Scientists Measure Gravity Change From Earthquake 99
Science Daily is reporting that scientists were able to use satellite data to watch changes in the Earth's surface caused by a massive earthquake. These changes had two major measurable effects on the region. The massive uplift in the seafloor changed GPS measurements, and the density of the rock beneath the seafloor changed which produced a detectable change in gravity.
Feels lighter (Score:5, Funny)
Gravity waves discovered? (Score:3, Funny)
Being redundant can be fun, as long as its differe (Score:1)
Re:Feels lighter (Score:2)
Re:Feels lighter (Score:2)
Re:Feels lighter (Score:1)
Re:Feels lighter (Score:3, Funny)
Re:Feels lighter (Score:2)
"massive earthquake" (Score:1, Funny)
Re:"massive earthquake" (Score:1)
Re:"massive earthquake" (Score:2)
Re:"massive earthquake" (Score:2)
Re:"massive earthquake" (Score:1)
So, how much is it now? (Score:5, Funny)
So I'd appreciate it if someone could keep track of this whole gravity situation, and just give me a summary. Let me know if we're all about to go floating off into LEO, but otherwise, keep the announcements to a minimum.
Re:So, how much is it now? (Score:1)
Because Slashdot needs more Apple rumours and less science reporting.
KFG
Re:So, how much is it now? (Score:2)
Re:So, how much is it now? (Score:2)
Don't worry, WWDC is next week.
Top-notch editing (Score:5, Funny)
Detecting "major" quakes - those measuring a magnitude of 7 to 8.9 - which occur frequently is being investigated. NASA's planned extension of the current mission, dubbed GRACE 2, and its enhanced instrumentation should aid in that effort.
However, Han is hopeful that NASA's planned expansion of the current mission, dubbed GRACE 2, and its enhanced instrumentation, might allow the detection of "major" quakes - those measuring a magnitude 7 to 8.9 - which occur frequently.
Re:Top-notch editing (Score:2, Informative)
Re:Top-notch editing (Score:3, Funny)
Re:Top-notch editing (Score:1)
Or they maybe were anticipating that they were to be "quoted" here (were dupes have kind of a tradition as I was informed), which then would be precognition [wikipedia.org].
CC.
Global Gravity Change is Real (Score:2, Funny)
If we don't take this threat seriously, we will all be smashed flat, like pancakes, and grilled by global warming.
Unconfirmed reports indicate that giant bird-like aliens will arrive shortly, and revel in the pancake carnage, gorging on the waste like so many crows on road kill. The same sources said they do not wish to imply that the aliens are in
I'd mod parent funny, but that's just me (Score:3, Insightful)
If I had them, well, I might give that one - it is almost funny, in a Jon Stewart kind of way.
magnitude of the change (Score:3, Interesting)
Or more interesting dose anyone have a map of the earth and differences in gravity in different areas? (I smell a new google map)
Just my 2 cents
Re:magnitude of the change (Score:1, Insightful)
Of course, sport is more important than science! Why don't you go measure the gravity effects of your glass of water? Oh, that's right, you don't know how to do that. This may not be a groundbreaking development, but it may be a newsworthy accomplishment.
Re:magnitude of the change (Score:1)
Re:magnitude of the change (Score:1)
Re:magnitude of the change (Score:2, Funny)
Re:magnitude of the change (Score:1)
Re:magnitude of the change (Score:3, Funny)
And all the fat people can move to neighborhoods with lower gravity, Voila! Instant weight loss.
Re:magnitude of the change (Score:2)
Re:magnitude of the change (Score:4, Informative)
Meaning it should be in the 0.01 m/s^2 range.
For the simple reason that if it were anymore, the earth would deform to counter that imbalance (molten core, you know).
That, btw, also limits the height of mountains to about 10-12Km on earth (compare to mars, where to lower gravity constant allowed much larger volcanos)
Re:magnitude of the change (Score:5, Informative)
The full paper as well as a very nice layman's introduction in the Perspectives section is in this month's issue of Science. (Sorry - subscription only. But you may be able to find the text on a preprint server. I'm no geologist, but I haven't been able to find it in any of the obvious places.)
Basically, they map out a change of 15 microgals (1 gal = 1 cm/s^2) or around 1.5e-8 of the average gravitational field on the earth.
By comparison, the variation in g with latitude (at constant elevation) is around 0.5 percent, or 300'000 times as much. Variation associated with local geology is around 100 times smaller, but still swamps this earthquake signal.
What's cool about this measurement isn't that they're measuring something big enough to have any effect on humans, but rather that they're able to measure such a tiny effect at all.
There are all sorts of processes going on in the earth and in the oceans that involve movements of comparable amounts of mass: changes in glacier and polar icecaps, ocean-atmosphere gas exchange, deep sea current and temperature changes, movement and depletion of underground water, fast moving magma associated with volcanos, slow tectonic changes, etc. And now it seems like it's also helpful in trying to construct detailed models of an earthquake.
Incidentally, if you were an athlete trying to cash in on lower gravity, you'd be better off training in the Chilean highlands and competing in Puerto Rico - but it still wouldn't help you much, especially compared to biological effects and day to day variation in performance. (http://www.csr.utexas.edu/grace/publications/fac
Re:magnitude of the change (Score:2)
Cleary I haven't had enough caffine yet today.
Re:magnitude of the change (Score:2)
But that comment seems to have vanished. Perhaps I hit the posting time-limit and didn't notice.
I think I'd better stop posting now before I get myself into *real* trouble.
Oh well. At least it gave me a chance to notice a a Vernor Vinge fan posting in this threat. Always nice to run across one of those.
Re:magnitude of the change (Score:1)
Re:magnitude of the change (Score:1, Interesting)
The Earth's gravity can only change with added or reduced mass. This article hints that it is the amount of gravity that has changed which isn't possible through this earthquake. What is possible is that the vector of gravity; (typically down twards the center of the earth) has been changed since dense matter has moved drastically.
On a side note, the earth tends to pick up 200 lbs every year due to meteorites. If there's any change in the ammount of gravity, that is what's doing it!
Re:magnitude of the change (Score:2)
Re:magnitude of the change (Score:2)
Re:magnitude of the change (Score:1)
The same amount of gravity is there, as before the earthquake. That has not and cannot change. What has changed is which direction (or as I called it, "vector") that the gravity is pulling.
As the vector changes, your one dimentional equipment for measuring gravity is sure to have a change in values. Go back to Highschool Trig.
Re:magnitude of the change (Score:2)
Death knoll for 'intelligent falling'? (Score:3, Funny)
Troll? (Score:1)
Re:how does this work? (Score:3, Interesting)
Yes.
Put a cement block on the floor in front of you. Now stand on it.
Ta da! Instant local gravity increase, because there is now more mass underneath you.
KFG
Re:how does this work? (Score:1)
Re:how does this work? (Score:1)
Whether that is true or not is left as an exercise for the student.
KFG
Re:how does this work? (Score:1)
-Ed
Re:how does this work? (Score:1)
But you are father away from the mass on the opposite side, reducing its contribution to the total force.
Turns out that if you average all the forces it works out to the same as if all the mass were concentrated at the Earth's center.
If you dig a hole and jump in gravity will be decreased, even though you're closer to the center, because the average force exerted on you by the entire shell of
Re:how does this work? (Score:1)
-Ed
Re:how does this work? (Score:1)
But the force of gravity also follows the inverse square law, get twice as far away and you quarter the force of gravity.
So if your added mass necessarily pushes you farther away from the center the force will fall off due to distance faster than it increases due to mass, lowering the net force, unless your cement block is very massive. Say about 1000 Kg.
KFG
Re:how does this work? (Score:2, Informative)
Re:how does this work? (Score:2, Funny)
I can't help it if you didn't notice the cement block shaped hole in the floor into which the cement block was supposed to be inserted.
I think you can agree . .
Not until you show your work, no, I cannot.
KFG
Re:how does this work? (Score:2)
Re:how does this work? (Score:1)
How about we put our g meter on top of a stool, take a reading, and then shove a concrete block under the stool?
KFG
Re:how does this work? (Score:2)
A terrestrial mass only a couple of kilometers in di
Re:how does this work? (Score:1)
I've stood on a bathroom scale trying to measure this but my instruments are either too insensitive or are too greatly affected by the tremendous resultant atmospheric change. Any ideas?
Re:how does this work? (Score:1)
Use a satellite.
Contemplate other phenomenon that might affect the outcome of the experiment (hint: think of a balloon) and propose a means of compensating for their effect.
If the satellite turns out to be insufficiently precise ponder the limits of measurment and the concept of significance
Re:how does this work? (Score:2)
Really?
What I mean is this: does the extra attractive force between you and the cement block more than compensate for the extra distance you've put between yourself and the earth's center of mass (which would tend to decrease the gravitational force you feel from earth)?
Re:how does this work? (Score:1)
Wellllllll, not with a typical cement block, no.
does the extra attractive force between you and the cement block more than compensate for the extra distance you've put between yourself and the earth's center of mass
Gravity falls off by the inverse of the square of the distance. If your cement block is equal in mass to the average of the column of Earth underneath you the mass is only going up linearly with distance and the total force will go down. If it's equal to the square of the average mass you'
Signals in context (Score:1, Interesting)
I think there's no magic bullet for quake prediction, but the solution is a very holistic thing by aggregating lots and lots of different measurements. For example the
GPS is relative to exactly where? (Score:5, Interesting)
If GPS is tied to some NAVY building in Maryland and the building moves, do we then declare that the building DID NOT MOVE because it is by definition in a particular place? Everybody else moved?
(I do not in fact know: it could be an Air Force cave in the Rocky Mountains, etc.)
If half of the Earth moves relative to the other half, which set of property owners has a problem?
Re:GPS is relative to exactly where? (Score:5, Funny)
Moves how much? (Score:3, Interesting)
If it moves "a little", the people with a problem with be the ones that are poorer - as usual. By definiton the more well-to-do have the means to fix stuff (or higher a better lawyer to get the "new" property lines drawn in their favor :-)
On the other hand, if it moves "a bit", (like "end of the world as we know it") then maybe you would have been better off as a hunter gatherer, already in tune with the pr
Re:GPS is relative to exactly where? (Score:1)
Uhhhhh... somebody correct me if I'm wrong, but so far as I was aware, the only thing GPS is "tied to" is a ring of satellites in geosynchronous orbit above the Earth, where they are mostly indifferent to earthquakes. Just because this article (rather vaguely) says that "GPS measurements" changed doesn't mean th
Re:GPS is relative to exactly where? (Score:5, Informative)
When you get a position fix from the GPS system, you are combining the information from several satellites, each of which is transmitting a signal of the form, "My name is GPS _X_, I sent this message at time _Y_ from the approximate location _Z_" A GPS receiver triangulates a position by calculating the distance to several satellites, using Center-Of-Earth coordinates.
It's true that your position is calculated relative to the satellites, but in order for the satellite to know where it was when it sent the message, there has to be pretty accurate data about its precise orbit, which depends intimately on the shape and mass distribution of the earth ("Geosynchronous" is only approximate), so that the final location in Latitude.-Longitude.-Altitude can be given relative to the center of the earth. A big quake could certainly shift things around enough to alter the orbit, which is probably what these researchers were talking about.
On the other hand, for the purposes of surveying on earth, its certainly conceivable that one could define property lines in relation to the locations of particular GPS antennae, fixed into bedrock or something, and that if those moved, things would be all kerflooey. But that's not new to GPS surveying, since its always been done relative to the location of particular fixed monuments. :)
I think wikipedia may have the answer (Score:2)
Hawaii, Kwajalein, Ascension Island, Diego Garcia, Colorado Springs
Perhaps your GPS unit thus gives you a position relative to the average of those sites. That would be two spots in the Pacific Ocean, one in the Indian Ocean, one in the South Atlantic Ocean, and one in the Rocky Mountains. If things disagree, I'll bet Colorodo Springs wins the argument.
If you're in Asia or Europe and your land moves... oh well!
Re:GPS is relative to exactly where? (Score:2)
Re:GPS is relative to exactly where? (Score:2)
Re:GPS is relative to exactly where? (Score:2)
It's all based on averages. The motion of the crust in the biggest earthquakes is still insignificant compared to the total mass of the entire volume of the Earth so it doesn't really affect the GPS frame of reference. The e
Re:GPS is relative to exactly where? (Score:1)
Yes, because everyone knows the world revolves around the U S and A!
Joke Disclaimer: If you think this is flamebait, get a grip on yourself and lighten up.
Recalibrating Equipment (Score:2)
particle accelerators and moon phases (Score:1)
In other news... (Score:2, Funny)
I just have to say that... (Score:2)
Re:I just have to say that... (Score:2)
LIGO (Score:1)
Other gravity changes (Score:5, Interesting)
We were also told at the end of the practical about far more accuarte ways of measuring g, and that a university in Germany several decades ago had used this regularly as experimental training for graduate students. However, when the experiment was performed at different times of the year, a small but definte increase in g was noticed during the winter. More accurate measurements showed a sudden spike near the start of winter, followed by a slow decrease until the summer.
Professors were baffled, until someone remembered that the lab in which the experiments were carried out was above a coal cellar used to store a huge quantity of coal for burning during the winter.
Re:Other gravity changes (Score:1)
Re:Other gravity changes (Score:2)
Who needs a new geoid? (Score:3, Funny)
Ahh... (Score:1)
Big Earthquake (Score:1)
Given enough sensitivity in the instruments... (Score:1)
Re:Given enough sensitivity in the instruments... (Score:1)
Nerd Out (Score:2)