Bubble pulses and power spectra of some marine seismograms

Abstract

Marine seismograms from a marine refraction survey done in Lake Superior with "geogel" explosives are studied in terms of their spectral content in relation to various shot sizes (1.25-200 lbs). The effect of bubble pulse oscillations plays a dominant role in the analysis. A heuristic approach is used throughout and it is concluded that the use of small shots is advisable, whenever possible, in marine refraction surveys on account of the relatively broad advisable, whenever possible, in marine refraction surveys on account of the relatively broad spectra in comparison with those for larger shots. Also, if a deconvolution process is used to remove the bubble pulse effects from a seismogram having a narrow spectrum, nothing very meaningful would remain for interpretation. From observations of the bubble pulse periods, sizes of shots, and depths of detonation, the Rayleigh-Willis constant is determined for the Lake Superior environment. The calculated value of 5.0 yields bubble periods comparable to those observed. However this value differs from other values such as 4.19 obtained by Worzel and Ewing (1948) and 4.36 obtained by a group at Woods Hole Oceanographic Institute (Shor, 1963) using TNT explosives at sea. The constant seems dependent on both the type of explosive and the shooting environment.