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TeethWhitener

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jim mcnamara

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https://en.wikipedia.org/wiki/P-wave P-waves from earthquakes are very low frequency sound waves.Typical values for P-wave velocity in earthquakes are in the range 5 to8 km/s. The precise speed varies according to the region of the Earth's interior, from less than6 km/sin the Earth's crust to13 km/sthrough the core.

Sound waves are in fact compression waves: http://www.physicsclassroom.com/class/sound/Lesson-1/Sound-is-a-Pressure-Wave

See Birch's law : https://en.wikipedia.org/wiki/Birch's_law which holds for materials not under enormous pressure. Which seems to be somewhat at odds to what @TeethWhitener indicated.

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davenn

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well not entirely, as in the earth, higher density will generally be directly proportional higher pressure, so no problem thereSee Birch's law : https://en.wikipedia.org/wiki/Birch's_law which holds for materials not under enormous pressure. Which seems to be somewhat at odds to what @TeethWhitener indicated.

It's just that you can have high density materials that don't need to be under high pressure, eg a block of lead

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TeethWhitener

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The velocity of sound has a very simple functional form:https://en.wikipedia.org/wiki/P-wave P-waves from earthquakes are very low frequency sound waves.

Sound waves are in fact compression waves: http://www.physicsclassroom.com/class/sound/Lesson-1/Sound-is-a-Pressure-Wave

See Birch's law : https://en.wikipedia.org/wiki/Birch's_law which holds for materials not under enormous pressure. Which seems to be somewhat at odds to what @TeethWhitener indicated.

[tex]c=\sqrt{\frac{K}{\rho}}[/tex]

Where c is velocity of sound, K is bulk modulus, and [itex]\rho[/itex] is density.

EDIT: The discrepancy between Birch's law and the Newton-Laplace law (above) really bugged me, so I did some digging, thinking maybe Birch's law was the first few terms of a Taylor series approximating Newton-Laplace. The only thing I could really find were some "Birch Diagrams" from old geology papers, where the empirical linear velocity-density relationship from Birch's law is given by two points per material.

Example: http://onlinelibrary.wiley.com/doi/10.1029/JB078i029p06926/epdf

So here's where I'm stuck (and maybe we need a geologist to sort this out): are they really drawing a general law from two points of data? Because in that case, of course you get a linear relationship. So what gives? Is there some assumption in Newton-Laplace that doesn't apply here? Inhomogeneity, shear, dispersion, etc.? I dunno.

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http://www.engineeringtoolbox.com/sound-speed-solids-d_713.html

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