Overlooked Apollo data from the 1970s reveals huge record of 'hidden' moonquakes

The moon is much more seismically active than we realized, a new study shows. A reanalysis of abandoned data from NASA's Apollo missions has uncovered more than 22,000 previously unknown moonquakes — nearly tripling the total number of known seismic events on the moon. 

Moonquakes are the lunar equivalent of earthquakes, caused by movement in the moon's interior. Unlike earthquakes, these movements are caused by gradual temperature changes and meteorite impacts, rather than shifting tectonic plates (which the moon does not have, according to NASA). As a result, moonquakes are much weaker than their terrestrial counterparts.

Between 1969 and 1977, seismometers deployed by Apollo astronauts detected around 13,000 moonquakes, which until now were the only such lunar seismic events on record. But in the new study, one researcher spent months painstakingly reanalyzing some of the Apollo records and found an additional 22,000 lunar quakes, bringing the total to 35,000. 

The findings were presented at the Lunar and Planetary Science Conference, which was held in Texas between March 13 and March 17, and are in review by the Journal of Geophysical Research.

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The newly discovered moonquakes show "that the moon may be more seismically and tectonically active today than we had thought," Jeffrey Andrews-Hanna, a geophysicist at the University of Arizona who was not involved in the research, told Science magazine. "It is incredible that after 50 years we are still finding new surprises in the data."

Apollo astronauts deployed two types of seismometers on the lunar surface: one capable of capturing the 3D motion of seismic waves over long periods; and another that recorded more rapid shaking over short periods.