> The discovery of young thrust faults on the Moon is evidence of recent tectonic activity, but how recent is unknown. Seismometers at four Apollo landing sites recorded 28 shallow moonquakes between 1969 and 1977. Some of these shallow quakes could be associated with activity on the young faults. However, the epicentre locations of these quakes are poorly constrained. Here we present more-accurate estimates of the epicentre locations, based on an algorithm for sparse seismic networks. We found that the epicentres of eight near-surface quakes fall within 30 km of a fault scarp, the distance of the expected strong ground shaking. From an analysis of the timing of these eight events, we found that six occurred when the Moon was less than 15,000 km from the apogee distance. Analytical modelling of tidal forces that contribute to the current lunar stress state indicates that seven near-apogee events within 60 km of a fault scarp occur at or near the time of peak compressional stresses, when fault slip events are most likely. We conclude that the proximity of moonquakes to the young thrust faults together with evidence of regolith disturbance and boulder movements on and near the fault scarps strongly suggest the Moon is tectonically active.
Thanks. It's based on the following data (from the same link):
"Lunar seismicity was recorded by four seismometers placed at the Apollo 12, 14, 15 and 16 landing sites. These seismometers operated from 1969 to 1977 and recorded 28 shallow moonquakes."
and it's a more modern and definitely interesting approach to analyze these measurements. The conclusion which "strongly" suggests that "the Moon is tectonically active" is an argument to measure more in the future. The new measurements and the refinement of their analysis could surely increase our capabilities of modelling the rocks and the layers, even on the Earth. It doesn't however mean that the structure of the Moon fully matches that of Earth.
"The team's findings suggest the moon possesses a solid, iron-rich inner core with a radius of nearly 150 miles and a fluid, primarily liquid-iron outer core with a radius of roughly 205 miles. Where it differs from Earth is a partially molten boundary layer around the core estimated to have a radius of nearly 300 miles."
> Furthermore, shallow moonquakes lasted a remarkably long time. Once they got going, all continued more than 10 minutes. "The moon was ringing like a bell," Neal says.
Didn't people believe at some point that moon landings themselves caused the Moon to vibrate or something along those lines? Always found that eyebrow-raising.
You might be thinking of impactor probes, in which a vehicle is deliberately crashed into the moon (or another body) in order to generate shockwaves. Previously landed seismic instruments can us this to gather information about the moon's internal structure.
There is a "hollow moon" conspiracy theory where one of the pieces of evidence cited is that the moon rang like a bell because of the impact of the lander.
As I understand it, the fact that the moon is tectonically active implies that there still is enough heat in the moon's core to cause tectonic activity.
The article talks about these movements occurring close to apogee (the point in the Moon's orbit when it's furthest from the earth), so it looks like this activity is driven by gravitational tidal forces rather than internal heat.
"Even when there's no water to respond to tidal forces, the solid mass of a planet feels the stress caused by these forces. In fact, tidal forces can heat the interior of a satellite in an elliptical orbit. In that case, the satellite comes closer to the planet during one part of its orbit and there it's subjected to strong stretching forces. As it moves away from the planet the stress is partly released and the body relaxes back toward a more spherical shape. This continual flexing of the satellite creates heat through internal friction, in the same way, that if you flex a tennis ball enough times it becomes warm. This effect is called tidal heating. The more elliptical the orbit, the stronger the tidal heating. Jupiter's large Galilean satellites experience this kind of heating — enough to produce extensive volcanism on Io and possibly create liquid-water oceans beneath the surface of Europa."
The question is how the Moon could be more precisely modeled, and if some refinements to our models used on Earth too could be done, and for all that more measurements would be needed. The paper uses only those made from 1969 to 1977 from the seismometers placed by four Apollo missions, and tries to interpret the data with newer methods than what was done before with the existing measurements, but since 1977 there were no new measurements.
"About 50% of the heat given off by the Earth is generated by the radioactive decay of elements such as uranium and thorium, and their decay products. That is the conclusion of an international team of physicists that has used the KamLAND detector in Japan to measure the flux of antineutrinos emanating from deep within the Earth."
I’m a bit out of my depth here, so someone more knowledgeable correct me if my understanding is wrong.
In the article, they’re stating they believe it’s seismic activity because it’s occurring within some distance of these fault scarps, which also appear to be where the surface displays lines in the images shown in the article?
How are they dismissing it’s not a result of material from space striking the surface? Is it that their sensors are able to disambiguate if the source is from the surface vs deeper in the moon?
I think quakes last noticeably longer than impacts, at least if they are large enough. On Earth, there's a fairly well-established empirical correlation[1]. Putting a magnitude of 5.5 into the formula given here suggests a duration of about 70s, if that relationship holds on the Moon.
> How are they dismissing it’s not a result of material from space striking the surface?
The earthquakes are magnitude 5.5, plugging that into an energy calculator (http://earthalabama.com/energy.html#/) gives a result of 0.2 Hiroshima bombs, which I think would be noticeable.
>> 0.2 Hiroshima bombs, which I think would be noticeable.
Maybe not. Hiroshima wasn't all that big on geological scales. A medium-sized meteor stroking the moon would have equivalent energy. Tidal forces can also break meteors up, spreading them into streams of smaller bits that land over a period of time. So I am not so dismissive of potential impacts.
Yes, you can estimate the depth below the surface by reading the seismic arrival times. There are compressional waves that travel along the surface, which travel at different speeds than the pressure and compressional waves going straight through the moon.
In south- and east-asia mythology a frog lives in the moon.
This is part of an australian aboriginal myth:
"The frog opened his sleepy eyes, his big body quivered, his face relaxed, and, at last, he burst into a laugh that sounded like rolling thunder. The water poured from his mouth in a flood. It filled the deepest rivers and covered the land. Only the highest mountain peaks were visible, like islands in the sea. Many men and animals were drowned.
The pelican-who was a blackfellow at this time -sailed from island to island in a great canoe and rescued any blackfellow he saw" - http://www.sacred-texts.com/aus/mla/mla09.htm
moon worms! joking aside reminds me very much of 50s sci-fi - maybe there will be a mining operation to draw energy from the moon's core in the near future (owned by Jeff Bezos)
Moonworms are gentle, misunderstood creatures that have been horribly exploited by mankind.
These majestic beasts are captured when young, and through a process involving electric shock and sub-nuclear bombardment trained to perform tricks for the amusement of lunar tourists who often like to ride on top of their backs and put pictures of their abuse onto Facebook for exploitative likes.
Please donate 100 credits to Save the Moonworm - an offplanet non-profit organized by the head of Jeff Bezos.
“Without water, the lunar surface instead gets deformed, stretching from a spherical shape into a more oblong one and back again.”
Is enough energy to keep the core of the moon hot? Like maybe the moons mass alone for for 4+ billion years would have cooled but the additional force of the earth stretching the moon like a rubber band creates heat energy...
> The discovery of young thrust faults on the Moon is evidence of recent tectonic activity, but how recent is unknown. Seismometers at four Apollo landing sites recorded 28 shallow moonquakes between 1969 and 1977. Some of these shallow quakes could be associated with activity on the young faults. However, the epicentre locations of these quakes are poorly constrained. Here we present more-accurate estimates of the epicentre locations, based on an algorithm for sparse seismic networks. We found that the epicentres of eight near-surface quakes fall within 30 km of a fault scarp, the distance of the expected strong ground shaking. From an analysis of the timing of these eight events, we found that six occurred when the Moon was less than 15,000 km from the apogee distance. Analytical modelling of tidal forces that contribute to the current lunar stress state indicates that seven near-apogee events within 60 km of a fault scarp occur at or near the time of peak compressional stresses, when fault slip events are most likely. We conclude that the proximity of moonquakes to the young thrust faults together with evidence of regolith disturbance and boulder movements on and near the fault scarps strongly suggest the Moon is tectonically active.
[1] https://www.nature.com/articles/s41561-019-0362-2