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GLG310 Structural Geology
10 October 2013 GLG310 Structural Geology
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GLG310 Structural Geology
sd is differential
stress
-Engelder, 1993,
Stress regimes in
the lithosphere,
Princeton Univ.
Press
10 October 2013 GLG510 Advanced Structural Geology
Rheology:
“science of deformation and flow
of matter”
or
relationship between stress and
strain
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Idealized Elastic Material Linear relationship
between force and
extension (Hooke,
1676):
• Ut tensio sic uis
• As extension so the
force
• Analogous to spring
constant
http://www.see.leeds.ac.uk/structure
/rheology/hooke.htm
GLG310 Structural Geology
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10 October 2013 GLG510 Advanced Structural Geology
E (young’s modulus)
= d sa/d ea
Units of stress
-Pollard and Fletcher, 2005
10 October 2013 GLG310 Structural Geology
http://silver.neep.wisc.edu/~lakes/PoissonIntro.html
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10 October 2013 GLG510 Advanced Structural Geology
sa = f/A
ea = (b-B)/B
sp = 0
ep = (w-W)/W
n = - ep / ea
(Poisson ratio)
Measures
compressibility
Axial versus
transverse
deformation
Idealized Elastic Material
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10 October 2013 GLG510 Advanced Structural Geology
Stiffness and strength “Lest there be any possible, probably, shadow of
doubt, strength is not, repeat not, the same thing as stiffness. Stiffness, or Young’s modulus or E, is concerned with how stiff, flexible, springy or floppy a material is. Strength is the force or stress needed to break a thing. A biscuit is stiff but weak, steel is stiff and strong, nylon is flexible (low E and strong), raspberry jelly is flexible (low E) and weak. The two properties together describe a solid about as well as you can reasonably expect two figures to do.”
(Gordon, New science of strong materials, 2006)
http://www.see.leeds.ac.uk/structure/rhe
ology/inelastic.htm
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Plasticity • Steady deformation at yield strength
Plasticity • Steady deformation at yield strength
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10 October 2013 GLG510 Advanced Structural Geology
Viscosity • Strain rate proportional to differential stress
10 October 2013 GLG310 Structural Geology
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10 October 2013 GLG310 Structural Geology
http://www.youtube.com/watch?v=GxdfoJoWNE4
Variations in mechanical behavior
10 October 2013 GLG310 Structural Geology
Rock deformation experiments
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10 October 2013 GLG310 Structural Geology
GLG310 Structural Geology
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10 October 2013 GLG310 Structural Geology
http://www.youtube.com/watch?v=n4ZAb-p-dIw
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http://maydamedia.com/Images/Chapter11/Chart11.1.jpg
Rocks can flow: salt ascends
through overlying sediments
because it is bouyant
10 October 2013 GLG310 Structural Geology