Earthquake basics for a GE-level course in natural disasters.

1. Earthquakes

2. What is an Earthquake?

3. Elastic Rebound

4. Stress vs. Time
Stress

7. Epicenter vs. Focus

8. Types of Seismic Waves
Body Waves
Surface Waves

9. Primary (P) Waves
•Longitudinal (forward) motion
•Move by compression & expansion
•Fastest of the wave types
•Travel through solids & liquids

10. Secondary (S) Waves
•Shear (sideways) motion
•Move by lateral displacement
•Second fastest of the wave types
•Travel through solids only

11. Love (L) Waves
•Shear (sideways) motion
•Move by lateral displacement
•Second slowest of the wave types
•Travel through solids only

12. Rayleigh (R) Waves
•Elliptical motion
•Move by rotational displacement
•Slowest of the wave types
•Travel through solids and liquids

14. Where Do Earthquakes Occur?

16. Plate Boundaries
From Tarbuck and Lutgens
Divergent
Transform
Convergent

18. Benioff Zones

19. Types of Movement
Divergent Plate
Boundary
Convergent Plate
Boundary
Transform Plate
Boundary

20. Faults
Faults are fractures along which there has been vertical and/or
horizontal movement.

21. Normal
Reverse
Types of Faults
Strike-slip
Faults are classified by the relative direction of movement of the
rocks on either side with respect to each other side.

22. Normal Faults
Normal faults form as a result of tension. The hanging wall
moves downward with respect to the footwall. They are
referred to as normal because they appear to have “slipped” in
response to gravitational forces.

30. Mountain and Valley Topography
A characteristic of normal faulting in highly extensional
terrains, such as continental divergent plate boundaries, is that
of alternating mountain ranges (horsts) and valleys (grabens).

33. Reverse Faults
Reverse faults form as a result of compression. The hanging
wall moves upward with respect to the footwall. They are
referred to as reverse because they demonstrate the opposite
motion of normal faults.

35. Thrust Faults
Thrust faults are reverse faults with a low dip angle. They are
often associated with folding and are typically found in
association with convergent plate boundaries.

37. Strike-slip Faults
Strike-slip faults form as a result of lateral shearing. The two
sides of the fault move laterally past one another.

40. Methods of Measurement
Richter Scale Mercalli Scale
Charles Richter Giuseppe Mercalli
•Measures energy released
•Determined by wave amplitude
•Measures “intensity”
•Determined by degree of damage
We now use the “moment magnitude Now referred to as the modified Mercalli Scale

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The largest recorded earthquakes: Chile, 1960 – 8.3 on the Richter Scale, Mw= 9.5
Alaska, 1964 – 8.4 on the Richter Scale, Mw= 9.2
For each unit-increase in magnitude: Ground Shaking increases by a power of 10 (10x)
Energy released increases by a power of 30 (30x)

47. Largest Earthquakes in the World Since 1900
Location Date UTC Magnitude Coordinates
1. Chile 1960 05 22 9.5 38.24 S 73.05 W
2. Prince William Sound, Alaska 1964 03 28 9.2 61.02 N 147.65 W
3. Andreanof Islands, Alaska 1957 03 09 9.1 51.56 N 175.39 W
4. Kamchatka 1952 11 04 9.0 52.76 N 160.06 E
5. Off the West Coast of Northern Sumatra 2004 12 26 9.0* 3.30 N 95.78 E
6. Off the Coast of Ecuador 1906 01 31 8.8 1.0 N 81.5 W
7. Rat Islands, Alaska 1965 02 04 8.7 51.21 N 178.50 E
8. Assam - Tibet 1950 08 15 8.6 28.5 N 96.5 E
9. Kamchatka 1923 02 03 8.5 54.0 N 161.0 E
10. Banda Sea, Indonesia 1938 02 01 8.5 5.05 S 131.62 E
11. Kuril Islands 1963 10 13 8.5 44.9 N 149.6 E
*now 9.3

48. Table 4-1, p. 87
(possibly 750,000)

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55. Earthquake Destruction
Intensity map for the
1886 Charleston
Earthquake
Earthquake destruction takes a variety of forms, depending upon
geological setting, strength of the quake, and the nature of construction.

57. U.S. Earthquake Risk

59. Ground Rupture

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64. Ground Shaking
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68. Liquifaction
Japan 1964

69. Mexico City 1985

70. Indirect Damage

71. San Francisco
1999

72. Landslides
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73. Landslides (slumping)
Alaska 1964 Alaska 1964

74. Tsunamis

80. Historical Records
Plotting of historical earthquakes (location and size) can be used to
predict the degree of likely hazard for a given area.

81. Geologic History
Trenching and drilling along and across a fault can give us an idea of
how often and how frequently it has moved in the past.
Video 11:38 – 15:32

82. Seismic Gaps

83. Stress vs. Time
Stress

84. M 9.1
Dec. 2004
M 8.8
Feb. 2010
M 7.0
Jan. 2010
M 8.1
Sep. 2009
M 9.0
Mar. 2011

85. Fault Asperity

86. Characterisic Quakes
1910 AD
200 AD

88. Earthquake Frequency
USGS PAGERCAT 1900-2008, USGS-NEIC & gCMT 2008-present
Plot of number of earthquakes M7.5 and larger since 1900.

89. Fore- and Aftershocks
Timing and magnitude of earthquakes for Tohoku, Japan.

90. Mitigation

92. p. 105c

93. Fig. 4-40, p. 101
Base Isolators

94. p. 105b

95. p. 105a

96. p. 105d

98. Tsunami Detection
Video 24:19 – 35:23