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Gravitational pull 'has role in quakes'

bbc.com

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Re: Gravitational pull 'has role in quakes'

#21

Post by 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.

Re: Gravitational pull 'has role in quakes'

#22

Post by wahern »

raverbashing wrote: post #19

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.

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

Re: Gravitational pull 'has role in quakes'

#23

Post by antod »

jlmorton wrote: post #14
ProAm wrote: post #12

Earlier quoted context omitted.

But the actual phase has nothing to do with it, the moons position around the earth does. It's possible to have a full moon over head or a new moon over head, the gravitational pull will be the same regardless of the phase. It's purely coincidental about it being a full moon.

The phase is important because tidal forces are the sum of forces from both the Sun and the Moon. When the Moon is full, that is because the Moon is directly opposite the Sun. When the Moon is new, that is because it is directly in front of the Sun. This causes minimums and maximums in the tidal forces on the Earth.

> The phase is important because tidal forces are the sum of forces from both the Sun and the Moon. When the Moon is full, that is because the Moon is directly opposite the Sun. When the Moon is new, that is because it is directly in front of the Sun. This causes minimums and maximums in the tidal forces on the Earth.

More pedantically, both those phases cause a spring tide (max tidal range). A neap tide (min tidal range) is when the sun and the moon are at right angles to the earth.

Re: Gravitational pull 'has role in quakes'

#24

Post by MaulingMonkey »

wahern wrote: post #22
raverbashing wrote: post #19

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.

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

> 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.

Re: Gravitational pull 'has role in quakes'

#25

Post by wahern »

MaulingMonkey wrote: post #24
wahern wrote: post #22

Earlier quoted context omitted.

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

> 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.

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.

Re: Gravitational pull 'has role in quakes'

#26

Post by MaulingMonkey »

wahern wrote: post #25
MaulingMonkey wrote: post #24

Earlier quoted context omitted.

> 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.

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.…

Ahh. I interpreted more along the lines of the rephrasing: "... but not on the Moon because the Moon's 'rotational energy was spent'" - that is, no claim about Earth not still being under significant stress.

Taken as a whole, I read the comment as possibly along the lines of "This seems reasonable (or obvious) - you end up with dead lifeless geologically inert celestial bodies like the moon if you take away the stress of tidal forces / (varying) gravitational pull", as an example to contrast/compare against.

Re: Gravitational pull 'has role in quakes'

#27

Post by raverbashing »

wahern wrote: post #25
MaulingMonkey wrote: post #24

Earlier quoted context omitted.

> 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.

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.…

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

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