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Does the Moon, through factors like its location (if it is at an apsis i.e closest point or furthest point in its orbit) or some changes in density, affect earthquakes on the Earth?

Earthquakes are a consequence of moving tectonic plates. And when a tectonic plate slides under another one in a subduction zone or two plates crash into each other in convergent zones or two plates diverge, earthquakes can happen. So I am wondering if the Moon's gravitational/tidal forces (e.g. tidal heating, which causes the interior of some celestial bodies to get hotter due to tidal friction) can cause perturbations on seismic activity which may influence the timing/strength of earthquakes? And how would I calculate those perturbations in the the seismic activity posed by the Moon?

This article states that the effect is small but I want to find out how much small the effect is.

JeopardyTempest
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    A few corrections. Not all earthquakes occur at plate boundaries, they can also occur inside tectonic plates due to stresses within plates. The perfect example of this is Australia, 1, 2. It lies within a tectonic plate but experiences numerous earthquakes, some significant. ... – Fred Jan 12 '23 at 01:43
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    ... Not all tectonic plates slide under each other (subduct), some crash into each other causing uplift, see the Himalayas. Other plates slide laterally against each other & others diverge, as occurs at the mid Atlantic ridges. Each generates its own system of earthquakes/tremors. Major earthquakes occur, not just because of sliding, but because snags along the boundaries break, release large amounts of stored energy. – Fred Jan 12 '23 at 01:51
  • Thanks, @Fred, Right. –  Jan 12 '23 at 05:32
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    Several recent studies, however, have found a correlation between earth tides (caused by the position of the moon relative to the earth) and some types of earthquakes. One study, for example, concludes that during times of higher earth and ocean tides, such as during times of full or new moon, earthquakes are more likely on shallow thrust faults near the edges of continents and in (underwater) subduction zones. Lunar or solar eclipses represent, of course, special cases of full and new moon, but do not cause any special or different tidal effects from full and new moon. –  Jan 12 '23 at 10:52
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    Source: USGS –  Jan 12 '23 at 10:52
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    Thanks, @Universal_learner –  Jan 12 '23 at 14:33
  • @ScienceAJ You are welcome and welcome to Stack Exchange Earth Science! –  Jan 14 '23 at 13:41
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    Thanks a lot, @Universal_learner –  Jan 14 '23 at 13:46
  • Seems to be a duplicate of Does the moon have any affect on earthquakes being created? which was deemed a duplicate of Relationship between tides and earthquakes. – justCal Jan 14 '23 at 18:29
  • Yes, @justCal. The seemingly duplicate that was deemed a duplicate does not answer my question. But the seemingly duplicate does answer my question to some extent. Like I got to know How to calculate it but however I'm not sure whether I can calculate the exact Richter scale –  Jan 15 '23 at 05:45
  • See: https://en.wikipedia.org/wiki/Tidal_triggering_of_earthquakes – Nilay Ghosh Jan 15 '23 at 10:29
  • Thanks, @NilayGhosh. But the Moon's gravity also does tidal heating and compresses and decompress the core of the Earth as provided by ArktourosUltorMaximus7600's excellent answer, so during a Sygyz, an earthquake should be of greater magnitude. Also is there any equation for the same? –  Jan 15 '23 at 10:59
  • I don't think there is a full-proof equation for this and although technically there should be a connection between tidal tides and plate tectonics movement but establishing the connection is too complicated as of now (the USGS article do mention some equation). You can also refer to the linked questions as it might answer your question. – Nilay Ghosh Jan 16 '23 at 05:58
  • Thanks, @NilayGhosh –  Jan 16 '23 at 06:03

1 Answers1

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Actually, yes, but indirectly

Well, the tidal forces produced by the Moon's gravity are not enough to distort the Earth's crust enough to produce any significant displacements of the crust, and produce earthquakes. The only significant effect would be producing tides on the ocean. Remember the crust is rigid, whereas water is not.

However, the Moon's gravity does warm up the Earth's core up to some degree, due to the continuous squeezing and stretching of the Earth (Most of the internal heat comes from radioactive decay and heat from the formation of the planet). It is this warmth, that drives tectonic plates, and thus ultimately, earthquakes.

EDIT: Crustal tides are indeed produced by the Moon's gravity. In fact, this effect causes New York to rise and sink by 14 inches in a day. But this effect is too smooth. You cannot perceive this effect with the naked eye. Crustal tides are not violent, rapid events. They occur gradually throughout the day. On the other hand, Earthquakes are produced by many reasons, most common being the sudden release of pressure and energy by tectonic plates, in just a fraction of a second. This sudden release of energy triggers vibrations in the plates, which we call Earthquakes.

Lunar gravity is simply not strong enough to trigger massive and rapid disturbances in the crust to create Earthquakes of sufficient magnitude. Even if it did happen, it would mostly be restricted to Magnitude 0-2 on the Modified Mercalli Scale, which can barely be noticeable to humans.

The only place where gravity/tidal forces can trigger powerful earthquakes would be a moon of Jupiter, Io. Io's interior, which is already under massive stresses from Jupiter's gravity, can find itself further distorted by combined gravitational forces from Ganymede, Callisto and Europa, which can trigger massive earthquakes (Ioquakes?) and of course, volcanoes.

Alastor
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  • Thanks a lot!.. –  Jan 12 '23 at 14:31
  • So at Periapsis, What Richter scale Earthquake would it be? –  Jan 12 '23 at 15:04
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    The crust may be strong, but it is not rigid. The daily crustal tide can be measured and may be larger than most imagined. See https://science.howstuffworks.com/environmental/earth/geology/rising-rock-earths-crust-has-its-own-tides.htm – JohnHoltz Jan 12 '23 at 15:30
  • Thanks, @JohnHoltz. So if the Moon is at some Apsis i.e nearest or closest point in an orbit or has some changes in density (though Gravity is not due to Density, Density plays a role), How much would the Crust's Tectonic plates get displaced? and How much Richter scale Earthquake would it cause? –  Jan 12 '23 at 15:36
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    Asking the size of the earthquake the moon would trigger is a little like watching a small disturbance trigger a mousetrap and asking how violent the mousetrap was. – mmesser314 Jan 12 '23 at 22:07
  • @ScienceAJ it depends. Gravitational Earthquakes (tidal earthquakes for laymen) are not strong enough on average, compared to earthquakes produced by Tectonic stresses and activity. True, crustal tides may cause New York to rise and sink by 14 inches, but the effect is so smooth, that it is straight up impossible to detect them with the naked eye, unless you use some scientific instruments. On the other hand, earthquakes are rapid, not-too-smooth events, which you can easily notice, which are produced due to a variety of reasons, most common being the sudden release of tectonic stress. – Alastor Jan 14 '23 at 08:46
  • Thanks (+1), @ArktourosUltorMaximus7600. So how do I calculate the displacement of Tectonic plates near Subductions zones due to Crustal tides like you've done by calculating the New York city to rise and sink by 14 inches (I know it would need a lot of data like the weight of the tectonic plate, position of the moon, etc..)? –  Jan 14 '23 at 08:57
  • I could quite reasonably envision that the stress builds up day by day, but the final 14 inches to the situation breaking would be that tidal cycle? So not so much the fundamental cause of the earthquake, but at least leading to a (large?) tendency towards correlated timing? – JeopardyTempest Jan 14 '23 at 09:28
  • @JeopardyTempest Impossible. Whatever tidal energy builds up is quickly lost as heat in the form of geothermal energy, as the crust sinks back to its original position after the tide has passed. The only place where tides can create powerful earthquakes would be Io, where tidal forces from 4 bodies (Jupiter, Ganymede, Callisto, Europa) cause enough stress to trigger these phenomenon. Lunar gravity simply isn't strong enough to cause these stresses. – Alastor Jan 14 '23 at 12:34
  • Thanks, @JohnHoltz. You're right that rigidity is relative as Mr. Grove Karl Gilbert said. In fact the mantle also behaves like a liquid if you wait long enough because of that extreme pressure making it a solid –  Feb 06 '23 at 07:24