Seismometers that Apollo astronauts placed on the surface of the Moon have revealed that the Moon experiences moonquakes.

Deep moonquakes, occurring hundreds of miles beneath the lunar surface, are tidal events -- they result from the pull of Earth's gravity tugging and stretching the Moon's internal structures. Another type of moonquake is caused by the Moon shrinking as it cools -- a process that has been happening since the Moon first formed nearly 4.5 billion years ago. These moonquakes originate at the moderately shallow depths of 20-30 km, can register up to a startling 5.5 on the Richter scale, and can last for over 10 minutes! Meteoroid impacts with the Moon can cause moonquakes originating on or near the lunar surface. Another type of extremely shallow moonquake can come from thermal expansion and contraction of rock on or near the surface as it goes from the frigid lunar night to the very hot lunar daytime.