Moon rocks on
well as impact events, the Moon is also rocked by
‘moonquakes’, the lunar equivalent of earthquakes.
are four different types of moonquake. Deep moonquakes occur up to 700
kilometres below the Moon’s surface and are a result of tidal
stresses caused by the gravitational tug of war between the Earth, Moon
and Sun. Shallow moonquakes occur at the surface and down to depths
less than about 20 or 30 kilometres, and are often due to landslides of
rock down steep crater rims. The Moon also suffers from thermal
moonquakes, which occur when the freezing crust expands as it returns
into sunlight after two weeks of lunar night time. Meteorite moonquakes
can also cause a rumble or vibration of the surface when a meteroid
slams into the surface.
Moonquakes are much
than earthquakes and, apart from the shallow quakes, are also much
weaker than the killer earthquakes we have experienced on Earth.
Experiments conducted by the Apollo astronauts measured shallow
moonquakes reaching the equivalent of 5.5 on the Richter scale, with
surface vibration occurring for many minutes longer than on the Earth,
which would cause damage to buildings on the Earth. Future lunar
settlers will have to be careful that they build strong enough houses
and observatories for their telescopes to withstand these shallow
The lunar seismometer
(lower right) carried aboard Apollo 16.