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Here, in New Zealand, we just had a 7.5 magnitude earthquake hit. Alot of people are saying that the super moon caused this.
I have doubts as to the super moon actually 'causing' it but could have it contributed to the earthquake due to its stronger gravitational pull?
The forces involved in the New Zealand earthquake are not amenable to precise evaluation - at least not without detailed geotechnical evaluation, but we can use the peak ground acceleration as a proxy. For a magnitude 7.5 earthquake the peak ground acceleration is about 0.4g. Compare this to the normal moon's gravitational acceleration on Earth's surface of about 3.318 E-5 g. 'Super-moons' are about 16000 km closer than usual, yielding a gravitational acceleration of 3.783 E-5 g. Therefore the differential gravitational acceleration of a super-moon, compared to a normal moon, is about 4.65 E-6 g. Or to put it another way, the effect of a super-moon is to create about a 0.001% of the acceleration (and hence force) required for the accumulated strain energy to overcome friction, and hence cause the earthquake. This assumes that all of the moon's gravity was aligned in such a way as to exacerbate strain along the slip plane - which is never going to be the case.
I suppose that one could argue that the miniscule gravitational force of a super-moon could have been the 'straw that broke the camel's back', but the accumulated strain energy in the ground must have been so great that the earthquake was about to happen anyway, with or without the moon's gravity.
Afterthought: With the boot on the other foot: The Earth's much larger gravitation has an effect on the Moon. There are moon tides which cause regular, small but measurable moon-quakes. See Moritz and Melchior (2013), Tidal Interactions in the Earth-Moon System.
Keep in mind that this "special" "supermoon" is only about 0.5% closer this month than it was last month, or will be next month. And now is only 0.1% closer away at last year's minimum (and in fact, the minimum distance each year of the past 20 is only separated by 0.3% variation)
Makes it a little less exciting, eh? [source for data: timeanddate.com]
And likewise this article from space.com suggests that tide differences between a supermoon and a typical full moon are likely fairly small.
I'm certainly no expert on any of these topics in question, and am hopeful we'll see more precise calculations and details from someone more plugged into these fields. But that information at least suggests that it is dubious to credit the earthquakes to the exceptional proximity of THIS particular "supermoon".
Now do supermoons, or for that matter, full moons in general, cause earthquakes? I have no expertise in any of these topics areas (you can see that with my related question that I happened to post earlier this week asking about seasonal\temperature influences). But I decided to do a quick rough study because it was an interesting question that I had as well.
Applying the EMSC-CSEM earthquake search, I found that 7.9 and greater magnitude quakes gave me a good manageable set to work with from their database (dating to October 2004). I did not look at potential results when choosing the set size. But found it was a fair size to put together, and would at least give a potential taste.
So here are all >= 7.9s in the past 12ish years, as well as their moon phase and earth-moon distance (which appears to vary from about 356500-407000 km, completing 1-2 cycles a year):
Breaking it down (after removing the Japan aftershock), seems a bit of a predilection for full moons:
(6 of the 19 were 90+% full).
And just maybe a slight increase near new moon as well, which would match the way that earlier article described that tides work:
(5 of 19 <= 12%).
Here's a histogram of the spread [made at wessa.net]:
But it doesn't seem there's as much of a trend in distances:
It's almost certainly not enough data to draw a rock solid conclusion, but interesting that it seems hints at favoring full moons. I'm not sure what statistical calculations to do to prove it... the mean is only 51%, so it'd need more than just a mean test to prove that it's bi-modal (favoring full/new moons).
But this quick look certainly seems to suggest at least that there isn't obvious trends in earth-moon distance impacting earthquakes (R^2 = 0.14).
The real connections may be much more complex (varying by location\geology, only affecting certain types of earthquakes, more significant for weaker earthquakes, etc). But hopefully this try using big data from about the last decade is at least a help!
Hope the cleanup goes well AnonDCX!
