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Scientists Measure Gravity Change From Earthquake
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.
Really bland article I mean I can change the gravitation fields on my desk my moving my glass of water around and I do believe that is measurable. (Maybe not by a satellite.) So anyone out there have an idea of the magnitude of the change. Will athletes gain a boost there by training in a higher gravity environment? What are the effects of the lower gravity environment or is it so insignificant that who cares.
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
What we really want to know is can this data be fitted to measurements immediately before the quake. Since earthquakes are essentially relaxation oscillations in plate movement very careful extrapolation with some fancy signal processing techniques (linear prediction maybe) might be able to spot some features in the gravity field out in space.
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 gravometric measurements may say "there's about to be a quake somewhere on Earth, but we can't say where for sure" while more local measurements might help pin down the likely shift location.
With everything moving all over and us trying to define property lines (including international borders) reliably, we sure do have a mess.
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?
Is it in one spot . . .
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
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 primative conditions that arise.
Of course, if it is "really a lot" (end of the world.) Then the point is moot.
This issue is a bit more complicated than you think.
This reminds me a little of a physics practical I did this year. It was supposed to be the first practical where we would get a decent accuracy, measuring g using a pendulum to about 6 significant figures.
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.