During the NASA Apollo missions, astronauts installed seismometers on the near side of the Moon to record moonquakes. The instruments transmitted continuous seismic data to the Earth between July 1969 and September 1977. Early analysis identified four types of natural moonquakes: meteoroid impacts, thermal moonquakes, shallow moonquakes, and deep moonquakes.
Seismic interferometry has been applied previously to study the internal structure of the Earth. This was the first time that the technique has been applied to investigate deep moonquakes to examine the Moon’s internal structure.
The team identified the lunar seismic Moho (Mohorovičić discontinuity, the boundary between the crust and the mantle). The results reveal a layer at a depth of about 50 km below the Apollo seismic stations. This information provides an independent estimate of the thickness of the lunar crust. Knowledge of the crustal thickness is important for understanding the genesis and history of the Moon. It has implications for bulk composition, the origin of Moon rocks, and other aspects of lunar evolution. The authors suggest that deep moonquake seismic interferometry could be extended to imaging the subsurface below seismic stations on the far side of the Moon if future missions install them.
The results of this study reveal a laterally coherent acoustic boundary at a depth of about 50 km below the Apollo seismic stations, which the researchers interpreted as the lunar seismic Moho. The information provides an independent estimate of the thickness of the lunar crust.
NNSA sponsored the Los Alamos portion of the research. Capabilities developed and used in this analysis support the Laboratory’s Global Security mission area and the Science of Signatures science pillar through the ability to investigate earth structure and determine the location and magnitude of earthquakes and underground explosions.