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Science

Earth Tides Trigger Earthquakes 43

Posted by michael from the shaky-ground dept.
Dirak writes "UCLA scientists confirmed that Earth tides, produced by the gravitational pull of the moon and the sun on the Earth, causing the ocean's waters to slosh, can trigger earthquakes. There are many mysteries about how earthquakes occur, but now it is clear that it takes about the force arising from changing the sea level by a couple of meters of water to noticeably affect the rate of earthquakes."
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Earth Tides Trigger Earthquakes More

Earth Tides Trigger Earthquakes

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  • "the force arising from changing the sea level by a couple of meters of water"

    can you say "global warming"?

  • This works out (Score:1, Interesting)

    by Dancin_Santa ( 265275 )
    This jives with the latest research that shows that most earthquake activity not related to volcanic activity occurs primarily during full moons.

    A little background is probably necessary to explain that non-sequitor.

    Einstein predicted that energy can have a gravitational field. This is a direct result of his calculations of General Relativity. Photons, though having no mass, have energy called quanta. Each quanta exerts a very small gravitational force due to GR.

    During a full moon, more photons are em

    • Re:This works out (Score:5, Insightful)

      by CheshireCatCO ( 185193 ) on Saturday October 23, 2004 @12:24AM (#10606905) Homepage
      And the net result of those photons's gravitionation affects the Earth not a measurable amount. I don't have a calculator handy, but even the sunlight streaming toward the Earth only has an equivalent mass density of 1E-22 kg/m^3 fight over the surface. You can kind of tell that this isn't important because you never hear about anyone having to account for it. For example, NASA doesn't need to take this into account when plotting spacecraft trajectories. The distance to the Moon, which varies by a few Earth radii (out of an average of 62) is going to affect things a lot more.

      Also, you're theory breaks down when you consider that the Earth gets more additional sunlight when it's closer to the Sun than it does from a full moon. Remember, the Moon is about as reflective as charcoal. Not a lot of light bounces off o it. And what is bounced off (of a smaller surface than Earth has to begin with) is sent off in a lot of directions, not just straight at the Earth.
    • During a full moon, more photons are emitted by the moon (reflected, actually) and thus the moon has a slightly greater gravitational pull during full moons than new moons (where it has very low gravitational force, relatively).

      Wrong. The reason that tides are greater during a full moon is because the gravitational tidal effects of the sun and moon are acting in concert, not due to the extremely negligable effects that photons reflected off the moon have. See the Wiki on Tides [wikipedia.org] for a more detailed expla

    • It is important to note that this this is false. And I mean, Completely Wrong. Not only is the effect completely negligible, the little effect that it has goes in the other direction: the photons from the moon are PUSHING the earth in the other directions, just like if you shoot a bullet a something, it recoils in the other direction. How you could attract something by throwing others things at it is beyond my imagination.

      (For the actual physicists around, yes, I know about gluons and virtual photons. This
    • Ah yes. '+4 Informative', nice one, mooncalf.

    • This is COMPLETELY wrong. The moon's gravity is not a function of its current reflectivity and phase, and has nothing to do with photons. What affects the tides is the relative orientation of the Earth and the moon/sun- whether the water is being pulled all in the same direction by the two bodies, whether there are two pulls at right angles... whether the pulls are working against each other, or in concert... But blaming reflection of photons? That's a whole load of scientific nonsense.
  • I thought it was Sheep's bladders.

  • I kinda thought we already knew this... (Score:3, Interesting)

    by Kanpai ( 713697 ) <[moc.liamg] [ta] [iaWiapnaK]> on Friday October 22, 2004 @10:47PM (#10606524)
    I must've learned in elementary school that earthquakes are caused by shifting plates of rock and earth below us...it seems a natural assumption to say that the power of the tides would have a great effect on moving said plates along. But i guess they needed some scientific proof.

    Can anyone elaborate on my vaugeness, or make sense of what i'm talking about?

    • Plate tectonics has two driving forces - Slab pull, where a descending slab of cold oceanic lithosphere around 100km thick pulls the rest of the crust along, and 'Ridge Push', where the height difference between a Mid ocean ridge and the equlibrium depth of oceanic crust pushes the crust along. Both of these forces are greater than tides by many orders of magnitude.

      Where tides will have the greatest effect is presumably on the shallow angle thrust faults that happen where one place is subducting under an

  • ...a story about effects of el niño on earthquakes within the next 6 months.
  • Sea water weighs about 60lbs. per cubic foot or so, right?

    Considering that the Ocean is a few miles deep, that's obviously a lot of weight to shift around on top of the tectonic plates (which I assume are responsible for Earthquakes).

  • 1971 Sylmar quake (Score:3, Interesting)

    by calidoscope ( 312571 ) on Friday October 22, 2004 @11:30PM (#10606701)
    Time 6AM on the day of a full moon - wondered about the connections between tides and earthquakes since then.

    What most people don't know is that if the shaking lasted maybe 20 seconds longer it could have been the worst natural disaster in US history. The near failure of the Van Norman dam scared the bejeebers out of the Cal Department of Water Resources and they called for a lot of earth fill dams to be rebuilt.

  • Based on this research, it could easily be conjectured that the effect of global warming (which is causing the Polar Ice caps to melt) is also causing Volcanic activity.

    As the Polar Ice caps melt, they add significant volume to [the] Earth(s) Ocean(s). The weight produced by this puts downward force on the tectonic plates. This downward force puts increased pressure on the magma beneath them, and the result is: Earthquakes _AND_ Volcanic activity (ala Mount St. Helens).

  • zerg (Score:4, Funny)

    by Lord Omlette ( 124579 ) on Saturday October 23, 2004 @01:45AM (#10607179) Homepage
    I recommend we ban the tides.

    Don't get me wrong, we will still be able to use the tides if we absolutely had to, I'm not saying that we ever would. I'm talking about banning them from the rest of the world.

  • Other Factors... (Score:4, Interesting)

    by pennsol ( 317791 ) on Saturday October 23, 2004 @02:38AM (#10607383) Homepage
    As a long time resident of the caribbean, I have always noticed that years we have large hurricanes (catigory 4 or 5) the amount of earthquakes in other parts of the world increase. The caribbean inlands sit on a fault line that is connected across Mexico to California and up to Alaska. One of our biggest Hurricanes in recent memory (Hugo in 89, Catigry 5) came 28 days before the big quake in SF. A quick Google search will come up with a few other coincedeces.. The other thing google found is the high amount of quakes in September, when during any given year we have 4 to 7 actve storms in the Atlantic, Caribbean, or Gulf of Mexico. Just a bit more food for thought...
    • Look at Japan, which gets slammed with typhoons(which IIRC, are about the same as hurricanes) and get hit with earthquakes. In fact, pretty much after a month of getting slammed by typhoons, there was a major series of earthquakes [cnn.com] over there. Now granted you always have the coorelation!=causation flaw, but it's really something to look into.
  • I lived in California for a while and survived both the '89 quake in San Fran, and the Northridge quake in LA.

    Both of these quakes were preceded by what the locals all felt was "quake weather", a sort of 'strange heat and cold' combination that just seemed like it was building up pressure over the land. For days before Northridge, we'd been 'feeling like theres gonna be a quake', a sort of perception of the weather system.

    Its interesting to see that tides affect the plates. I wonder if there's more rese
    • Interesting, same weather pattern was reported in Turkey at 1999, just before a 6.8 magnitute earthquake killed around 40 thousand people (officially little over 32 but still more are missing/buried w/o a trace).

    • Both of these quakes were preceded by what the locals all felt was "quake weather", a sort of 'strange heat and cold' combination that just seemed like it was building up pressure over the land.

      Not really. I was closer to the '89 quake than San Francisco was (at Ft. Ord), but we hadn't felt any magic weather around that time. And though I'm a Southern California native my wife, who was standing next to me as it hit, grew up in that area. And again, I'm a California native and have been paying attention

      • There are differences between different individuals' amount of perception to various phenomena. One reason lots of subtle phenomena don't recur in the lab is the brain structure of the experimenters; they're analytical, and their conscious mind is totally ignoring what their gut is telling them, even though they're consciously trying to get it, they don't have the structures in their brains/nervsous systems to do it, no matter how bad they might want to.

      • Well, my experience was different. In LA, my friends, my girlfriend, and I, had been talking about the 'quake weather' for the week before Northridge, and although I'd only been in San Fran for 2 weeks on business before the '89 quake, I still recall thinking 'quake weather' in the days preceding, not after ..

        I lived in LA for 15 years. 'quake weather' was a pretty constant meme in those parts.. but hey, maybe my crowd were more generally paranoid than yours. Could be.

  • R-ALL-OF-T-F-A (Score:4, Interesting)

    by scupper ( 687418 ) * on Saturday October 23, 2004 @05:14AM (#10607779) Homepage
    In California, and in fact in most places in the world, the correlation between earthquakes and tides is considerably smaller, Vidale said. In California, tides may vary the rate of earthquakes at most one or two percent; the overall effect of the tides is smaller, he said, because the faults studied are many miles inland from the coast and the tides are not particularly large.
  • A comment I made just a few hours before this article posted mentioned moving the Moon into a geostationary orbit. This would eliminate lunar tides altogether; only solar tides, which are considerably smaller, would be left. To be sure, two sides of the Earth would experience very high stationary tides for a while (with corresponding low-low-low tides at 90-degree angles), until the Earth itself deformed sufficiently to cancel the effect, which probably wouldn't take more than a couple hundred thousand ye
    • But so much of life relies on the lunar cycle, some directly relying on tides. This would throw the ecosystem completely out of whack. Also, half of the world would experience a somewhat permanent day, light-wise, with the moon being so close to the Earth. Also, the tidal forces themselves would be rediculously stronger -- with the moon more than ten times as close, as would be necessary for geostationary orbit, its gravitational field at the Earth would be over one hundred times as strong. And even if
  • The moon and sun exert tidal forces throughout the earth. Loose water sloshes about some, but the force works on rock, too.

    It should be no surprise, in retrospect, that in places where plates are almost ready to move, a little nudge from tidal forces may induce an earthquake to start.

    The rocks are straining and the sky gives them a little nudge.

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