Strong Heterogeneity in Shallow Lunar Subsurface Detected by Apollo Seismic Data

Experiencing heavy impacting, the Moon preserves a megaregolith in its shallow subsurface with physical properties that carry implications for lunar history. A strong scattering of seismic waves associated with the heterogeneous lunar megaregolith appears to be systematic, but deriving a statistical law of the random heterogeneities has remained elusive. Apollo seismic data are characterized by ultra-long coda waves with weak amplitude decay that provide an opportunity to explore the extent of heterogeneity in the lunar crust. We obtain by numerical simulation the appropriate parameters for seismic velocity and density perturbation of the shallow lunar crust that match Apollo seismic data. The perturbations of the shallow lunar crust identified here, which are at least 50%, are much larger than previously thought. This physical behavior thus both confirms a strongly heterogeneous surface layer as well as provides a new constraint on the structural characteristics of the megaregolith.