Earth’s moon is shrinking and quaking, study says

Additionally, "Establishing a new network of seismometers on the lunar surface should be a priority for human exploration of the Moon, both to learn more about the Moon's interior and to determine how much of a hazard moonquakes present", said co-author Renee Weber, a planetary seismologist at NASA's Marshall Space Flight Center in Huntsville, Alabama.

By looking at the size and location of the tremors, the algorithm estimates the epicenter of the moonquakes.

Although the Apollo instruments recorded their last quake shortly before the instruments were retired in 1977, the researchers suggest that the moon is likely still experiencing quakes to this day.

Researchers examining the seismic data gathered during NASA's Apollo missions traced the location of some of the quakes to step-shaped cliffs called scarps on the lunar surface that formed relatively recently, in geological terms, due to the ongoing subtle shrinking of the moon as its hot interior cools. "It's quite likely that the faults are still active today".

Since the moon's crust is brittle, these forces cause its surface to break as the interior shrinks, resulting in so-called thrust faults, where one section of crust is pushed up over an adjacent section.

A team of geologists believe these cliff-like features are evidence of lunar tectonic activity. Some of these shallow quakes might in theory result from activity on lunar faults, but the locations and depths of the sources of these quakes were uncertain.

Watters said some of the quakes "can be fairly strong" - as high as a 5 on the Richter scale.

For example, the Apollo missions detected about 11,000 moonquakes happening about 500 to 680 miles (800 to 1100 kilometers) beneath the lunar surface. Those missions even saw artificial moonquakes from the impacts of the spacecraft used to bring astronauts to the moon, Schmerr added.

Six out of the eight tectonically active moonquakes occurred when the Moon was at or close to its apogee, the point where it's most distant from Earth and where the diurnal and recession stresses create the most compression near the tidal axis. A team of researchers have now reanalyzed the data along with detailed images captured by the Lunar Reconnaissance Orbiter, which was launched in 2009.

"It is truly fantastic that the datasets collected by the astronauts so many years ago are still yielding new scientific findings about our moon", Schmerr said. The agency will establish sustainable missions by 2028, then we'll take what we learn on the Moon, and go to Mars.

This Lunar Reconnaissance Orbiter Camera (LROC) picture shows a prominent lunar lobate thrust fault scarp.

The research paper, "Shallow seismic activity and young thrust faults on the Moon", Thomas Watters, Renee Weber, Geoffrey Collins, Ian Howley, Nicholas Schmerr and Catherine Johnson, was published in the journal Nature Geoscience on May 13, 2019. "It is also a testament to how much can be gained by human spaceflight to the surface of other worlds and underlines the incredible potential for future missions back to the moon and, hopefully someday, Mars".

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