1. Table of Contents Forces in Earth’s Crust
Earthquakes and Seismic Waves
Monitoring Earthquakes
Earthquake Safety

2. Plate Tectonic Boundaries

3. Types of Stress - Forces in Earth’s Crust
The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.

4. Types of Stress - Forces in Earth’s Crust
The stress force called compression squeezes rock until it folds or breaks.

5. Types of Stress - Forces in Earth’s Crust
Stress that pushes a mass of rock in two opposite directions is called shearing.

6. Kinds of Faults - Forces in Earth’s Crust
Tension in Earth’s crust pulls rock apart, causing normal faults.

7. Kinds of Faults - Forces in Earth’s Crust
A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

8. Kinds of Faults - Forces in Earth’s Crust
In a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up and down motion.

9. Changing Earth’s Surface
- Forces in Earth’s Crust
Changing Earth’s Surface
Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.

10. Changing Earth’s Surface
- Forces in Earth’s Crust
Changing Earth’s Surface
Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.

11. Building Vocabulary - Forces in Earth’s Crust
A definition states the meaning of a word or phrase. As you read, write a definition of each Key Term in your own words.
Key Terms:
Examples:
hanging wall
footwall
strike-slip fault
anticline
syncline
plateau
Key Terms:
Examples:
stress
The block of rock that lies above a normal fault is called the hanging wall.
Stress is a force that acts on rock to change its shape or volume.
tension
The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.
The rock that lies below is called the footwall.
In a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up or down motion.
compression
The stress force called compression squeezes rock until it folds or breaks.
A fold in rock that bends upward into an arch is an anticline.
shearing
Stress that pushes a mass of rock in two opposite directions is called shearing.
A fold in rock that bends downward to form a valley is a syncline.
normal fault
Tension in Earth’s crust pulls rock apart, causing normal faults.
reverse fault
A plateau is a large area of flat land elevated high above sea level.
A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

12. Colorado Plateau

13. Click the SciLinks button for links on faults.
- Forces in Earth’s Crust
Links on Faults
Click the SciLinks button for links on faults.

14. End of Section: Forces in Earth’s Crust

15. Types of Seismic Waves - Earthquakes and Seismic Waves
Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.

16. Types of Seismic Waves - Earthquakes and Seismic Waves
P waves are seismic waves that compress and expand the ground like an accordion. S waves are seismic waves that vibrate from side to side as well as up and down.

17. Types of Seismic Waves - Earthquakes and Seismic Waves
Surface waves move more slowly than P waves and S waves, but they produce the most severe ground movements.

18. Seismic Waves Activity
- Earthquakes and Seismic Waves
Seismic Waves Activity
Click the Active Art button to open a browser window and access Active Art about seismic waves.

19. Measuring Earthquakes
- Earthquakes and Seismic Waves
Measuring Earthquakes
The Mercalli scale was developed to rate earthquakes according to the amount of damage at a given place.

20. Seismic Wave Speeds - Earthquakes and Seismic Waves
Seismographs at five observation stations recorded the arrival times of the P and S waves produced by an earthquake. These data are shown in the graph.

21. Seismic Wave Speeds - Earthquakes and Seismic Waves Reading Graphs:
What variable is shown on the x-axis of the graph? The y-axis?
X-axis––distance from the epicenter; y-axis––arrival time.

22. Seismic Wave Speeds - Earthquakes and Seismic Waves Reading Graphs:
How long did it take the S waves to travel 2,000 km?
7 minutes

23. Seismic Wave Speeds - Earthquakes and Seismic Waves Estimating:
How long did it take the P waves to travel 2,000 km?
4 minutes

24. Seismic Wave Speeds - Earthquakes and Seismic Waves Calculating:
What is the difference in the arrival times of the P waves and the S waves at 2,000 km? At 4,000 km?
2,000 = 3.5 minutes
4,000 = 4.5 minutes

25. Locating the Epicenter
- Earthquakes and Seismic Waves
Locating the Epicenter
Geologists use seismic waves to locate an earthquake’s epicenter.

26. Identifying Main Ideas
- Earthquakes and Seismic Waves
Identifying Main Ideas
As you read the section “Types of Seismic Waves,” write the main idea in a graphic organizer like the one below. Then write three supporting details. The supporting details further explain the main idea.
Main Idea
Detail
Seismic waves carry the energy of an earthquake.
P waves compress and expand the ground.
S waves vibrate from side to side as well as up and down.
Surface waves produce the most severe ground movements.

27. Seismic Waves in the Earth
- Earthquakes and Seismic Waves
Seismic Waves in the Earth
Click the Video button to watch a movie about seismic waves in the earth.

28. End of Section: Earthquakes and Seismic Waves

29. The Modern Seismograph
- Monitoring Earthquakes
The Modern Seismograph
Seismic waves cause the seismograph’s drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations.

30. Instruments That Monitor Faults
- Monitoring Earthquakes
Instruments That Monitor Faults
In trying to predict earthquakes, geologists have developed instruments to measure changes in elevation, tilting of the land surface, and ground movements along faults.

31. Using Seismographic Data
- Monitoring Earthquakes
Using Seismographic Data
The map shows the probability of a strong earthquake along the San Andreas fault. A high percent probability means that a quake is more likely to occur.

32. Sequencing - Monitoring Earthquakes
As you read, make a flowchart like the one below that shows how a seismograph produces a seismogram. Write each step of the process in a separate box in the order in which it occurs.
How a Seismograph Works
Incoming seismic waves
Vibrate the rotating drum
The suspended pen remains motionless and records the drum’s vibration.

33. Links on Earthquake Measurement
- Monitoring Earthquakes
Links on Earthquake Measurement
Click the SciLinks button for links on earthquake measurement.

34. End of Section: Monitoring Earthquakes

35. Earthquake Risk - Earthquake Safety
Geologists can determine earthquake risk by locating where faults are active and where past earthquakes have occurred.

36. How Earthquakes Cause Damage
- Earthquake Safety
How Earthquakes Cause Damage
A tsunami spreads out from an earthquake's epicenter and speeds across the ocean.

37. Designing Safer Buildings
- Earthquake Safety
Designing Safer Buildings
To reduce earthquake damage, new buildings must be made stronger and more flexible.

38. Asking Questions - Earthquake Safety
Before you read, preview the red headings and ask a what, how, or where question for each heading. As you read, write answers to your questions.
Question
Answer
Where is the quake risk highest?
Earthquake risk is the highest along faults and where past earthquakes have occurred.
How do earthquakes cause damage?
Earthquake damage occurs as a result of shaking, liquefaction, aftershocks, and tsunamis.
How can you stay safe during an earthquake?
The best way to stay safe during an earthquake is to drop, cover, and hold.
What makes buildings safe from earthquakes?
Buildings can be made safer by being built stronger and with greater flexibility.

39. Click the Video button to watch a movie about earthquake damage.
- Earthquake Safety
Earthquake Damage
Click the Video button to watch a movie about earthquake damage.

40. More on Earthquake Risk
- Earthquake Safety
More on Earthquake Risk
Click the PHSchool.com button for an activity about earthquake risk.

41. End of Section: Earthquake Safety

42. Graphic Organizer
Reverse
Tension
Shearing
Strike-slip

43. End of Section: Graphic Organizer