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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.
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?
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.