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• 14.0 POTENTIAL IMPACTS FROM LOCAL SEISMIC ACTIVITY <br />Earth tremors have been recorded or felt by local residents in the Somerset area since the early <br />1960s. The tremors commonly are the result of coalmine bumps and rock bursts, which are <br />spontaneous releases of strain energy in highly stressed coal and rock. In the Somerset Mine area <br />before closure, the bumps and rock bursts were common in room-and-pillar mining areas where <br />stresses concentrated within isolated pillars and blocks of coal (called bump blocks). Earth tremors <br />have continued sporadically in the Somerset Mine area since the mine was closed in the 1980s. <br />Tremors generated by bumps and rock bursts in the Somerset Mine area attain magnitudes that <br />have shaken structures in the West Elk Mine area and have been felt sometimes by West Elk Mine <br />personnel. These local tremors may affect, to a minor degree, underground workings, landslide or <br />potential rockfall areas, particularly during prolonged periods of increased precipitation. It is <br />noteworthy, however, that the Rulison nuclear shot in 1969, which produced a tremor with a Richter <br />magnitude of 5.2 (the magnitude of energy released was many times greater than the magnitudes <br />of any recorded bump or rock burst), did not affect the Somerset Mine. To our knowledge the <br />Rulison nuclear shot did not trigger any landslides or rockfalls, nor did it impact reservoirs, ponds, <br />or streams in the South of Divide or Dry Fork mining areas. <br />LJ <br />• <br />Terra Tech - 0907171P 32