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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.
I thought I felt lighter this morning...
I have a lot to keep track of, what with my checkbook, blogs, email, vehicle oil changes and tire rotation, bills, and keeping various client networks running.
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.
Raise your children as if you were teaching them to raise your grandchildren, because you are.
Brought to you by the Department of Redundancy Department...
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.
If half the earth moves relative to the other half, I'd think we'd have bigger problems.
God is dead, Nietzsche is dead, and I'm not feeling particularly good myself.
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.
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. :)