The Moon Has Moonquakes

One of the key scientific legacies of the Apollo missions was the discovery that the Moon isn't a geologically silent world. Astronauts on four separate missions deployed sensitive instruments called seismometers, which operated for years after the crews returned home. Between 1969 and 1977, this network (Review) listened to the Moon's interior and detected thousands of seismic events, revealing a world with a surprising amount of activity hidden beneath its quiet surface.

These "moonquakes" come in several varieties. Some are deep tremors caused by the gravitational tug of the Earth, while others are triggered by meteoroid impacts or the thermal stress of the lunar crust expanding and contracting as it heats and cools. The most powerful, though rare, are shallow quakes that can register up to 5.5 on the Richter scale. Unlike earthquakes, which are quickly dampened by Earth's water and fractured geology, moonquakes can reverberate for extended periods. The Moon's dry, rigid structure lacks these dampening materials, causing it to ring like a bell, with some vibrations lasting for up to ten minutes.