Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: norcalclimber on 26/05/2010 02:35:52
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So we know that the gravitational pull of the Sun and Moon gives us our high and low tides, right? And we get our highest tides when we have a total solar eclipse, presumably because their gravitational fields are lined up.
But what about tectonic plates?
When the gravitational fields are concentrated over a specific region, could it trigger a tectonic shift/earthquake?
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I think the slight elliptic orbits of the earth around the sun and the moon around the earth would have a greater effect that the precise alignment but I take your point, in general, that tidal effects could help to trigger earthquakes. Generally the tidal effects are maximum at a new moon (an eclipse being a precise alignment) and a full moon. It is an interesting and testable hypothesis and it would be interesting to see if there is any correlation.
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There have been many attempts to test whether the Moon passing between the Earth and the Sun during a eclipse has any gravitational shielding effect but it is difficult to separate this from the thermal effects caused by shielding the Sunlight and no proven effect has been shown as yet.
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Norcal / Graham - it is easy to download earthquake incidence data. If you fancy some number crunching to see if the theory is correct - I will download as much as can be found and find some way of randomising to create a blind. I think I can get all earthquakes recorded since 1973 with day, time(hh:mm:ss:00), lat and long to 2 decimal places, depth, and magnitude. FYG there were 1372 in Jan 2010; so there is a fairly substantial data base. I dont have the scientific background or experience to create a test, but I'll do any dogsbody work required. Matthew
Edit - just seen syhprum's - Oh Well! its been done. Still up for a bit of homemade testing if anyone else is.
And can we really find influence on tectonics movements of 7 mins of shade?
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Thanks Matthew, but I will leave it to Norcal I think. It's interesting, but not THAT interesting :-)
Syphrum, this has nothing to do with gravitational shielding (which I think is complete nonsense anyway) - at least I don't think this is what Norcal was suggesting - but just the maximum tidal force conditions.
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If you think of gravity as a distortion of what would nominally be flat space-time, then changes of gravity due to the alignment of Luna and Sol will not induce Earthquakes because the distorted regions of space-time won't be aware of the distortion unless there is a significant gravitational gradient across the region.
For example, a very small space probe, closely orbiting a neutron star wouldn't experience a lot of stress because there would be very little difference in the gravity across its tiny diameter, but a large probe in the same close orbit would be pulled apart because there would be a significant difference in the forces acting across its greater diameter.
Because the distance between the Earth and Moon, let alone the Sun, is very great compared with the diameter of the Earth there is relatively little difference in the forces acting across the diameter of the Earth, and so consequently there'll be very little induced stress.
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Lee, the gravitational gradient is called a tidal effect for good reason - the clue is in the name. It is sufficient to move billions of tons of water up and down so I would not like to say it has no effect on the earth's crust at all. The effect of alignment (or being on opposite sides) creates a spring tide so there is a definite, significant and large effect at the surface of the earth. I don't think it plays a major factor but there may well be some correlation. Geological changes are generally on a long timescale so you might see the trigger for an event being when something causes the change to a tipping point. I would not rule out a correlation. There is an offer from Matthew if you want to prove this wrong :-)
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Thanks all, I would love to do some number crunching to see if there is any correlation(doubt I'm qualified). I'm thinking it would probably only trigger an earthquake, not cause though, so that might make it rather difficult to correlate. You are correct graham, I'm not talking about gravitational shielding, rather the aligning of both the sun and moon's gravitational fields. It seems there must be at least some effect on the tectonic plates, because as graham pointed out it is sufficient to move billions of gallons of water. We do have a solar eclipse coming up soon, and it will be visible over the south pacific, which is a relatively active plate...
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As the Moon orbits the Earth it raises a tide on the the ocean and to a smaller extent on the crust as you agree with me that there is no gravitational shielding how can its few minutes between the Sun and the Earth have much additional effect other than thermal.
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While the gravitational fields are only lined up for a few minutes, they are moving across the tectonic plates for far longer. Plus, the fields produced are rather large, so shouldn't it work similar to psi(e.g. 1lb per square inch over 100 million square inches could lift 100 million lbs)? The amount of pull is shifting continuously too, isn't it? Couldn't earthquakes be described similar to ocean waves? Energy moving through the earth's crust, as compared to energy moving through the ocean?
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graham.d - I've never heard a gravitational gradient referred to as the tidal effect and as I understand it the tidal effect is not due to the gravitational gradient across a region of space but just due to the direction of the gravitational vector, which is why we get high tides at both sides of the planet, along the vector axis. If the tidal effect was due to the gravitational gradient i.e. the difference in the strength of the gravitational force across a region then we'd only have one tide per day instead of two.
Our tides are primarily due to the Moon, at an average distance of around 384400 km away from the Earth, which has an equatorial diameter of 6378 km; how much of a gradient is there going to be across the diameter of the Earth from something that's 60 times that distance away from us? Spring tides only highlight this, with Sol being about 150000000 km away from Earth i.e. over 25000 times the Earth's diameter. The gravitational gradient across the diameter of the Earth, due to the Moon and the Sun, is negligible.
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Yes, Lee, you are quite right. I should think before I post :-) Nonetheless, I don't understand why you don't think that the force that ripples around the earth every 12 hours would not have any effect on the land when it does so on the oceans. It is the same forces, admittedly to a much larger amount, that create all of the volcanos and internal heating on Jupiter moon, Io. As I said earlier, I don't think the effect will be very large, but it seems likely that it could have some effect so that the triggering of an event may be correlated with a time of maximum stress.
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I don't think the effect will be very large ...
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http://en.wikipedia.org/wiki/Earth_tide#Tidal_constituents
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Nonetheless, I don't understand why you don't think that the force that ripples around the earth every 12 hours would not have any effect on the land when it does so on the oceans.
Actually, I do think you've got a good point there, but it's still not entirely clear to me yet. I think I need to think about it a bit more (actually, actively 'thinking' about it is a bit of a misnomer as I find that not thinking about some problems for a while, and then coming back to them after a break, can get me out of a wrong groove and let me look at them afresh, and in the mean time my subconscious often seems to have worked stuff out on its own too - Heh - it's a bit like leaving something to simmer away while I go off and do something else until it's finished cooking)
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Yes, the NOT thinking thing works for me too. I suspect it must be quite common. I can be thinking of a problem for days then just forget it and then find I wake up one morning and my brain has thought it through in my sleep.
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http://en.wikipedia.org/wiki/Earth_tide#Tidal_constituents
Well, I guess there has been some major studying of the subject already, thanks RD [:)]
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There are actually a number of studies which suggest that a few areas may have lunar induced earthquakes. I should be able to find at least some of them.
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Here is the first link I located:
http://www.aolnews.com/weird-news/article/do-moon-phases-cause-earthquakes/19445950 (http://www.aolnews.com/weird-news/article/do-moon-phases-cause-earthquakes/19445950)
Tom Jordan, a USC professor and director of the Southern California Earthquake Center, says that while some studies indicate tidal effects may have an effect on smaller quakes, there's no evidence they have an effect on bigger quakes like the one April 4 centered in Baja California.
More follow up here
http://www.unknowncountry.com/news/?id=2069 (http://www.unknowncountry.com/news/?id=2069)
Author David Nabhan thinks a quake could be caused by a lining up of the moon, sun and Earth and says most large earthquakes happen when the moon is full. But Lucy Jones, of the U.S. Geological Survey, says, "There has never been any demonstrated correlations of large earthquakes with the full moon?If doing the easy things like the full moon worked, we would be doing it."
Jim Berkland, a San Jose geologist, predicted the 1989 quake five days before it happened in an article in his local newspaper. He claims to have 75% accuracy at predicting major quakes by consulting the planetary alignments?as well as the Lost and Found section of the newspaper, to figure out how many dogs and cats have run away from home. He also consults the geyser at Calistoga, California, to find out if its regular eruptions have been interrupted.
I did find this article from Science, a AAAS publication
http://www.sciencemag.org/cgi/content/abstract/306/5699/1164 (http://www.sciencemag.org/cgi/content/abstract/306/5699/1164)
Earth Tides Can Trigger Shallow Thrust Fault Earthquakes
We show a correlation between the occurrence of shallow thrust earthquakes and the occurrence of the strongest tides. The rate of earthquakes varies from the background rate by a factor of 3 with the tidal stress. The highest correlation is found when we assume a coefficient of friction of µ = 0.4 for the crust, although we see good correlation for µ between 0.2 and 0.6. Our results quantify the effect of applied stress on earthquake triggering, a key factor in understanding earthquake nucleation and cascades whereby one earthquake triggers others.
I hope this is helpful.
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Here is the first link I located:
http://www.aolnews.com/weird-news/article/do-moon-phases-cause-earthquakes/19445950 (http://www.aolnews.com/weird-news/article/do-moon-phases-cause-earthquakes/19445950)
Tom Jordan, a USC professor and director of the Southern California Earthquake Center, says that while some studies indicate tidal effects may have an effect on smaller quakes, there's no evidence they have an effect on bigger quakes like the one April 4 centered in Baja California.
More follow up here
http://www.unknowncountry.com/news/?id=2069 (http://www.unknowncountry.com/news/?id=2069)
Author David Nabhan thinks a quake could be caused by a lining up of the moon, sun and Earth and says most large earthquakes happen when the moon is full. But Lucy Jones, of the U.S. Geological Survey, says, "There has never been any demonstrated correlations of large earthquakes with the full moon?If doing the easy things like the full moon worked, we would be doing it."
Jim Berkland, a San Jose geologist, predicted the 1989 quake five days before it happened in an article in his local newspaper. He claims to have 75% accuracy at predicting major quakes by consulting the planetary alignments?as well as the Lost and Found section of the newspaper, to figure out how many dogs and cats have run away from home. He also consults the geyser at Calistoga, California, to find out if its regular eruptions have been interrupted.
I did find this article from Science, a AAAS publication
http://www.sciencemag.org/cgi/content/abstract/306/5699/1164 (http://www.sciencemag.org/cgi/content/abstract/306/5699/1164)
Earth Tides Can Trigger Shallow Thrust Fault Earthquakes
We show a correlation between the occurrence of shallow thrust earthquakes and the occurrence of the strongest tides. The rate of earthquakes varies from the background rate by a factor of 3 with the tidal stress. The highest correlation is found when we assume a coefficient of friction of µ = 0.4 for the crust, although we see good correlation for µ between 0.2 and 0.6. Our results quantify the effect of applied stress on earthquake triggering, a key factor in understanding earthquake nucleation and cascades whereby one earthquake triggers others.
I hope this is helpful.
Thank you! That was extremely helpful. I thought I heard somewhere that Jupiter could be lined up with the sun and moon for this upcoming solar eclipse? I have no idea whether this is true or not, and since I am extremely new to looking up planetary alignments and such, I still haven't found a very good place to find this information out.
Any suggestions on good websites to look up planetary/moon/sun alignments?
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I think it is stretching it (ho ho) a bit to think that alignment of planets has any effect; I think this is really too small an effect to be significant. The work that suggests there may be correlation with tides in certain circumstances for smaller earthquakes seems the most believable and the research appears to be carried out scientifically.
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Lol, I am sure you are correct that alignment of the planets is a bit of a stretch.
I know correlation is not causation, and coincidences happen... but it is a bit interesting to me that the recent earthquake in Haiti happened 2 days before an eclipse, when the gravitational fields of the Sun and Moon were almost fully lined up.
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We have to be careful about seeing coincidences as patterns. You might want to check out Stellarium. It is a free program that can display the night sky. It seems to be quite good.
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the effective diameter of the Sun is about 0.5 degree if we exclude gravitational shielding that I think we all do there can be very little difference in the gravitational field on the Earth when it passes 0.26 degree below the centre of the Sun (no eclipse) and when it passes right across the face of the Sun (total eclipse).
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the effective diameter of the Sun is about 0.5 degree if we exclude gravitational shielding
gravitational shielding what's that - I thought that concept was highly disputed and more at home in sci-fi.
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" if we exclude gravitational shielding that I think we all do "
I think that it is well proven that gravitational shielding cannot exist I only mention it to state that is the only thing that could cause earthquake's during an eclipse.
If gravity is mediated by Gravitons they must be incredibly light, I have seen it suggested that they are 10-^10 the mass of Neutrinos and it takes light of lead to stop them !.
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the effective diameter of the Sun is about 0.5 degree if we exclude gravitational shielding that I think we all do there can be very little difference in the gravitational field on the Earth when it passes 0.26 degree below the centre of the Sun (no eclipse) and when it passes right across the face of the Sun (total eclipse).
Actually, I think we can all agree that there is plenty of difference between an eclipse and no eclipse...since we get our highest tides when we have a solar eclipse, there is absolutely no doubt that there is a significant difference in the force felt by Earth's crust. Unless perhaps I received poor information on when we have our highest tides?
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I think you may have poor info norcalclimber. Spring tides (the highest and the lowest) occur every 2 weeks when the moon is on the same side as the sun and again when the moon is on the opposite side from the sun. An eclipse only affects a small area of the earth's surface and the difference of the force produced when the alignment is so exact from when it is not is very small indeed, though possibly not totally negligible. The biggest effect will be due to the eliptic nature of the moon's orbit and the biggest tides arise when the moon is closest.
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I think you may have poor info norcalclimber. Spring tides (the highest and the lowest) occur every 2 weeks when the moon is on the same side as the sun and again when the moon is on the opposite side from the sun. An eclipse only affects a small area of the earth's surface and the difference of the force produced when the alignment is so exact from when it is not is very small indeed, though possibly not totally negligible. The biggest effect will be due to the eliptic nature of the moon's orbit and the biggest tides arise when the moon is closest.
It is very possible my info/understanding is poor, as in this case it comes from watching some program(don't remember which) on Discovery channel/or Science channel. I was aware that spring tides are highest, but I feel certain the program I watched also stated that tides during Total Solar eclipses are even higher than spring tides? I completely agree with you regarding the biggest effect being when the moon is closer, and during a total solar eclipse the moon is closer than during other eclipses as well as having the added benefit of the Suns gravitational field lined up. I still think the effect could be quite large from them being lined up, going back to the p.s.i. example; even a very small p.s.i. over a large area is significant, and in the case of an eclipse it seems to me that if it is focused over a hot spot it may be easily enough of a difference to be the proverbial straw which broke the camels back.
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Ah yes, science programs of TV. Sadly, their desire to overdramatise things sometimes gets in the way of accuracy, even to the extent of becoming misleading at best, and sometimes just getting it plain wrong.
Lol - I was just going to give an example of such a mistake that I saw in one of these programs, and was going to post the Wikipedia link for the real meaning only to find that Wikipedia has currently got it wrong too - oops [;D]
The example I was going to give concerned a phenomenon known as the Iron Catastrophe. According to this particular TV science program (and Wikipedia too) the term Iron Catastrophe refers to the migration of iron down towards the core of the Earth when the planet was still molten, which is really not much of a catastrophe, seeing as it caused no problems for anyone or anything and it didn't happen with sudden rapidity; catastrophe just isn't the right word to describe it.
In fact, the term more correctly refers to the point in a nova when all of the elements lighter than iron have been fused and the sudden and catastrophic collapse of the star occurs. Up to the point of the Iron Catastrophe, the fusion of the elements lighter than iron still releases sufficient energy to prevent the collapse of the star against its own gravity. Fusion of iron though, requires energy, so when the star starts fusing iron at its core it also starts sapping the energy preventing its collapse due to gravity. As a result, the final collapse of the star is both very quick, and from the star's point of view, most certainly catastrophic.