effect of erosion on mountain building background on work budget background on erosion erosion...
TRANSCRIPT
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Effect of erosion on mountain building
Background on work budget
Background on erosion
Erosion exercise
Data analysis
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Is the Earth Lazy?
whatever
Do fault systems evolve in order to minimize the total work?
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Evidence of lazy Earth
Geometry of spreading centers [Sleep, 1979] and mudcracks reflects work minimization
Faults become more smooth with greater slip
Strike-slip traces [e.g. Wesnousky, 1988], extensional fault traces [Gupta et al., 1998], and lab [Scholz, 1990].
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Forces within wedges
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Work terms
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Underthrust-Accretion Cycle
a) Accretion: new forethrust
b) Underthrusting
c) Accretion: new forethrust
d) Underthrusting
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Sandbox experiments
Adams et al. 2001, JSG
Particle Integrated Velocity records the development of accreting forethrust within10 cm of contraction
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Model Set-Up
Simulate 0.5 cm of contraction
Forethrust
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Thrust Sheet Growth
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Conclusions thus far…
Sandboxes are lazy!The Earth might be
lazy.
?
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Equilibrium
At equilibrium the ratio of wedge thickness to wedge length is constant.
Erosion can disrupt this equilibrium
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6 8 10 12 14
displacement (cm)
wedge thickness/length
high frictionlow friction
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Erosion
Iceland
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Erosion
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Watch Mario movie
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Erosion Experiment
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# turns Displacement (cm)
Wedge thickness
Wedge length
Wedge thickness
Wedge length
0 0
20
40
60
erosion
80
100
120
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Implications
After erosion the wedge thickens rather than lengthening. Can accommodate contraction efficiently along the old faults
On the non-erosion side, wedge must constantly lengthen because the old faults are buried under heavy sand.
Fault system adjusts to slip along the most efficient path <- earth is lazy!