1. Understanding Earth Chapter 13: EARTHQUAKES Grotzinger • Jordan
Seventh Edition
Chapter 13:
EARTHQUAKES
© 2014 by W. H. Freeman and Company

2. Chapter 13
Earthquakes

3. About Earthquakes
Earthquakes can be understood in terms of the basic mechanisms of deformation.
Most earthquakes occur at plate boundaries (convergent, divergent, and sliding).
Earthquakes cannot yet be reliably predicted or mitigated.

4. Lecture Outline What is an earthquake? 2. How do we study earthquakes?
3. Earthquakes and patterns of faulting
4. Earthquake hazards and risks
5. Can earthquakes be predicted?

5. ● Global forces at work ● stress ● strain ● strength
1. What Is an Earthquake?
● Global forces at work
● stress
● strain
● strength

7. 1. What Is an Earthquake?
● Earthquakes occur where rocks being stressed suddenly break along a new or pre-existing fault.
● Seismic waves are ground vibrations caused by rocks slipping along opposite sides of a fault.

9. ● Why earthquakes occur ● elastic rebound theory ● fault rupture
1. What Is an Earthquake?
● Why earthquakes occur
● elastic rebound theory
● fault rupture
● epicenter
● focus

11. Example of Elastic Rebound
1. What Is an Earthquake?
Example of Elastic Rebound

12. 1. What Is an Earthquake? Fault Rupture

13. ● Local buildup and release of stress ● foreshock ● aftershock
1. What Is an Earthquake?
● Local buildup and release of stress
● foreshock
● aftershock

15. ● Seismographs are machines that record the seismic waves
2. How Do We Study Earthquakes?
● Seismographs are machines that
record the seismic waves
generated by earthquakes.
● vertical ground movements
● horizontal ground movements

19. ● P waves (primary waves) ● S waves (secondary waves) ● Surface waves
2. How Do We Study Earthquakes?
● Seismic wave types
● P waves (primary waves)
● S waves (secondary waves)
● Surface waves

22. ● Locating the earthquake epicenter ● P- and S-wave arrival times
2. How Do We Study Earthquakes?
● Locating the earthquake epicenter
● P- and S-wave arrival times
from at least three
seismographs
● Graph of distance traveled
versus time elapsed

26. Determining Richter magnitude
2. How Do We Study Earthquakes?
Determining Richter magnitude

27. ● Measuring the size of an earthquake ● Richter magnitude
2. How Do We Study Earthquakes?
● Measuring the size of an earthquake
● Richter magnitude
● Moment magnitude
● Shaking intensity

28. ● Magnitude and frequency ● many small earthquakes
2. How Do We Study Earthquakes?
● Magnitude and frequency
● many small earthquakes
● few large earthquakes

29. Relationship between magnitude and energy release
2. How Do We Study Earthquakes?
Relationship between magnitude and energy release

30. Modified Mercalli Intensity Scale
2. How Do We Study Earthquakes?
Modified Mercalli Intensity Scale

31. Mercalli
intensity
of the
New Madrid
earthquake,
Dec. 16, 1811

32. ● Determining fault mechanisms from earthquake data
2. How Do We Study Earthquakes?
● Determining fault mechanisms from
earthquake data
● pattern of ground shaking
(first motion of P waves)
● orientation of fault rupture
● direction of slip

33. ● Fault mechanism tells us whether the rupture was: ● normal ● reverse
2. How Do We Study Earthquakes?
● Fault mechanism tells us whether
the rupture was:
● normal
● reverse
● strike-slip (right- or left-lateral)

34. Main Types of Fault Movement
2. How Do We Study Earthquakes?
Main Types of Fault Movement

39. 2. How Do We Study Earthquakes?
First Motion of P Waves

40. ● GPS measurements of “silent” earthquakes: ● creep events
2. How Do We Study Earthquakes?
● GPS measurements of “silent”
earthquakes:
● creep events
● continuous creep

41. ● Earthquakes and plate tectonics ● divergent boundaries
3. Earthquakes and Patterns of Faulting
● Earthquakes and plate tectonics
● divergent boundaries
● transform-fault boundaries
● convergent boundaries
● intraplate earthquakes

42. 3. Earthquakes and Patterns of Faulting

43. 3. Earthquakes and Patterns of Faulting

44. Example: Fault system of southern California
3. Earthquakes and Patterns of Faulting: Regional Fault Systems
Example: Fault system of southern California

46. ● Earthquakes and destruction ● loss of life ● property damage
3. Earthquakes and Patterns of Faulting
● Earthquakes and destruction
● loss of life
● property damage
● tsunami and landslides

47. Thought questions for this chapter
The belts of shallow-focus earthquakes, shown by the blue dots in Figure 13-15a, are wider and more diffuse in the continents than in the oceans. Why?
Why are earthquakes with focal depths greater than 20 km infrequent in continental lithosphere?
Why do the largest earthquakes occur on megathrusts at subduction zones and not, say, on continental strike-slip faults?
How big would a fault have to be to produce a magnitude-10 earthquake? Do you think that such a large earthquake could occur by the rupturing of subduction-zone megathrusts?

48. Thought questions for this chapter
In Figure 13-3, the right-lateral fault offsets the fence line to the right. In Figure 13-17, the mid-ocean ridge crest is also offset to the right. Why then is the transform fault in Figure left-lateral?

49. ● How earthquakes cause damage ● faulting and shaking
4. Earthquake Hazards and Risks
● How earthquakes cause damage
● faulting and shaking
● landslides and ground failures
● tsunamis
● fires

50. Shaking damage in
Los Angeles, 1994

51. Shaking damage in
Kobe, Japan, 1995

52. Shaking damage in
Haiti, 2010

53. Ground failure damage
in Alaska, 1964

54. Tsunami effects in
Thailand, 2004

55. Tsunami effects in
Japan, 2011

56. 4. Earthquake Hazards and Risks

57. ● Reducing earthquake risks ● hazard characterization
4. Earthquake Hazards and Risks
● Reducing earthquake risks
● hazard characterization
● land-use policies
● earthquake engineering
(including building codes)
● emergency preparedness

58. Example of
hazard
characterization:
Seismic
hazard map
of the U.S.

59. Example of
hazard
characterization:
Seismic
hazard risk
of the U.S.

60. Example of
poor land-use
planning:
Construction
along the trace
of the
San Andreas
fault zone,
San Francisco

61. 4. Earthquake Hazards and Risks: Emergency Preparedness

62. ● Reducing earthquake risks ● earthquake early warning systems
4. Earthquake Hazards and Risks
● Reducing earthquake risks
● earthquake early warning
systems
● tsunami warning systems

63. 4. Earthquake Hazards and Risks: World Seismic Hazard Map

64. Thought questions for this chapter
Would you support legislation to prevent owners from building structures close to active faults?

65. ● Earthquake forecasting ● long-term ● medium-term ● short-term
5. Can Earthquakes Be Predicted?
● Earthquake forecasting
● long-term
● medium-term
● short-term

66. Thought questions for this chapter
Taking into account the possibility of false alarms, reduction of casualties, mass hysteria, economic depression, and other possible consequences of earthquake prediction, do you think the objective of predicting earthquakes should have a high priority?

67. Key terms and concepts Building code Earthquake Elastic rebound theory
Aftershock
Building code
Earthquake
Elastic rebound theory
Epicenter
Fault mechanism
Fault slip
Focus
Foreshock
Intensity scale
Magnitude scale
P wave
Recurrence interval
S wave
Seismic hazard

68. Key terms and concepts
Seismic risk
Seismograph
Surface wave
Tsunami