Summary of results of seismic surveys. Coal seams can be clearly identified on well logs from wells Hon 3 and Hon 9. Each vertical band is for a range of frequencies that increases to the right; i.e., low frequency band on the left (10-50 Hz) and high frequency band (100-1200 Hz) on the right. The upper part of the figure exhibits the seismic response of individual seams before velocity reduction, and the lower part shows the response after 20% velocity reduction. Note that changes in the seismic response resulting from injection of carbon dioxide or evolution of coalbed methane can only be observed at frequencies in the 100-800 Hz and 100-1200 Hz bandwidths (area within the blue rectangles).