The Moon Has Earthquakes — And They Last Longer Than Anything on Earth

We think of the Moon as the epitome of geological stillness. Airless, atmosphereless, lacking plate tectonics, its surface unchanged for billions of years except by the slow patter of meteorites. The craters we see through binoculars were formed billions of years ago; the footprints left by Apollo astronauts will persist unchanged for millions of years. The Moon, in this view, is geology's retirement community — a world where nothing exciting has happened in a very long time.

This view is not wrong, exactly. But it is incomplete. The Moon shakes. It shakes regularly, sometimes violently, and when it shakes, the trembling lasts for an extraordinarily long time — up to 10 minutes for a strong moonquake, compared to the 30 to 60 seconds that a major earthquake typically lasts on Earth. This difference in duration reveals something fundamental about the Moon's internal structure, and it has major implications for any human presence on the lunar surface.

The Apollo Seismometers

Our knowledge of moonquakes comes almost entirely from a remarkable array of scientific instruments left on the lunar surface during the Apollo missions. Between 1969 and 1972, Apollo astronauts placed five seismometers on the Moon — at the landing sites of Apollo 11, 12, 14, 15, and 16. These instruments were designed to detect any ground motion, however faint, and radio the measurements back to Earth.

The network operated until 1977, when it was shut down for budget reasons. In that time, it recorded approximately 12,500 moonquakes and impacts. The dataset was analyzed immediately and has been reanalyzed multiple times since as computing power and analytical methods have improved, with new discoveries emerging from the same data decades later.

What the seismometers found confounded initial expectations. The Moon was not geologically quiet. It was producing a steady stream of seismic activity, distributed across four distinct categories of events, each with its own mechanism and characteristic signature.

Types of Moonquakes

The four categories of moonquakes illuminate the surprisingly varied ways that a world can shake even without plate tectonics.

Deep moonquakes originate from approximately 700 kilometers below the surface — deeper than any earthquake on Earth, which rarely reach below 600 kilometers. They are the most numerous type, making up the majority of the 12,500 events recorded. Remarkably, they occur in clusters that are precisely correlated with the tidal forces exerted on the Moon by Earth and the Sun. As the Moon's orbit carries it closer to and farther from Earth, the tidal stress on its interior fluctuates, periodically squeezing the deep rocks until they slip. This tidal triggering makes deep moonquakes one of the most predictable geological events in the solar system.

Shallow moonquakes occur at depths of only 20 to 30 kilometers — far closer to the surface. They are the most powerful, with the strongest reaching magnitude 5.5 on the Richter scale — strong enough that a person on the surface would feel the ground move significantly. Shallow moonquakes are not as well understood as deep ones; their triggering mechanism remains a subject of research, though the release of accumulated tectonic stress in the Moon's outer shell is the leading hypothesis. The lunar reconnaissance orbiter has identified scarps — cliff-like features — on the Moon's surface that appear to be the geological signatures of recent thrust faulting, suggesting that the Moon's outer shell is slowly compressing as the interior cools.

Thermal moonquakes are among the most fascinating in their regularity. They occur at the lunar dawn, when the Sun first rises over the surface after the two-week lunar night. The Moon's surface temperature swings wildly — from about -173°C (-280°F) during the night to as high as 127°C (261°F) in direct sunlight. This enormous temperature change causes the surface rocks and structures to expand and contract, generating small but detectable seismic signals as rock faces crack and shift. The regularity is so precise that seismologists can set their watches by the timing of thermal moonquake clusters.

Meteorite impacts are the fourth category — the Moon's lack of atmosphere means that every space rock, from dust grains to boulders, strikes the surface at full cosmic velocity. The seismometers detected thousands of these impacts and provided scientists with a continuous census of meteorite flux at the lunar surface.

Why Do Moonquakes Last So Long

The most striking characteristic of lunar seismicity is the duration of shaking. When a significant moonquake occurs, the seismic waves it generates travel through the lunar interior and surface and keep bouncing and reverberating for periods of up to 10 minutes. The seismogram of a strong moonquake shows a gradual buildup in amplitude over the first minute or two, followed by an extended decay that slowly fades over many more minutes. An equivalent earthquake would reach its peak quickly and die away in under a minute.

The explanation lies in the fundamental difference in geological structure between Earth and Moon. Earth's interior is "wet" — not literally filled with water, but pervaded with fluids, partially molten rock, and materials with significant internal friction. When seismic waves travel through Earth's interior, they lose energy rapidly because the material they pass through absorbs and dissipates the wave energy. The waves are damped.

The Moon's interior, by contrast, is dry, cold, and rigid to an unusual degree. The deep lunar rocks are almost completely free of water and fluids, and they have been cold and solid for billions of years. When seismic waves enter this rigid, undamped material, there is very little to absorb them. They bounce off boundaries between rock layers, scatter off buried impact craters, and refract through density gradients, bouncing around the interior for minutes like sound bouncing around an empty cathedral. The Moon rings like a bell.

This analogy — the Moon as a giant bell — was actually used by astronaut and scientist Harrison Schmitt, the Apollo 17 lunar module pilot and the last human to walk on the Moon. After the ascent stage of the Apollo 12 lunar module was deliberately crashed into the Moon at the end of that mission, the seismometer recorded shaking that lasted for approximately 55 minutes, leading scientists to famously say that the Moon rang like a bell.

What This Means for Lunar Colonization

For the architects of any future permanent human presence on the Moon, moonquake research carries practical urgency. A magnitude 5.5 shallow moonquake is not trivial — it is strong enough to topple structures, crack pressure vessels, and damage equipment. And unlike earthquakes, which typically last less than a minute, the prolonged shaking of a major moonquake means sustained stress on any structure through extended cycles of vibration.

The deep correlation between tidal forces and deep moonquakes means that the seismic risk is somewhat predictable — engineers can know in advance that certain orbital configurations will produce elevated moonquake activity. The unpredictability of shallow moonquakes is more concerning; their triggering mechanism is not well enough understood to forecast them reliably.

Designing lunar habitats to withstand sustained seismic shaking while maintaining pressure integrity and structural strength is a genuine engineering challenge that current lunar architecture proposals must address. The Moon may be geologically quieter than Earth, but it is not geologically silent — and any structure we build there will need to survive its long, slow ringing.