz, W., 2006, Measurement and analysis of mining induced seismic
<br />ground motion in the vicinity of the West Elk Coal Mine, Somerset, CO (abstract):
<br />Seismological Research Letters, v. 77, no. 2, p. 318.
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