On the 14th of November 2016, the moon is both full, and is on its closest approach to Earth, causing its largest appearance size until 2033. Citation This large appearance gives it the 'super-moon' name.

On the 13th of November 2016, New Zealand suffered a major earthquake, with a magnitude of 7.8, as well as an accompanying tsunami. BBC Link about Earthquake

Currently, a post is going around on Facebook, with someone predicting this earthquake, claiming that the supermoon is the cause of this, due to an increased gravitational pull from the moon.

It is known that the moon's gravitational pull does have an affect on the earth, as seen by tidal behaviour, but is this pull enough to cause an earthquake and tsunami, or is this behaviour purely coincidental?

From https://www.facebook.com/groups/1680211292261330/permalink/1817053615243763/,

Heads Up: On 14th November and a couple of days either side of that date, watch for a major earthquake, and quite possible in South Pacific area. The reason for this is that 14th of Nov will be a "super moon" largest for this century (ie. moon closest to Earth on this date than it has been for a long time). This means it will be a period of increased gravitational pull from the moon. There was a recent large earthquake in Italy and as when one plate shifts it places stress on other plates, the chances of a big quake are higher for something down this end of the globe. Also geo-engineering is more likely to have success during this time and can be targeted on a specific area.

This is just a possibility, but be alert, that is all I am saying. Always be prepared with water supplies and even food supplies as is possible. Rice is a good food supply item because it lasts a long time and will keep people fed....and is relatively cheap.

It can be bought in 5 or 10kg bags from a supermarket for usually $10 to $20. Stay safe.

  • I've specified that the claim is about a measurable effect, otherwise the answer is trivially "yes" since gravitational force varies by distance. – Sklivvz Nov 14 '16 at 1:04
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    Note that the moon comes to perigee once per lunar month, and so a tidal triggering effect could be expected to show up in correlation with the lunar cycle. The tidal effect of the sun is roughly half the size of that due to the moon, and the two effects add when the moon is near new or full phase (and partially cancel when the moon is near a quarter phase), so while supermoons have the distinction of the maximal lunar effect combined with the solar effect, they are not alone in that distinction: lunar perigees that occur in coincidence with new moons generate the same size effect. – dmckee Nov 14 '16 at 2:54
  • Isn't it possible to edit Facebook posts after they're made? Are you certain that the post in question predicted an earthquake before the earthquake actually happened? – Gareth McCaughan Nov 14 '16 at 17:29
  • Can Astronomical Tidal Forces Trigger Earthquakes? "The gravitational pull of the sun and moon is far too weak to trigger an earthquake on its own. When seawater accumulates above submarine faults that are already close to rupture, however, the increased pressure can reduce friction on the fault and thereby hasten a quake’s onset." – Keith McClary Feb 16 '17 at 2:58

To first order, no, supermoons don't have measurable effects on earthquakes.

They might have a very very small effect on small earthquakes.

It isn't a ridiculous question. The strength of tidal forces is related to distance - tidal acceleration scales as roughly the inverse cube of distance. Wikipedia has the textbook derivation if you are curious.

Phil Plait at the Bad Astronomer blog points out that if you combine a spring tide (when Earth-Sun-Moon are in a straight line) with the moon being very close, you can get tides that are 50% stronger than normal.

But of course, having stronger tides doesn't mean that you must have more earthquakes (or more volcanic eruptions). Groups like the USGS have looked at earthquake frequency vs tides, and come to the conclusion that any effect is nonexistent, or at best very tiny.

According to John Vidale, a seismologist at the University of Washington in Seattle and director of the Pacific Northwest Seismic Network:

"Both the moon and sun do stress the Earth a tiny bit, and when we look hard we can see a very small increase in tectonic activity when they're aligned...you see a less-than-1-percent increase in earthquake activity, and a slightly higher response in volcanoes ."

From livescience.

The same page quotes William Wilcock (also from the University of Washington) as saying he sees greater earthquake activity in subduction zones at low tide, but he sees no more activity during new and full moons.

Finally from the same source, quoting John Bellini, a geophysicist at the U.S. Geological Survey:

A lot of studies have been done on this kind of thing by USGS scientists and others. They haven't found anything significant at all.

Just recently, researchers in Japan were able to use existing data of earthquakes and the lunar phases to show a relationship between tidal stress and probability of large earthquakes.

From the excerpt, published in Nature Geoscience: Earthquake potential revealed by tidal influence on earthquake size–frequency statistics

Here we calculate the tidal stress history, and specifically the amplitude of tidal stress, on a fault plane in the two weeks before large earthquakes globally, based on data from the global, Japanese, and Californian earthquake catalogues. We find that very large earthquakes, including the 2004 Sumatran, 2010 Maule earthquake in Chile and the 2011 Tohoku-Oki earthquake in Japan, tend to occur near the time of maximum tidal stress amplitude. This tendency is not obvious for small earthquakes. However, we also find that the fraction of large earthquakes increases (the b-value of the Gutenberg–Richter relation decreases) as the amplitude of tidal shear stress increases. The relationship is also reasonable, considering the well-known relationship between stress and the b-value. This suggests that the probability of a tiny rock failure expanding to a gigantic rupture increases with increasing tidal stress levels. We conclude that large earthquakes are more probable during periods of high tidal stress.

So basically, yes, the moon can cause big earthquakes on earth, or make small earthquakes bigger. And the effect is measurable. They are not mentioning "super-moon" phases there, and I don't have access to the paper. Since the pull is strongest in this phase, I think it's safe to say that the probability of large earthquakes is higher than usual at this time. This is how I interpret the excerpt. Also, I'm not a Geoscientist.

Why is the moon's pull strongest the closer it comes to earth? Because the gravitational force between two objects is a formula of their masses and the distance between them.

F = G * M * m / R ^ 2

R is the distance between the objects. If they get closer to each other, R decreases. When the denominator decreases, the resulting Force increases.

I found an online tool that calculates the gravitational force: Newton Law of Gravity Calculation

I actually put the numbers in to see what the difference in force really is between the Apogee (furthest distance between moon and earth) and Perigee (closest distance).

The gravitational force is 30% stronger at Perigee than at Apogee. Type in the values and test it yourself.

The Japanese researchers figured out that large earthquake probability is higher when the moon causes maximum "tidal stress". When is this tidal stress the strongest? When the moon pulls strongest. There will be less tidal stress on the side of earth where the moon doesn't pull and more tidal stress on the side of earth that faces the moon. At least this is the only way that makes sense to me.

By the way, today, the 14/11/2016 is the Perigee of this year.

The central argument of this answer is theoretical in nature. We do not allow answers based uniquely on common sense or pure logic. Answers which are wholly based on a theoretical model are generally downvoted and may be deleted. See FAQ: What are theoretical answers?

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    they nowhere in your quote state that the moon causes earthquakes, only that high tidal stresses (which, though unstated, can be in part attributed to the moon) can cause fractures in fault lines, which in turn can lead to large earthquakes. So at most we can come to the working hypothesis that a full moon may be a factor in the triggering of earthquakes. That the moon is the sole factor in such I can't conclude from what you quote here. – jwenting Nov 14 '16 at 7:57
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    "Since the pull is strongest in this phase" = please show this is true, and moreso that the probability during a supermoon increases a lot above the background noise level. After all, the claim is that the risk increases enough to justify purchasing bulk water and rice. – Oddthinking Nov 14 '16 at 14:37
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    @Oddthinking I added more details to the answer. I doubt though that the additional risk should make people start hoarding of water and rice. If you live in Christchurch or other areas where earthquakes occur regularly, you certainly prepare for a disaster anyway. – daraos Nov 14 '16 at 19:20
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    Tidal force varies as the inverse cube of the distance. It is not caused directly by the gravitational pull of the other body, but by the difference in gravitational pull at different points. That is, the nearer parts of the earth are subjected to a stronger gravitational pull from the moon than are the farther parts, and this creates the internal stress. – phoog Feb 13 '17 at 14:30
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    @phoog's comment is correct. The size of the lunar acceleration itself is utterly irrelevant. It is only the change over the body of the Earth that matter. To mention a relevant example, the magnitude of the force on the Earth due to the sun is many times that of the Moon on the Earth, but the lunar tides are stronger than the solar ones. As long as you have that error in this answer it is woefully misleading. – dmckee Mar 15 '17 at 20:53

No, and the answer to that question is actually a lot easier than the other explanations here.

The fact of the matter is that a "Supermoon" is simply the coincidence of the full moon, and the moon's perigee - the closest approach of the moon -in its orbit. The moon reaches perigee every single orbit, so the tidal stresses on the crust of the earth would be about equal to every other time this happens. Moreover, the full moon is when the moon is opposite the sun, not on the same side of the Earth as the sun. If anything, this has the effect of cancelling out some of the gravitational force of the moon on the Earth. The time when the moon is new and at its perigee at the same time would have the greatest tidal force on the Earth. But that doesn't look anywhere near as pretty except during an eclipse.

Also, you need to keep in mind that the force of gravity from the moon is really tiny. About 0.0000001 meters/second^2. The fact that we notice it at all in the tidal effect is because that force is spread out over the really large area of our oceans, and is different depending on which side of the Earth you're on.

The supermoon has no special effect on the Earth except looking 10% bigger and providing some better astronomical images for craters near the edge of the moon at that time.

The central argument of this answer is theoretical in nature. We do not allow answers based uniquely on common sense or pure logic. Answers which are wholly based on a theoretical model are generally downvoted and may be deleted. See FAQ: What are theoretical answers?

  • This answer is entirely theoretical and therefore inappropriate for this site. The theoretical answer is also not very compelling. For example, the tidal force due to to the Earth/Moon/Sun alignment that you discuss can be 50% stronger. It is not entirely unreasonable to suggest that applying that effect over a few ocean's worth of water would do something to earthquake frequency. Hence the need for data. – KAI May 17 '17 at 20:55
  • You're right. Skeptics is completely useless for actually finding answers. I could link to "research" done by the Daily Star and have an answer accepted, but do the math? Pff. Give me a break. Skeptics doesn't want math! – Ernie May 24 '17 at 17:14

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