Moonquakes are tremors at the Moon's surface. Because the Moon is so cold and rigid, these may reverberate on and on and last for over ten minutes (as opposed to 30 seconds on average on Earth).
According to the latest studies, there are four types of moonquake. These are:
- Deep moonquakes, which occur at 700 kilometres from the surface, and are probably due to tidal effects;
- "Thermal" moonquakes, the consequence of the dilatation of the crust, which expands when the surface is lit by the Sun following two weeks of penumbra and biting cold;
- Superficial tremors, which occur between 20 and 30 kilometres beneath the surface, and of which the causes are still little understood (some scientists think they are due to landslides near large craters).