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Originally posted by KazetNagorraThey are - slightly! - larger. AFAIK the effect is smaller than that of spring and neap tides, but if someone has better figures on that I'm willing to stand corrected.
What is the effect of the moon's relative proximity to Earth on tides?
In any case, what I'd like to know is whether there was a massive earthquake in the same week as this "super moon" last time it occurred, 18 years ago. And one the time previous to that, and all other times. This is, after all, hardly a rare phenomenon, nor is it unexpectedly sudden. One quake is one thing - a scientific hypothesis needs a pattern, if it is to be taken seriously.
Richard
From the wiki link above:
Some studies have reported a weak correlation between lunar activity and shallow, very low intensity earthquakes. However, no evidence has been found of any correlation with major earthquakes.[10][11][12] The 2011 Tōhoku earthquake and tsunami is the only earthquake of 8.0 magnitude or greater to have occurred within 2 weeks of the 14 extreme supermoons from 1900 to the present date,[13][14][15] suggesting that the claim of a supermoon effect on the incidence of large-scale earthquakes is unjustified.
Sounds like it doesn't matter much.
Originally posted by divegeesterYou wouldn't be asking the question if the earthquake hadn't caused a lot of damage and caused a tsunami.
What has when a question is asked got to do with "specialness"? (whatever that means).
Do you have any insight to add to the thread? For example what do you think of the article in the link above?
Yes. My insight is that unless there are any statistics to back up a link, then it is unlikely there is one. There may be a link between earthquakes and tides, but as I already said, it would likely only affect when earthquakes happen, not whether they do or what magnitude they are. Earthquakes happen for a well known reason.
Originally posted by Shallow BlueHere's the earthquake data from 1990 onwards.
They are - slightly! - larger. AFAIK the effect is smaller than that of spring and neap tides, but if someone has better figures on that I'm willing to stand corrected.
In any case, what I'd like to know is whether there was a massive earthquake in the same week as this "super moon" last time it occurred, 18 years ago. And one the time previous to th ...[text shortened]... thing - a scientific hypothesis needs a pattern, if it is to be taken seriously.
Richard
http://earthquake.usgs.gov/earthquakes/eqarchives/year/
Here's the dates of the supermoons
http://en.wikipedia.org/wiki/Supermoon#Dates_of_supermoons_between_1950_and_2050
This is taken from the wiki page -
The 2011 Tōhoku earthquake and tsunami is the only earthquake of 8.0 magnitude or greater to have occurred within 2 weeks of the 14 extreme supermoons from 1900 to the present date.
How about some anecdotal evidence?
Lunar perigee calculator: http://www.fourmilab.ch/earthview/pacalc.html
So we basically want to see if times of perigee-syzygy (great word 🙂) line up with historical big quakes. Some events and what the moon was doing:
Lisbon tsunami, 1 Nov 1755: 3 days before perigee and new moon
Osaka tsunami, 23 Dec 1854: 2 days after perigee, 4 days after new moon
Arica tsunami, 13 Aug 1868: 4 days before perigee, 5 days before new moon
Tokyo earthquake, 18 April 1889: Same day as perigee, 2 days after full moon
Aleutian Islands tsunami, 1 April 1946: 2 days before perigee, 1 before new moon
Aleutian Islands tsunami, 9 March 1957: 5 days before perigee, 8 days after new moon
Kamchatka tsunami, 4 Nov 1952: 6 days after perigee, 3 days after full moon
Chile tsunami, 22 May 1960: 10 days after perigee, 3 days before new moon
Banda Aceh tsunami, 24 Dec 2004: 3 days before apogee, 2 days before full moon
By the way the Japanese earthquake happened on 11 March, 8 days before perigee, so therefore a super moon couldn't have had anything to do with it.
For info, the tidal force of the moon on the earth is proportional to (1/r^3). Mean moon distance (r) is 384 400km, perigee can be 357 000km, which means the tidal force of the moon is 25% greater than the mean during perigee.
The change in gravitational field due to a super-moon really isn't very big. While there may act as a trigger event and affect the timing of the quake, the magnitude of the earthquake depends on the stored energy between the plates, which is accumulated slowly. The island changed position by a few metres, this is a lot of built up strain. The super-moon just can't have contributed that much extra energy.
Originally posted by ElleEffSeeeTo put these in perspective, a new moon or full moon exists every 14 days or so. So every day of the month is no greater than 7 days away from one of them. (Do I have that right?)
Lisbon tsunami, 1 Nov 1755: 3 days before perigee and new moon
Osaka tsunami, 23 Dec 1854: 2 days after perigee, 4 days after new moon
Arica tsunami, 13 Aug 1868: 4 days before perigee, 5 days before new moon
Tokyo earthquake, 18 April 1889: Same day as perigee, 2 days after full moon
Aleutian Islands tsunami, 1 April 1946: 2 days before perigee, 1 b ...[text shortened]... new moon
Banda Aceh tsunami, 24 Dec 2004: 3 days before apogee, 2 days before full moon
So the numbers given (3, 4, 5, 2, 1, 8, 3, 3, 2) seem to be a fairly normal random distribution over the 7 possible numbers. (I don't know how that 8 got in there 🙂 )
Though it is interesting that there are no zeros, it is not really surprising considering the small sample.
Originally posted by twhiteheadYep the lunar month is 29.5 days so new or full moon every 14.75 days. Remember though that we're not just interested in sun-moon-earth syzygy but also that the moon is at perigee, so the joint distribution of the time of lunar month and the time of perigee-apogee period (27.5 days) should be considered.
To put these in perspective, a new moon or full moon exists every 14 days or so. So every day of the month is no greater than 7 days away from one of them. (Do I have that right?)
So the numbers given (3, 4, 5, 2, 1, 8, 3, 3, 2) seem to be a fairly normal random distribution over the 7 possible numbers. (I don't know how that 8 got in there 🙂 )
Though ...[text shortened]... interesting that there are no zeros, it is not really surprising considering the small sample.
Originally posted by ElleEffSeeeI notice that nearly every event in your list includes a tsunami. Why is that? Tsunamis are not always caused by big quakes (in fact they are quite rare as far as I know).
So we basically want to see if times of perigee-syzygy (great word 🙂) line up with historical big quakes.
So your list is really a subset of all big quakes and doesn't include many of the biggest.
So are the quakes in question hand picked to try and make a link, or is there an argument for linking tsunamis in particular with the movement of the moon (which would be hard to explain)?
I think everyone should know the basic stats:
http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php
Earthquake Facts and Statistics
Frequency of Occurrence of Earthquakes
Magnitude Average Annually
8 and higher 1 ¹
7 - 7.9 15 ¹
6 - 6.9 134 ²
5 - 5.9 1319 ²
So if we are discussing >7 magnitude quakes, we average one every month, so we should statistically expect to find a lot more near perigee than in the given list.
I'm not a statistician, but let me have a go: the following is for >7 magnitude quakes only
average no per day: 0.04
average no within 5 days of an apogee or perigee: 0.5
no of apogees and perigrees since 1755 : 3400
no expected on an apogee or perigree since 1755 : 150
no listed in ElleEffSeee's post on an apogee or perigree: 1
So either he is restricting himself only to larger quakes, or those that cause tsunamis, or quakes avoid those apogess and perigees like the plague!