No. 135: MAY-JUN 2001
In a deeper sense, there are new measurements suggesting that the earth's solid crust also contracts by minute amounts in an annual cycle. For example, 50 GPS (Global Positioning System) stations in northeastern Japan detect east-west contractions of the crust of about 50 millimeters/year. The compressions are 15% faster in the fall and 15% slower in the spring. The same rhythmic squeezing has been discerned in a 150-meter tunnel dug into granite bedrock in the same region.
To these instrument measurements can be added the strong tendency of some major volcanos to erupt in the fall when the biggest squeeze is on. The analogy of toothpaste being squeezed out of a tube is inescapable here!
The cause of these annual "breathing" cycles is uncertain.
(Kerr, Richard A.; "Earth's Breathing Lessons," Science, 291:584, 2001.)
Comment. In principle, gravity waves could cause miniscule contractions of the crust, but it is difficult to see how they could have an annual cycle.
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