Moonquakes: Seismic Ringing of a Dry, Fractured Moon

Trigger a Seismic Event

Regolith & Source

Seismic quality factor Q 3000

Magnitude 4.5

Playback speed 30×

Live Readouts

Time since event0:00

Amplitude at Apollo site0%

Predicted coda duration—

How it works

Apollo seismometers found that moonquakes and meteorite impacts make the Moon "ring like a bell" for up to several hours, while a similar Earth quake dies out in minutes. The cause is the Moon's megaregolith: kilometres of bone-dry, impact-fractured rock that scatters seismic waves instead of absorbing them, so energy bounces around long after the source has gone quiet.

This is captured by the seismic quality factor Q — how many oscillation cycles a wave survives before its energy drops by 2π. Lunar rock reaches Q ≈ 3000–5000; wet, jointed Earth rock is typically Q ≈ 50–300. The envelope of ground motion at distance r and time t after arrival follows:

A(r,t) = (E₀ / r) · exp( -π·f·t / Q ) · sin(2π·f·t + φ₀)
τ₊₅ (coda duration to 5% of peak) ≈ 3·Q / (π·f)

Each scatter point on the Moon's surface below is a small seismometer: when the wavefront (great-circle distance ÷ wave speed) reaches it, it lights up and rings down at the rate this Q sets — the higher the slider, the longer the shimmer keeps spreading after the flash has passed.

Shallow moonquake — tectonic slip a few km down; sharp, higher-frequency source.
Deep moonquake — tidal flexing ~700–1200 km down, tied to Earth's tidal pull; weaker at the surface, lower frequency.
Meteorite impact — largest initial energy, very short pulse, richest in high frequencies.
Apollo site marker — a fixed reference point (near Apollo 12/14/15/16's seismometer network) whose live trace is drawn on the strip chart below.

Real-world relevance: this scattering/ringing behaviour is exactly why lunar-base engineers plan structures for long-duration low-amplitude shaking rather than a single sharp jolt, and why NASA's proposed Farside Seismic Suite would need months of listening to map the deep interior.

Scattered seismic energy Event source Apollo seismometer site

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