Published: Tue, May 14, 2019
Research | By Raquel Erickson

The moon is a lot more seismically active than we thought

The moon is a lot more seismically active than we thought

As the moon cools and gets smaller, its crust becomes brittle and breaks up: a bit like what happens to a grape as it dries out to become a raisin.

These faults push one part of the lunar crust up and over the adjoining part, said University of Maryland geologist and study co-author Nicholas Schmerr. When portions of the crust split they move over neighbouring sections of the surface, triggering earthquakes, or rather, moonquakes.

"We think it's very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces, indicating that the Apollo seismometers recorded the shrinking moon and the moon is still tectonically active", said Thomas Watters, lead author of the paper and a senior scientist at the Smithsonian Institution. Each of the magnitudes of the 28 moonquakes would register as somewhere between two and five on the Richter scale if they had been carried out on Earth.

One of the thrust faults discovered by NASA's Lunar Reconnaissance Orbiter.

Resembling stair-shaped cliffs, the fault scarps are tens of metres high and extend for several kilometres.

These incredible findings were published today (May 13) in the journal Nature Geosciences.

Astronauts from NASA's Apollo 11, 12, 14, 15 and 16 left behind seismometers on the Moon to scan the lunar orb for tectonic activity. Seismometers are instruments that measure the shaking produced by quakes, recording the arrival time and strength of various quake waves to get a location estimate, called an epicenter.

Watters and his team also looked carefully at data from the Lunar Reconnaissance Orbiter and identified areas near the faults that look like they've been recently disturbed - boulders that have rolled in the near past, or evidence of landslides. But the lunar faults, like Earth's own fault lines, are similar in that occur where pieces of the surface sometimes rub against each other, causing quakes that can reverberate throughout the planet. The researchers ran 10,000 simulations to calculate the chance of a coincidence producing that many quakes near the faults at the time of greatest stress. Researchers re-analyzed seismic data they had from the moon to compare with the images gathered by the orbiter.

John Keller of NASA's Goddard Space Flight Center said: "It's really remarkable to see how data from almost 50 years ago and from the LRO mission has been combined to advance our understanding of the Moon while suggesting where future missions intent on studying the Moon's interior processes should go". Researchers suggested these faults were evidence of lunar tectonics, although it was unclear how recent this activity was.

Important as this discovery is, scientists think the moon isn't the solar system's only object shrinking with age. The innermost planet Mercury boasts numerous thrust faults.

The LRO has imaged more than 3,500 fault scarps on the moon since it began operation in 2009.

NASA's next mission to the Moon will be called Artemis, the USA space agency announced Monday, though it's still looking for the money to make the journey happen by its accelerated 2024 deadline.

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