A well-known difficulty in coal mining is the unexpected occurrence of minor faults, by which the seams are displaced by only one or a few meters. It is practically impossible to predict such faults from geophysical surveys on the surface of the earth. However, as coal normally has a very low velocity and, also, only a small density compared to the neighboring rocks, channel waves along the seams are theoretically possible as will be shown. Such channel waves have been successfully produced and recorded by underground seismic work within a German coal mine. Moreover, a reflection from a known minor fault could clearly be observed.

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