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Space shocker: Earth's moon is shrinking, experiencing seismic activities

14 May 2019

Scientists know the Moon is too cold and still to have plate tectonics, like Earth, which keeps our whole crust sliding around in giant, continent-sized pieces. However, the moon is much smaller than Earth and therefore largely cooled off long ago, so one might not expect much, if any, tectonic activity. These faults resemble small stair-shaped cliffs, or scarps, when seen from the. New research suggests that these faults may still be active. The moon has gotten about 150 feet skinnier over the last few hundred million years.

The findings suggested that these "cliffs", or thrust faults, had formed as a result of tectonic activity related to the moon contracting in size as it cooled.

Seismometers at four Apollo landing sites on the moon recorded 28 shallow moonquakes between 1969 and 1977, ranging from magnitude 1.5 to 5 on the Richter scale. At least eight of the quakes occurred due to activity along the faults.

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These freaky moonquakes were detected by five seismometers placed on the lunar surface during the Apollo 11, 12, 14, 15, and 16 missions. These tracks are evidence of a recent quake because they should be erased relatively quickly, in geologic time scales, by the constant rain of micrometeoroid impacts on the Moon.

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. To do so, the scientists relied on analytical techniques developed to interpret data from sparse networks of seismometers on Earth. Researchers made this conclusion after analysing images taken by NASA's Lunar Reconnaissance Orbiter. Schmerr designed the algorithm that re-analyzed the Apollo data.

Using the revised location estimates from their new algorithm, the researchers found that the epicenters of eight of the 28 shallow quakes were within 19 miles of faults visible in the LRO images.

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Some of the quakes also happened during a point in the moon's orbit when it was farthest from Earth, indicating that the tidal stress of Earth's gravity could have contributed to stress on the moon's crust.

"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", said Thomas Watters of the Smithsonian Institute, lead author of a paper on the findings published in Nature Geoscience on Monday.

As the moon's interior cools, it shrinks, which causes its hard surface to crack and form fault lines, according to research sponsored by NASA. However, unlike the flexible skin on a grape, the moon's crust is brittle, causing it to break, resulting in faults.

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"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", said LRO Project Scientist John Keller of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It is also a testament to how much can be gained by human spaceflight to the surface of other worlds and underlines the unbelievable potential for future missions back to the moon and, hopefully someday, Mars".