Microseismic Activity Associated with Longwall Coal Mining (c358bd13-dd66-47a2-868a-2f894415e1bb)

Field studies were conducted over a longwall coal mining operation to investigate the feasibility of using microseismic techniques to detect and to locate any areas of instability in the vicinity of the longwall. An array of geophones buried at depths of 3 to 8 m from surface were positioned approximately 130 m above the active area of the longwall panel. A mobile microseismic monitoring facility amplified, filtered, and recorded the microseismic activity sensed by the geophones. Microseismic events were detected at depths of at least 130 m and at horizontal distances in excess of 250 m from the source. Most events, which resembled decaying sinusoidal transients, had frequencies of 10 to 100 Hz, and particle velocities of 1 to 8 pm/s. Source locations for the 150 largest events were computed using a least-square travel-time-difference method. Both isotropic and unique wave propagation velocity models were considered when evaluating the source locations. Most of the events were computed to be within ± 30 m vertically of the coal seam and ± 15 m horizontally of the longwall face, when the unique velocity model was employed.