1. Folds, Faults and the Deformation of Earth’s Crust
Cockscomb structure in Utah

2. What Happened to this car? Pre-crash
1984
Post-crash
It was deformed (folded) because of the collision

3. Coincidentally, note how this car is so much more safe
The car deformed like an accordion
while the passenger compartment did not suffer.
That is possible because the front part of the
car absorbs the stress by folding.

4. Stress vs. Strain The force applied to some body is the stress.
The changes to that body are the strain that is recorded.
You work very hard lifting things.
Your back is strained.

5. Silly Putty Silly Putty absorbs the Stress that is
applied to it when it hits the floor. However, the Strain is released when it bounces away from that Stress.
Silly Putty is elastic, it bounces if it were dropped on the floor.

6. The Slinky
The Slinky is Elastic i.e. it can be stretched and stretched but it snaps back to its original length.

7. The 1st Type of Stress:
Compression: occurs when crustal rocks are squeezed together
Can reduce the volume of rocks, can push the rocks higher up or deeper down into the crust

8. The 2nd Type of Stress Tension: the force that pulls rocks apart
Rocks that are pulled apart by tension tend to become thinner

9. The Final Type of Stress
Shearing: pushes rocks in opposite horizontal directions
These rocks bend, twist, or break apart as they slide past each other.

10. The Deformed Earth
Plate tectonics and the movement of lithospheric plates causes the Earth’s crust to DEFORM….
“No, no, don’t look at me!!! I’m hideous!!”

11. Isostasy and the Mattress Test
Have you ever seen the commercial for foam mattresses where they place a glass of red wine on one side and a man jumps up and down on the other side?
Isostasy: the balancing of up-and-down movements of the earth’s crust.

12. What happened to these rocks?
What evidence do you see, which caused your interpretation?

13. Which of the following types of tectonic forces tends to squeeze and shorten a rock body?
A. compressive forces
B. shearing forces
C. tensional forces
D. all of the above

14. Which of the following types of tectonic forces tends to squeeze and shorten a rock body?
A. compressive forces
B. shearing forces
C. tensional forces
D. all of the above
This looks like the safe car
because of how it folded

15. What type of forces dominate at convergent plate margins?
compressive forces
B. shearing forces
C. tensional forces
D. torsional forces

16. What type of forces dominate at convergent plate margins?
A. compressive forces
B. shearing forces
C. tensional forces
D. torsional forces

17. The San Andreas Fault is a result of what type of forces?
A. compressive forces
B. shearing forces
C. tensional forces
D. all of the above

18. The San Andreas Fault is a result of what type of forces?
A. compressive forces
B. shearing forces
C. tensional forces
D. all of the above

19. Which of the following statements best describes the behavior of rocks during deformation?
A. Brittle materials deform by faulting, whereas ductile materials deform by folding.
B. Brittle materials deform by folding, whereas ductile materials deform by faulting.
C. Both brittle and ductile materials deform by faulting.
D. Both brittle and ductile materials deform by folding.

20. Pressure and Temperature
Which of the following statements best describes the behavior of rocks during deformation?
ductile materials
deform by folding
T- High or Low?
P- High or Low?
Marble is special
because it can be
Brittle or Ductile
depending on
Pressure and Temperature
Brittle materials
deform by faulting
T- High or Low?
P- High or Low?

21. These are Sedimentary Rocks
They
must
been
have
The principles of
Original Horizontality
and Superposition
apply-
folded
But these layers are not any longer Horizontal

22. These Rocks were Brittle so they were fractured to form a Fault
The faults were not caused
by Compression Forces

23. These Rocks were Brittle so they were fractured to form a Fault
The faults were not caused by Compression Forces
The length of the rock formation
is greater than the original length
because of the type of fault a b
The faults were caused
by Tension

24. More FOLDED Sedimentary Rocks
But HOW MUCH have they been folded? or
How can one measure the angle that they
have rotated from the original horizontal?

25. Measuring the orientation of a surface

26. Rocks also have a Strike and Dip
Strike- the direction to which the horizontal line points

27. Geological Map shows the rocks exposed on surface over which you are walking

28. 3- D View of Geological Structures
Plan view i.e. the surface that one looks down to see
The same
formation
Outcrop the view where the rocks have been vertically cut through for a new highway or natural erosion

29. Ductile Materials and Deformation
They undergo Plastic Deformation i.e.
they change shape and do not break but
do not return to their original form

30. Combinations of Stresses

31. A Rift Valley formed by Extension

32. Fresh Scarp Face showing surface exposed by a very recent earthquake* *

33. Symmetrical Folds