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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.

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    $\begingroup$ 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. ... $\endgroup$
    – Fred
    Commented Jan 12, 2023 at 1:43
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    $\begingroup$ ... 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. $\endgroup$
    – Fred
    Commented Jan 12, 2023 at 1:51
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    $\begingroup$ 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. $\endgroup$
    – user28185
    Commented Jan 12, 2023 at 10:52
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    $\begingroup$ Source: USGS $\endgroup$
    – user28185
    Commented Jan 12, 2023 at 10:52
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    $\begingroup$ Thanks, @Universal_learner $\endgroup$
    – user27902
    Commented Jan 12, 2023 at 14:33

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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.

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  • $\begingroup$ Thanks a lot!.. $\endgroup$
    – user27902
    Commented Jan 12, 2023 at 14:31
  • $\begingroup$ So at Periapsis, What Richter scale Earthquake would it be? $\endgroup$
    – user27902
    Commented Jan 12, 2023 at 15:04
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    $\begingroup$ 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 science.howstuffworks.com/environmental/earth/geology/… $\endgroup$
    – JohnHoltz
    Commented Jan 12, 2023 at 15:30
  • $\begingroup$ 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? $\endgroup$
    – user27902
    Commented Jan 12, 2023 at 15:36
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    $\begingroup$ 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. $\endgroup$
    – mmesser314
    Commented Jan 12, 2023 at 22:07

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