Numerical study of seismic scattering and waveguide excitation in faulted coal seams

The definitive version is available at www.blackwell-synergy.comFinite-difference P-SV simulations of seismic scattering characteristics of faulted coal-seam models have been undertaken for near-surface P- and S-wave sources in an attempt to understand the efficiency of body-wave to channel-wave mode conversion and how it depends on the elastic parameters of the structure. The synthetic seismograms clearly show the groups of channel waves generated at the fault: one by the downgoing P-wave and the other by the downgoing S-wave. These modes travel horizontally in the seam at velocities less than the S-wavespeed of the rock. A strong Airy phase is generated for the fundamental mode. The velocity contrast between the coal and the host rock is a more important parameter than the density contrast in controlling the amplitude of the channel waves. The optimal coupling from body-wave energy to channel-wave energy occurs at a velocity contrast of 1.5. Strong guided waves are produced by the incident S-sources for source angles of 75° to 90° (close to the near-side face of the fault). As the fault throw increases, the amplitude of the channel wave also increases. The presence of a lower-velocity clay layer within the coal-seam sequence affects the waveguiding characteristics. The displacement amplitude distribution is shifted more towards the lower-wavespeed layer. The presence of a ‘washout’ zone or a brecciated zone surrounding the fault also results in greater forward scattering and channel-wave capture by the coal seam.S.A. Greenhalgh, B. Zhou, D.R. Pant and A. Gree