 Apollo lunar seismology

Apollo lunar seismology uses ground-motion recordings from instruments placed on the Moon during the Apollo missions. Natural moonquakes and impacts provide sources whose waves sample the lunar interior. The station positions, source locations and seismic velocity model jointly determine the paths expected for each arrival.

Weak deep-interior phases are difficult to identify amid long scattered wave trains. Combining records from repeated deep moonquakes and applying array-processing methods can enhance arrivals reflected or converted near the core. Such reanalysis supplied evidence for a solid inner and fluid outer lunar core; its layer sizes remain an inference from a propagation model.^[ref]