2008-01-30_REPORT - C1980007 - Laserfiche WebLink

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:?sr_c _:rrr _•-.=-.-<rr:r .'.?-r___r_-f_.._._...._....._....rr.c?-.u:r^r_r:-?;;trr---.r.':..r r....,<,•.?, - _: err _ ..y?rr r""P.-•:r-?:<5":=r--`: i•--; '??=-•>x'r'r-;.:.r<.<_. ,.? 'gE? <rrf rr :=f J::?Yi::-=-?i: ?'m`?`. -•?,??=-?rd:, -..•:..,., :.. ;._: .. .?i ?_r_, ?r.rrr. ?s.r..x:vrs??.-_-_ T`?" __r__.r.r....,..rar_ar_r_..rr.r.-.:<e??i.-...,5?„?srr:.}?r...-r<!•..1.??`.'?'?._...i?1 .. ............. .. .:... y.. .':? .-.?:-..-___________.__._y:-..__......o ?'?#:....?____.? North Fork Valley Seismic Network - Third Quarter 2007 SUMMARY During the three-month period, 1 July to 30 September 2007, 187 mining-related seismic events were relocated with approximate Richter local magnitudes (ML) 1.5 and larger using data recorded on the North Fork Seismic Network. Most of the events were located in four clusters: two at the Bowie No. 2 Mine, one at the Elk Creek Mine, and one at the West Elk Mine, indicating the areas being worked at each of these mines. About one-third of the seismic events (61) occurred at the West Elk Mine. The two largest events, both ML 2.6, were located at or close to the West Elk Mine and occurred on 9 and 15 August, respectively. The highest peak horizontal ground acceleration (PGA) recorded during the third quarter was 0.09 g at station FGH in the Bowie Mine area which resulted from a ML 1.9 event at a distance of about 0.7 km [0.4 mil. The largest PGA recorded at the West Elk Mine was 0.005 g at station WFW resulting from a ML 2.6 event that occurred on 9 August at a distance of 2.4 kin [1.5 mi]. INTRODUCTION This report has been prepared in partial fulfillment of a commitment by Mountain Coal Company (MCC) to monitor seismicity (including the microseismic activity near the 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. This report contains preliminary analyses of the data collected for the third quarter of 2007 (1 July through 30 September). The area included in this study encompasses the 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 on the North Fork Network. The 10-station North Fork Valley Seismic Network (NFVSN) was established to monitor the mining-related seismicity occurring in the vicinity of the West Elk and Bowie No. 2 mines at a detection threshold magnitude of ML 1.0, provide event locations and magnitudes and estimates of ground motions, and determine focal mechanisms when feasible. NETWORK OPERATIONS The NFVSN consists of 10 permanent stations, which were installed as a cooperative effort between MCC, BR.L and the Spokane Research Laboratory of the National Institute of Occupational Safety and Health/Centers for Disease Control and Prevention (NIOSH/CDC). The following factors were used to determine the station locations: access, permission of land owners, network geometry, radio line-of-sight to the common recording site at Paonia airport or a repeater station; and uniform coverage of the target area (Figure 1). Each station consists of three-component accelerometers. The locations of seismographic stations operating during the 2007 third quarter are presented in Table 1 and shown on Figure 1. je W:1X_WLFSIPROJECTStWEST ELK-M7N COAL12007 0=3_2007_MCC_FINAL.D0( f29 JAN-08V10AK 1 i I