The Moon's Crust and Upper Mantle Discontinuities Revealed by Seismic Interferometry Methods Applied to Apollo Seismic Data

Abstract Seismic determination of the Moon's crustal thickness is crucial for understanding its formation, composition, and evolution. Additionally, crustal thicknesses below seismic stations serve as anchoring points for 3D crustal thickness maps derived from gravity and topography field variations. However, strong seismic scattering inside the Moon can prevent seismic waves reflected on, or converted at, crust and upper mantle discontinuities from reaching the surface without interacting with scatterers. This study estimates Auto‐Correlation Functions (ACF) of all channels of Apollo seismometers during the coda of high‐signal‐to‐noise seismic events. As expected for a strongly scattering medium, Apollo stations S12 and S15 do not detect late arrivals in the ACF indicative of waves reflected on internal discontinuities. However, station S16 and, to a lesser extent, station S14 show stable late arrivals in the ACF. Arrivals at 14.2 and 27.1 s and at 23.9 and 50.6 s in the ACF of vertical and horizontal mid‐period channels of station S16 are interpreted as and waves reflected at mid‐crustal and crust‐mantle interfaces. A seismic crust and upper mantle model beneath station S16 fits the arrival times of and waves with realistic seismic velocities and ratios ranging from 1.65 to 1.88. The crustal thickness is non‐uniquely estimated at 53 km below station S16. Our results are also compatible with significant variations in the properties of the interfaces, or in strength of seismic scattering between Apollo stations.