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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 --- ex-moderator kitten 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
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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.

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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.

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  • 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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