1. Earth’s Crust in Motion
EQ: How do stress forces affect rock?

2. EQ: How do stress forces affect rock?
Earthquakes
Earthquake: The shaking that results from the movement of rock beneath Earth’s surface
EQ: How do stress forces affect rock?

3. Two powerful forces that change rock in the Earth’s crust:
Stress
Friction

4. Stress Stress: A force that acts on rock to change its shape or volume
EQ: How do stress forces affect rock?

5. What is Volume? The amount of space an object takes up
EQ: How do stress forces affect rock?

6. Energy is stored in rock until the rock either breaks or changes shape
EQ: How do stress forces affect rock?

7. Shearing
Shearing: Stress that pushes a mass of a rock in opposite, horizontal directions
EQ: How do stress forces affect rock?

8. EQ: How do stress forces affect rock?
Tension
Tension: Stress that stretches rocks so that it becomes thinner in the middle
EQ: How do stress forces affect rock?

9. EQ: How do stress forces affect rock?
Compression
Stress that squeezes rock until it folds or breaks
EQ: How do stress forces affect rock?

10. Figure 2: If shearing continues to tug at the slab of rock in B, what will happen to the rock?
The rock will break; the two parts will move in opposite directions
EQ: How do stress forces affect rock?

11. EQ: How do stress forces affect rock?
Deformation
Deformation: A change in the volume or shape of Earth’s crust
Most changes in the crust occur so slowly that they can not be observed directly
EQ: How do stress forces affect rock?

12. Checkpoint (Page 55): How does deformation change Earth’s surface?
It causes it to:
Bend
Stretch
Break
Tilt
Fold
Slide

13. Guide For Reading: How does stress forces affect rock?
The three kinds of forces that affect rock are:
Shearing
The rocks break and slip apart
Tension
The rock stretches and becomes thin in the middle
Compression
The rock squeezes until it folds or breaks
These stresses work over millions of years to change the shape and volume of rock

14. EQ: How do stress forces affect rock?
Faults
EQ: How do stress forces affect rock?
A break in the Earth’s crust where slabs of rock slip past each other
Faults occur when enough stress builds up in rock
Rocks on both sides of the fault can move up or down, or sideways

15. EQ: How do stress forces affect rock?
Strike-Slip Faults
EQ: How do stress forces affect rock?
A type of fault where rocks on either side move past each other sideways with little up-or down motion.
Shearing causes these types of faults

16. EQ: How do stress forces affect rock?
Normal Faults
A type of fault where the hanging wall slides downward
Tension forces cause normal faults
EQ: How do stress forces affect rock?

17. Hanging Wall & Footwall
Hanging wall: The block of rock that forms the upper half of a fault
Footwall: The block of rock that forms the lower half of a fault
EQ: How do stress forces affect rock?

18. EQ: How do stress forces affect rock?
Reverse Faults
A type of fault where the hanging wall slides up
Compression forces cause reverse faults
EQ: How do stress forces affect rock?

19. Checkpoint (Page 57): What are the three types of fault
Checkpoint (Page 57): What are the three types of fault? What force of deformation produce each?
Strike-slip faults
Produced by shearing
Normal faults
Produced by tension
Reverse faults
Produced by compression

20. Why do faults form and where do they occur?
Plate move and they compress, pull or shear the crust so much it breaks
Faults occur along plate boundaries

21. EQ: How do stress forces affect rock?

22. EQ: How do stress forces affect rock?
Which half of the reverse fault slid up and across to form this mountain, hanging wall or the footwall? Explain.
The hanging wall slipped up and across. If the footwall had moved up, the fault would be called a normal fault
EQ: How do stress forces affect rock?

23. EQ: How do stress forces affect rock?
What is friction?
A force that opposes the motion of one surface as it moves across another surface
It exists because rocks are not perfectly smooth
EQ: How do stress forces affect rock?

24. Describe what occurs when the friction along a fault line is low.
The rocks on both sides of the fault slide by each other without much sticking
EQ: How do stress forces affect rock?

25. Describe what occurs when the friction along a fault line is moderate.
The sides of the fault jam together
From time to time they jerk free
Small earthquakes occur
EQ: How do stress forces affect rock?

26. Describe what occurs when the friction along a fault line is high.
Both sides of the fault lock together and do not move
The stress increases until it is strong enough to overcome the force of friction
Larger and/or more frequent earthquakes will occur
EQ: How do stress forces affect rock?

27. EQ: How do stress forces affect rock?
Fault-Block Mountain
EQ: How do stress forces affect rock?
A mountain that forms where a normal fault uplifts a block of rock

28. How does the process of a fault-block mountain begin?
EQ: How do stress forces affect rock?
How does the process of a fault-block mountain begin?
Where two plates move away from each other, tension forces create many normal faults
When two of these normal faults form parallel to each other, a block of rock is left lying between them
As the hanging wall of each normal fault slips downward, the block in between moves upward
When a block of rock lying between two normal faults slides downward, a valley forms

29. EQ: How do stress forces affect rock?
Folds
EQ: How do stress forces affect rock?
A bend in rock that forms where part of Earth’s crust is compressed

30. How does the compression of two plates cause an earthquake?
The collisions of two plates can cause compression and folding of the crust
Such plate collisions also lead to earthquakes, because folding rock can fracture and produce faults
EQ: How do stress forces affect rock?

31. EQ: How do stress forces affect rock?
Anticline
Anticline: An upward fold in rock formed by compression of Earth’s crust
EQ: How do stress forces affect rock?

32. EQ: How do stress forces affect rock?
Syncline
EQ: How do stress forces affect rock?
Syncline: A downward fold in rock formed by tension in Earth’s crust

33. EQ: How do stress forces affect rock?
Plateaus
A large area of flat land elevated high above sea level
EQ: How do stress forces affect rock?

34. Guide For Reading: How does movement along faults change Earth’s surface?
Over millions of years, fault movement can change a flat plain into a towering mountain range
Mountain ranges can form from:
Fault – block mountain
Folding
Anticlines & Synclines
Plateaus