Moonquakes

The Moon is still losing heat and, as a result, shrinking slightly. This shrinking, plus the stress on the Moon’s outer layer produced by the tugging of Earth’s gravitational pull, cracks the Moon's crust.

Moonquakes

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.

An astronaut stands on the Moon. He is in a spacesuit and his back is facing the camera. On his right is a copper-colored metal drum with two solar panel arrays on the left and right, extended like wings. A laser reflector is beyond the drum. Going backwards into the image, the lunar module stands on four legs and is copper and silver. Further back, an American flag is planted into the dusty Moon.
Astronaut Buzz Aldrin deploys a seismic experiment during the Apollo 11 moonwalk. The experiment contained four seismometers powered by two panels of solar cells.
NASA

A Shrinking Moon

Cliffs in the lunar crust, observed by the Apollo astronauts and by NASA’s Lunar Reconnaissance Orbiter, indicate that the Moon shrank globally in the geologically recent past and is likely still shrinking today. The Moon formed in a chaotic environment of intense bombardment by asteroids and meteors. These collisions, along with the decay of radioactive elements, made the Moon hot. Since its inception, the Moon has been cooling. As it cools, it shrinks and its brittle surface breaks, forming thrust faults where a section of the crust breaks away from and juts out over another. Scientists estimate that, in the last several hundred million years, the diameter of the Moon has gotten about 150 feet (50 meters) smaller.

A grayscale image of a long, sinuous, rounded cliff running from the bottom left to the top right. The view is from overhead at an angle, not directly overhead.
A thrust fault along the wall of Slipher crater, near the Moon’s north pole. The cliff is about 20 meters high/65 feet high, which is nearly as tall as a five-story building. This view of Slipher crater was made by compiling images from the Lunar Reconnaissance Orbiter Camera into high-resolution topographic maps, called digital elevation models (DEMs). Software can be used to view the DEM from any perspective.
NASA/GSFC/Arizona State University.
Keep Exploring

Discover More Topics from NASA

Moon Water and Ices

Composite image of a Moon's crater with superimposed illustration of a blue-green pool of water.

Moon Formation

Illustration of a smaller grey rock colliding into another larger rock in space.

Moon Composition

Illustration of the schematic cross sections of the Earth's Moon inner layers.

Weather on the Moon

Render of the Moon's surface and the Sun