1. Earthquakes Chapter 8 Table of Contents
Section 1 What Are Earthquakes?
Section 2 Earthquake Measurement
Section 3 Earthquakes and Society

2. Chapter 8
Section 1 What Are Earthquakes?
Bellringer
What do you think an earthquake is? Do you think the way earthquakes are portrayed on television and in movies is accurate? Why or why not?
Write your answers in your science journal.

3. Objectives Chapter 8 Explain where earthquakes take place.
Section 1 What Are Earthquakes?
Objectives
Explain where earthquakes take place.
Explain what causes earthquakes.
Identify three different types of faults that occur at plate boundaries.
Describe how energy from earthquakes travels through the Earth.

4. What Are Earthquakes? Chapter 8
Section 1 What Are Earthquakes?
What Are Earthquakes?
There is more to earthquakes than just the shaking of the ground. An entire branch of Earth science, called seismology, is devoted to the study of earthquakes.
Earthquakes are complex, and they present many questions for seismologists, the scientists who study earthquakes.

5. Where Do Earthquakes Occur?
Chapter 8
Section 1 What Are Earthquakes?
Where Do Earthquakes Occur?
Most earthquakes take place near the edges of tectonic plates. This figure shows the Earth’s tectonic plates and the locations of recent major earthquakes.

6. Where Do Earthquakes Occur?, continued
Chapter 8
Section 1 What Are Earthquakes?
Where Do Earthquakes Occur?, continued
Tectonic plates move in different directions and at different speeds. As a result, numerous features called faults exist in the Earth’s crust.
A fault is a break in the Earth’s crust along which blocks of the crust slide relative to one another.
Earthquakes occur along faults because of this sliding.

7. What Causes Earthquakes?
Chapter 8
Section 1 What Are Earthquakes?
What Causes Earthquakes?
As tectonic plates move, stress increases along faults near the plates’ edges. In response to this stress, rock in the plates deforms.
Deformation is the change in the shape of rock in response to the stress of bending, tilting, and breaking of the Earth’s crust.

8. What Causes Earthquakes?, continued
Chapter 8
Section 1 What Are Earthquakes?
What Causes Earthquakes?, continued
Rock along a fault deforms in mainly two ways.
Rock deforms in a plastic manner, like a piece of molded clay, or in an elastic manner, like a rubber band.
Plastic deformation does not lead to earthquakes. Elastic deformation does. Like a rubber band, rock can be stretched only so far before it breaks.

9. What Causes Earthquakes?, continued
Chapter 8
Section 1 What Are Earthquakes?
What Causes Earthquakes?, continued
Elastic rebound is the sudden return of elastically deformed rock to its undeformed shape. Elastic rebound occurs when more stress is applied to rock than the rock can withstand.
During elastic rebound, energy is released. Some of this energy travels as seismic waves, which cause an earthquake.

10. Elastic Deformation and Elastic Rebound
Chapter 8
Section 1 What Are Earthquakes?
Elastic Deformation and Elastic Rebound
Click below to watch the Visual Concept.
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Visual Concept

11. Faults at Tectonic Plate Boundaries
Chapter 8
Section 1 What Are Earthquakes?
Faults at Tectonic Plate Boundaries
A specific type of plate motion takes place at different tectonic plate boundaries.
Each type of motion creates a particular kind of fault that can produce earthquakes.

12. Chapter 8 Faults at Tectonic Plate Boundaries, continued
Section 1 What Are Earthquakes?
Faults at Tectonic Plate Boundaries, continued
Transform motion occurs where two plates slip past each other, creating strike-slip faults. Blocks of crust slide horizontally past each other.

13. Chapter 8 Faults at Tectonic Plate Boundaries, continued
Section 1 What Are Earthquakes?
Faults at Tectonic Plate Boundaries, continued
Convergent motion occurs where two plates push together, creating reverse faults. Blocks of crust that are pushed together slide along reverse faults.

14. Chapter 8 Faults at Tectonic Plate Boundaries, continued
Section 1 What Are Earthquakes?
Faults at Tectonic Plate Boundaries, continued
Divergent motion occurs where two plates pull away from each other, creating normal faults. Blocks of crust that are pulled away from each other slide along normal faults.

15. Chapter 8 Faults at Tectonic Plate Boundaries, continued
Section 1 What Are Earthquakes?
Faults at Tectonic Plate Boundaries, continued
Earthquake Zones Most earthquakes happen in the earthquake zones along tectonic plate boundaries. Earthquake zones are places where a large number of faults are located.
Not all faults are located at tectonic plate boundaries. Sometimes, earthquakes happen along faults in the middle of tectonic plates.

16. How Do Earthquake Waves Travel?
Chapter 8
Section 1 What Are Earthquakes?
How Do Earthquake Waves Travel?
Waves of energy that travel through the Earth away from an earthquake are called seismic waves.
Seismic waves that travel along the Earth’s surface are called surface waves.

17. Seismic Waves: Surface Waves
Chapter 8
Section 1 What Are Earthquakes?
Seismic Waves: Surface Waves
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Visual Concept

18. Chapter 8 How Do Earthquake Waves Travel?, continued
Section 1 What Are Earthquakes?
How Do Earthquake Waves Travel?, continued
Seismic waves that travel through Earth’s interior are called body waves. There are two types of body waves: P waves and S waves.
P waves are seismic waves that cause particles of rock to move in a back-and-forth direction.
S waves are seismic waves that cause particles of rock to move in a side-to-side direction.

19. Chapter 8
Section 1 What Are Earthquakes?

20. Bellringer Chapter 8 Create a qualitative scale for gauging earthquake
Section 2 Earthquake Measurement
Bellringer
Create a qualitative scale for gauging earthquake
intensity. Describe the effects of very minor earthquakes and extreme earthquakes.
What kind of damage would be done to buildings, water and power supplies, animals, forests, and people?

21. Objectives Chapter 8 Explain how earthquakes are detected.
Section 2 Earthquake Measurement
Objectives
Explain how earthquakes are detected.
Describe how to locate an earthquake’s epicenter.
Explain how the strength of an earthquake is measured.
Explain how the intensity of an earthquake is measured.

22. Locating Earthquakes Chapter 8
Section 2 Earthquake Measurement
Locating Earthquakes
Scientists use seismographs to study earthquakes.
A seismograph is an instrument that records vibrations in the ground and determines the location and strength of an earthquake.
When earthquake waves reach a seismograph, it creates a seismogram, a tracing of the earthquake’s motion.

23. Locating Earthquakes, continued
Chapter 8
Section 2 Earthquake Measurement
Locating Earthquakes, continued
Determining Time and Location of Earthquakes Seismograms are used to find an earthquake’s epicenter.
An epicenter is the point on the Earth’s surface directly above an earthquake’s starting point.

24. Locating Earthquakes, continued
Chapter 8
Section 2 Earthquake Measurement
Locating Earthquakes, continued
A focus is the point inside the Earth where an earthquake begins.
An earthquake’s epicenter is on the Earth’s surface directly above the earthquake’s focus.

25. Locating Earthquakes, continued
Chapter 8
Section 2 Earthquake Measurement
Locating Earthquakes, continued
The S-P Time Method is perhaps the simplest method by which seismologists find an earthquake’s epicenter.
This method is explained in the following Visual Concepts presentation.

26. S and P Time Method: Finding an Epicenter
Chapter 8
Section 2 Earthquake Measurement
S and P Time Method: Finding an Epicenter
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Visual Concept

27. Chapter 8 Measuring Earthquake Strength and Intensity
Section 2 Earthquake Measurement
Measuring Earthquake Strength and Intensity
The Richter Magnitude Scale Throughout much of the 20th century, seismologists used a scale created by Charles Richter to measure the strength of earthquakes.
Earthquake Ground Motion A measure of the strength of an earthquake is called magnitude. The Richter scale measures the ground motion from an earthquake and adjusts for distance to find its strength.

28. Richter Scale Chapter 8 Section 2 Earthquake Measurement
Click below to watch the Visual Concept.
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Visual Concept

29. Chapter 8 Measuring Earthquake Strength, continued
Section 2 Earthquake Measurement
Measuring Earthquake Strength, continued
Modified Mercalli Intensity Scale A measure of the degree to which an earthquake is felt by people and the damage it caused is called intensity.
Currently, seismologists use the Modified Mercalli Intensity Scale to measure earthquake intensity. This is a numerical scale that uses Roman numerals from I to XII to describe earthquake intensity levels.

30. Chapter 8 Measuring Earthquake Strength, continued
Section 2 Earthquake Measurement
Measuring Earthquake Strength, continued
In the Modified Mercalli Intensity Scale, an intensity of I describes an earthquake that is not felt by most people. An intensity level of XII indicates total damage of an area.
Because the effects of an earthquake vary based on location, any earthquake will have more than one intensity value. Intensity values usually are higher near the epicenter.

31. Chapter 8
Section 3 Earthquakes and Society
Bellringer
If you have ever experienced an earthquake, write a short paragraph describing how you felt and what you did to protect yourself during the quake. If you have not experienced an earthquake, write a paragraph describing what you think you would do during a moderate earthquake.
Do you know what to do in an earthquake, fire, tornado, or serious storm?

32. Chapter 8
Section 3 Earthquakes and Society
Objectives
Explain how earthquake-hazard level is determined.
Compare methods of earthquake forecasting.
Describe five ways to safeguard buildings against earthquakes.
Outline earthquake safety procedures.

33. Earthquake Hazard Chapter 8
Section 3 Earthquakes and Society
Earthquake Hazard
Earthquake hazard is a measurement of how likely an area is to have damaging earthquakes in the future.
An area’s earthquake-hazard level is determined by past and present seismic activity.
The greater the seismic activity, the higher the earthquake-hazard level.

34. Earthquake-Hazard Level
Chapter 8
Section 3 Earthquakes and Society
Earthquake-Hazard Level
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Visual Concept

35. Earthquake Forecasting
Chapter 8
Section 3 Earthquakes and Society
Earthquake Forecasting
Forecasting when and where earthquakes will occur and their strength is difficult.
By studying areas of seismic activity, seismologists have discovered some patterns in earthquakes that allow them to make some general predictions.

36. Earthquake Forecasting, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquake Forecasting, continued
Strength and Frequency Earthquakes vary in strength. The strength of earthquakes is related to how often they occur.
This table shows more detail about the relationship.

37. Earthquake Forecasting, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquake Forecasting, continued
Another method of forecasting an earthquake’s strength, location, and frequency is the gap hypothesis.
The gap hypothesis is based on the idea that a major earthquake is more likely to occur along the part of an active fault where no earthquakes have occurred for a certain period of time.

38. Earthquake Forecasting, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquake Forecasting, continued
An area along a fault where relatively few earth-quakes have occurred recently but where strong earthquakes have occurred in the past is called a seismic gap.

39. Earthquake Forecasting, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquake Forecasting, continued
Using the Gap Hypothesis Not all seismologists believe the gap hypothesis is an accurate method of forecasting earthquakes.
But some seismologists think the gap hypothesis helped forecast the approximate location and strength of the 1989 Loma Prieta earthquake in California.

40. Gap Hypothesis and Seismic Gaps
Chapter 8
Section 3 Earthquakes and Society
Gap Hypothesis and Seismic Gaps
Click below to watch the Visual Concept.
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Visual Concept

41. Earthquakes and Buildings
Chapter 8
Section 3 Earthquakes and Society
Earthquakes and Buildings
Earthquakes can easily topple buildings and destroy homes. Today, older structures in seismically active places, such as California, are being made more earthquake resistant.
Retrofitting is the name given to the process of making older structure more earthquake resistant.

42. Earthquakes and Buildings, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquakes and Buildings, continued
A common way of retrofitting an older home is to securely fasten it to its foundation.
Steel is often used to strengthen buildings and homes made of brick.

43. Earthquakes and Buildings, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquakes and Buildings, continued
Earthquake-Resistant Buildings A lot has been learned from building failure during earthquakes.
With this knowledge, architects and engineers use new technology to design and construct buildings and bridges to better withstand earthquakes.
The next slide shows some of the technology used to make earthquake-resistant buildings.

44. Earthquakes and Buildings, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquakes and Buildings, continued

45. Are You Prepared for an Earthquake?
Chapter 8
Section 3 Earthquakes and Society
Are You Prepared for an Earthquake?
Before the Shaking Starts The first thing should do safeguard your home against earthquakes.
Place heavier objects on lower shelves so they do not fall during an earthquake.
Find safe places within each room of your home and outside of your home.
Make a plan with others to meet in a safe place after the earthquake is over.

46. Earthquake Preparations, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquake Preparations, continued
When the Shaking Starts If you are indoors, crouch or lie face down under a table or desk.
If you are outside, cover your head with your hands and lie face down away from buildings, power lines, or trees.
If you are in a car on an open road, you should stop the car and remain inside.

47. Earthquake Preparations, continued
Chapter 8
Section 3 Earthquakes and Society
Earthquake Preparations, continued
After the Shaking Stops Try to calm down and get your bearings.
Remove yourself from immediate danger, such as downed power lines, broken glass, and fire hazards.
Do not enter any damaged buildings unless you are told it is safe by someone in authority.
Beware that aftershocks may cause more damage.

48. Chapter 8
Earthquakes
Concept Map
Use the terms below to complete the concept map on the next slide.
seismograph
seismic waves
earthquakes
surface waves
body waves
S waves

49. Chapter 8
Earthquakes

50. Chapter 8
Earthquakes

51. End of Chapter 8