Some shallow moonquakes recorded during the Apollo programme were likely caused by tectonic activity, according to a paper published online this week in Nature Geoscience.
The discovery of young faults less than 50 million years old on the Moon by the Lunar Reconnaissance Orbiter Camera in 2010 has been interpreted as evidence of lunar tectonic activity. However, it is unclear how recent this activity is.
Thomas Watters and colleagues examined 28 moonquakes recorded by seismometers at four Apollo landing sites (12, 14, 15 and 16) from 1969 to 1977. Using an algorithm for sparse seismic networks, the authors were able to improve estimates of the epicentre locations of these moonquakes. They found that seven shallow moonquakes fell within 60 km (five of those within 30 km) of young fault scarps (cliff-like landform caused by horizontal contraction of the Moon’s surface), and occurred during peak tidal stress when a fault slip event was most likely. The authors conclude that the proximity of moonquakes to fault scarps, together with boulder movement and disturbance of the regolith (the upper layer of loose soil), suggest that the Moon is currently tectonically active.