According to analysis results of channel waves recorded in a 0.9m-thin coal seam when using blasting as seismic source, the result of energy spectrum shows two major frequency bands in those channel waves. One is centered at 2000 Hz, and the other is at 490 Hz. Furthermore, the two frequency bands are not continuous and the difference of peak values is not obvious between these two bands. It is apparent that these two frequency bands are triggered at the same time in the time frequency distribution graphics of channels wave, moreover, the distribution of wavelet coefficients in these two frequency bands is similar to some degree. This is totally different from channel waves that were recorded in a 2.1m-thick coal seam. The Airy phase frequency and speed observed in the testing field is about 550 Hz and 824.5 m/s, respectively, which are close to theoretical ones of Airy phase with 0.9m thickness. Because seismic boreholes were deployed in the middle of coal seam, the energy of dynamite would be distributed symmetrically on the face of coal seam. It would be very important for generating the symmetrical wave shape mode. Similarly, since the thickness of coal seam is only 0.9 meters, the energy of dynamite would be enough to vibrate the roof and floor by the seismic source. The vibration plays a key role for generating the second higher wave mode of channel wave. Therefore, the speed of channel wave is close to the speed of S wave in rocks, which is positive to identify the speed of S wave in rocks from channel waves recorded in thin coal seams. Furthermore, the analysis method of combining low with high frequency region would be recommended to reinforce the effectiveness of detecting by channel waves.
