>An analogy would be a man swimming 20 00 leagues beneath the sea is under
>greater pressure than when not swimming, sorry, it just doesn't seem to fit.
>The pressure due to the water above would not alter significantly because of
>movement at a particular depth.
>
Dear Daryl,
If the swimming man do not create an overpressure (even if very very
small), it will not be able to move at all even in water. For the
same reason airplanes can fly (overpressure beneath wings)!
But the Earth is not made of water nor of any material with viscosity
similar to that of water. Also, it is not so homogeneous, and the
reason of overpressure is due to viscosity contrasts between rocks
during deformation. See for instance the differences between the
Voigt and Reuss bounds for elasticity (or if you want Taylor and
Sachs approximations in the case of plastic deformation).
Maybe the question is more a preservation problem. What happens to a
rock and minerals when the differential stresses are released?
Luigi Burlini
Rock Deformation Lab, ETH ZENTRUM,
Sonnegstrasse 5, CH-8092 Zürich
Tel. 0041-1-632.3708 (Office), 3709 (Lab), Fax 632.1080
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