
Gravitational pull 'has role in quakes' - adanto6840
http://www.bbc.com/news/science-environment-37350839
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lutusp
Quote: "When the tug of gravity is strongest, they added, "the probability of
a tiny rock failure expanding to a gigantic rupture increases"."

The article's author clearly didn't understand the original paper. It's not
gravitational force that was being examined, but its first derivative --
changes in gravitational force from one location to another and/or one time to
another, i.e. tidal stresses.

In fact, any change in gravitational force -- either an increase or a decrease
-- could produce the effects being examined. So it's not the strength of the
gravitational force, but the fact that it changes over time, and from one
location to another.

Consider Jupiter's moon Io as a classic example. If Io were in a circular
orbit, it would be a cold, dead world. But Io's orbit is elliptical, which
causes perpetual changes in tidal force (the first derivative of gravitational
force) across Io's diameter. The result is a very highly seismically and
volcanically active body.

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laretluval
Without gravity, there would not be very many earthquakes.

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givinguflac
Or planets lol.

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M_Grey
Plus no stars and any large scale formation, totally diffuse dark matter, and
only the heavy elements from very early nucleosynthesis, assuming you could
have a BB without gravity. Practically though, it's hard to imagine spacetime
that has no curvature at all beyond a local IF.

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Retric
This is kind of old news, I found references in late 1990's to tides
influencing earthquakes around volcanos while doing a high school science
project. The problem is the effect size is tiny. I thought it was a cool
project, but someone else at that science fair did the same thing. I suspect a
lot of people have looked into it over the years.

PS: USGS has a great database if earthquake data going back decades, it was
downloadable as a ~100 meg txt file. Just remember there is a lot of different
kinds of faults, and volcanos cause a lot of earthquakes. Modern version looks
rate limited to 20,000 events though.

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crygin
There's some research out there that correlates certain types of marine quakes
with tidal levels:
[http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.2009....](http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.2009.04319.x/abstract)

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ISL
For those reading the article (it was free to read for me at home), it looks
like their central point is shown in Figure 2a. Mind the vertical axis as you
look across Figure 2.

The statistics are thankfully low for strong earthquakes, but another century
or so will provide an ample test of their hypothesis.

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th0ma5
I looked up the San Francisco 1989 earthquake and it was 2 days past a full
moon. I tried to look up tide data, which is out there, but I'm on my phone
and didn't want to bother with ftp or CSV stuff, heh. Probably just a
coincidence but was interesting to me at least.

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GFK_of_xmaspast
Roughly half of all earthquakes are within one week of a full moon.

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ProAm
I dont believe the phase of the moon as anything to do with the earthquakes,
more the orbital position...

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ceejayoz
Psst. The moon takes about four weeks to go from full moon to full moon, so
"within a week of full moon" is roughly 50% of all days - earthquakes or
otherwise.

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foobarian
I'm pretty sure OP was joking. Except what if the quakes are not evenly
distributed? Then the joke is wrong :-)

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Florin_Andrei
It is a joke - but intuitively you'd expect some correlation between tides and
earthquakes. It would be somewhat surprising if such correlation did not
exist, and then I'd wonder what does that mean for the mechanisms that produce
EQs.

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raverbashing
Tidal forces cause a lot of stress on celestial bodies.

The Moon is tidally locked to Earth. Its rotational energy was spent by
rotating it while being tidally pulled.

A good analogy is: get a rubber ball, squeeze it on a flat surface and roll it
(while squeezing it). That's what happened to the Moon.

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wahern
That can't be strictly true, otherwise we wouldn't be able to extract energy
from the tides. What am I missing?

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MaulingMonkey
> That can't be strictly true,

That The Moon is tidally locked to Earth? It's a one way relationship - The
Moon is tidally locked to Earth, but Earth isn't tidally locked to The Moon.

I assume you'd have trouble extracting as much energy from any tides that
might exist on The Moon, if it had liquid oceans.

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wahern
No. I was referring to

    
    
      "Its rotational energy was spent"
    

or rephrased

    
    
      "Tidal forces cause a lot of stress on celestial bodies",
      but not with the Earth-Moon system because the Moon's
      "rotational energy was spent".
    

raverbashing's point as I read it was that while tidal forces matter on
celestial bodies (i.e. not in the Earth-Moon system) they no longer matter in
the Earth-Moon system because the Moon is tidally locked.

I'm not disputing that the Moon is tidally locked, just the consequences in
terms of tidal forces. But perhaps the issue (and maybe err) is in confusing
rotational energy with orbital energy and the relationship to tidal forces.

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raverbashing
You misunderstood me

> "Tidal forces cause a lot of stress on celestial bodies",

Correct

> but not with the Earth-Moon system because the Moon's "rotational energy was
> spent".

Not _now_. But the Moon is still stretched tidally (and permanently in that
position)

It causes a lot of stress when the tidal pull happens while the body rotates
(w.r.t their main "puller" \- the Moon rotates, but not relative to the Earth)

And this pulling/stretching is what caused the Moon to stop rotating

Maybe Wikipedia explains it better
[https://en.wikipedia.org/wiki/Tidal_locking](https://en.wikipedia.org/wiki/Tidal_locking)

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okiedipshiz
I can confirm, we didn't have gravity here in Oklahoma until the 2000s.

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tehchromic
Queue the fracking-causes-quakes deniers! I can hear the floor speeches
already.

