SYNTHETIC SEISMOGRAMS APPLIED TO THE SEISMIC INVESTIGATION OF A COAL BASIN*

In the present study an attempt is made to relate the general pattern of reflection seismograms obtained over a coal basin to the acoustical properties peculiar to the Coal Measures. The Carboniferous is characterized by a very rapid succession of distinct lithological units, resulting in a surprising variability in their physical properties. Coal seams in particular are conspicuous by their low density and velocity and they produce acoustical contrasts of 35–50 % with respect to country rock. The resulting heavy shielding action prevents the seismic energy from penetrating deeply into this type of formation.

With the aid of synthetic seismograms, arranged into synthetic profiles, it is shown that only a minor part of the Coal Measures reflections is of primary origin. The majority has a secondary character brought about by reverberations inside the weathering zone. Thus the conclusion is reached that reflection shooting allows of mapping only the structure of the top section of the Carboniferous, which is sufficient for the purposes of the coalmining industry.