Shrinking Moon May Be Generating Moonquakes

Robert Zwilling

Well-Known Member
Jun 12, 2018
Shrinking Moon may be generating Moonquakes
New analysis of the original seismic data from 50 years ago combined with more recent pictures from the Reconnaissance Orbiter Camera paint a picture of a slowly shrinking moon. The original quake data from instruments setup by astronauts measured quakes that ran from 2 to 5 on the Richter scale. Between 1969 and 1977 28 shallow quakes were detected. Unlike the Earth the quakes seem to be clustered around easily visible faults on the Moon's surface making it a simple matter to avoid building in quake zones. A quake with a reading of 5 probably wouldn't be a good thing to experience in a flimsy Moon building. Apparently no more seismographs have been placed on the Moon since the astronauts set up the original devices. Supposedly the quakes are more likely when the Moon is farthest away from the Earth which is a yearly event. They could be the result of gravitational stress caused the Earth's tides. The ocean water is slowly growing in mass and shape as the Polar regions melt which might make the tidal pulls stronger or more likely to trigger stronger quakes. Since the next manned explorations are scheduled for 2022 it might be a good idea to get a better idea of what the Moon is up to seismically speaking. .
Interesting but a couple of corrections. The moon will reach it's apogee once every orbit or once every lunar month not once a year. Also I don't think the there is anything to indicate Earth's ocean tides have anything whatsoever to do with this. The variation in tidal forces they are discussing are, I think, the variations in gravitational force caused by changes in the distance from Earth.
That would make it far more often than I was supposing. The only good thing that could come out of that would be the that a quake in low gravity is a lot less violent than one in a higher gravity situation. Would astronauts working on the Moon need quake proof as well as dust proof structures. Mapping out the distribution and depth of the fault patterns might be useful for determining the best places to build on the Moon. It would be interesting to know how the dates of the recorded moonquakes corresponded to our lunar visits and if the polar regions where there could be more water and more human activity are less likely to have moonquakes.

Lunar recession seems to be a combination of factors that are partially effected by the position of continents, the movement of the water across the planet, the tidal bulge, and the passage of time. The bulge transfers energy to the moon, making it pull away from the Earth by a very amount, slightly speeding up the Moon. At the same time the tides are slowing the Earth down, which has to be slowing the Moon down as well. The size of the bulge could be be a very small factor on the stress of the Moon's surface. The rate of the rise of the bulge could possibly increase or decrease in a non linear amount compared to the average sea level increase. The problem still remains that the Moon is slowly being squeezed by the Earth every time it goes around it which could be giving the faults on the moon the energy they need to move in absence of any plate tectonic forces. Earthquakes can be good news bearing events for scientists but bad news for people where they happen.

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