Anomalous Propagation of Elastic Energy within the Moon

Abstract

THE records of the seismographs left on the lunar surface by the Apollo 11 and Apollo 12 missions have been discussed by Latham et al.¹. From the behaviour immediately following impact of the Apollo 12 ascent stage and similar events present on the records before and after, they have inferred that energy propagation as elastic waves over large distances can be represented as a diffusive process in a low loss elastic continuum. They calculate a diffusion coefficient of ∼ 1 km² s⁻¹ and a specific dissipation function Q ∼ 3,600 at a frequency of 1 Hz. If we use the time delay between the Apollo 12 impact and the commencement of the signal as the propagation time of an unscattered wave, we deduce a wave velocity of ∼ 3 km s⁻¹ and a scattering length ∼ 0.5 km. They emphasize that such a medium is quite unknown on Earth.