Thermally induced changes of the seismic velocity in the lunar regolith

Abstract: The Apollo 17 mission installed seismic equipment on the lunar surface that was in continuous operation during eight month in 1976 and 1977. Applying Passive Image Interferometry we use this data set to infer weak periodic changes of the S-wave velocity in the lunar soil. The principles of this technique are outlined and its success in monitoring velocity changes is demonstrated by means of terrestrial examples. It is shown that the lunar data is suitable for this approach too. Direct Rayleigh waves as well as scattered coda waves can be retrieved by correlation of ambient vibrations recorded at different lunar geophones. Variations of the seismic velocity are continuously measured for the eight month period of available data. According to spectral analysis the variations are linked to the Sun-synodic period of 29.5 days which suggests that these variations are caused by temperature changes due to variable illumination from the sun. Numerical modeling of the temperature diffusion in the lunar subsurface agrees well with the observation and can be used to refine our models of the thermal properties of the shallow lunar crust. ------------------------------------------------------------------------ Séminaires de l'équipe de géophysique spatiale et planétaire ------------------------------------------------------------------------