1. Earth’s Crust In Motion
Earthquakes
Earth’s Crust In Motion

2. Guide For Reading How does stress forces affect rock?
Why do faults form and where do they occur?
How does movement along faults change Earth’s surface?

3. Earthquakes
Earthquake: The shaking that results from the movement of rock beneath Earth’s surface

4. Earth’s plates create powerful forces that ___ or ___ the rock in the crust.
squeeze
pull

5. Stress
Stress: A force that acts on rock to change its shape or volume

6. What is Volume?
The amount of space an object takes up

7. Energy is stored in rock until the rock ______________.
either breaks or changes shape

8. Shearing
Shearing: Stress that pushes a mass of a rock in opposite, horizontal directions

9. Tension
Tension: Stress that stretches rocks so that it becomes thinner in the middle

10. Compression
Stress that squeezes rock until it folds or breaks

11. 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

12. 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

13. Checkpoint How does deformation change Earth’s surface?
It causes it to:
Bend
Stretch
Break
Tilt
Fold
Slide

14. 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

15. Faults
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

16. Strike-Slip Faults
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

17. Normal Faults A type of fault where the hanging wall slides downward
Tension forces cause normal faults

18. 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

19. Reverse Faults A type of fault where the hanging wall slides up
Compression forces cause reverse faults

21. Figure 5: 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

22. Guide For Reading: Why do faults form and where do they occur?
Faults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the crust so much that the crust breaks

23. Checkpoint: What are the three types of fault
Checkpoint: 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

24. What is friction?
A force that opposes the motion of one surface as it moves across another surface

25. Friction exists because…
surfaces are not perfectly smooth.

26. 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

27. 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

28. 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

29. The San Andreas fault in California is a transform boundary that contains ___ stress.
high

30. Fault-Block Mountain
A mountain that forms where a normal fault uplifts a block of rock

31. 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

32. Folds
A bend in rock that forms where part of Earth’s crust is compressed

33. 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

34. Anticline
Anticline: An upward fold in rock formed by compression of Earth’s crust

35. An example of an anticline is the _________.
Black Hills of South Dakota

36. When and how did this location form?
Black Hills began to form about 65 million years ago

37. Syncline
Syncline: A downward fold in rock formed by tension in Earth’s crust

38. An example of a syncline is the _____.
Illinois Basin

39. This syncline stretches _____ from the western side of _____ through the state of _____.
250 kilometers
Indiana
Illinois

40. Plateaus
A large area of flat land elevated high above sea level

41. 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