2009-05-01_REPORT - C1980007 (2)

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INTRODUCTION This report is prepared by David Butler, Senior Geophysicist, Zonge Geosciences, Inc., Lakewood, Colorado, in partial fulfillment of a commitment by Mountain Coal Company (MCC) to monitor seismicity (including the microseismic activity near longwall mining activity) in the North Fork Valley just east of Paonia, Colorado. This commitment is to the Colorado Division of Natural Resources, Division of Reclamation, Mining and Safety. The area encompassed extends east-west from Coal Creek Mesa to West Tower Mountain and north-south from Terror Creek Reservoir to Lion Mesa (see Figure 1). The area includes West Elk Mine operated by Mountain Coal Company, LLC and Bowie No. 2 Mine, property of Bowie Resources, LLC (BRL). Seismicity from Elk Creek Mine owned by Oxbow Mining, Inc. is also recorded. This report contains preliminary analyses of data collected in the second quarter of 2007, i.e. from April to June, 2007. Stations in the network operated previous to this quarter, but this report contains only information about the second quarter of 2006. Some seismological aspects of the analysis are not yet completed. The velocity model, a ground-motion attenuation model, station delay times and network magnitude definitions are under construction. Further development of these parameters and models will lead to refinement in the calculated event location coordinates and magnitude estimations; however, the basic record of the seismic activity will remain unchanged. This report focuses on progress towards seismologic conclusions completed during the analysis period. The seismic monitoring program was designed to monitor seismicity levels, provide locations for local events, measure ground motion quantitatively, determine focal mechanisms when feasible, and establish the ground motion regime that structures within the network are and will be subject to during mining. OPERATIONS Station Locations and Descriptions A multi-station seismic array (10 stations) was installed by a cooperative effort of MCC and BRL and the Spokane Research Laboratory of NIOSH/CDC (National Institute for Occupational Safety and Health/Centers for Disease Control and Prevention). Station locations were determined by consideration of access, permission of landowners, specific array geometry, radio line-of-sight to the common recording site (the Paonia Airport) or a repeater station and uniform coverage of the target area (see Figure 1). The location of stations presently operating are shown on Figure 1 and corresponding station coordinates are listed in Table 1. The delay times shown are discussed below.