Apollo 12 Seismic Signal: Indication of a Deep Layer of Powder

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Science  11 Sep 1970:
Vol. 169, Issue 3950, pp. 1071-1075
DOI: 10.1126/science.169.3950.1071


The seismic signal caused by the Apollo 12 lunar module is interpreted in terms of propagation between source and receiver through a layer of powder in which sound velocity increases with depth. This increase, which is due to compaction, extends over several kilometers and leads to a concentration of seismic waves toward the surface. Computer simulations with the use of ray acoustics and on the assumption of a randomly undulating lunar surface approximate well the observed signal. Seismic amplitudes are greatly enhanced in such a medium compared to solid rock, so that the observed signal requires less power to be transmitted than previously estimated.