1. Earthquakes

2. 1. What are Earthquakes?
The shaking or trembling caused by the sudden release of energy
Usually associated with faulting or breaking of rocks

3. Where Do Earthquakes Occur and How Often?
~80% of all earthquakes occur in the circum-Pacific belt
most of these result from convergent margin activity
~15% occur in the Mediterranean-Asiatic belt
remaining 5% occur in the interiors of plates and on spreading
ridge centers
more than 150,000 quakes strong enough to be felt are recorded
each year

4. 2. Earthquake Anatomy
The actual place underground where the rocks break producing vibrations is called the focus
The place on the surface directly above the focus is called the epicenter

5. 3. What causes Earthquakes?
A. Movement along faults: occurs when the energy exceeds the friction holding the sides of the fault together and is suddenly released. This is the Elastic Rebound Theory.
B. Movement of magma (volcanic)
C. Volcanic eruptions

6. What is the Elastic Rebound Theory?
Explains how energy is stored in rocks
Rocks bend until the strength of the rock is exceeded
Rupture occurs and the rocks quickly rebound to an undeformed shape
Energy is released in waves that radiate outward from the fault

7. 4. What types of forces are created?
A. Extension Force:
stretching or pulling force
Makes a normal fault

8. Normal Fault

9. 4. What types of forces are created?
B. Compression Force:
force pushing something together
Makes a reverse fault

10. Reverse Fault

12. 4. What types of forces are created?
C. Shear Force:
a system of forces that operates against a body from different sides
Makes a strike-slip fault

13. Strike-Slip Fault

14. Landscape Shifting, Wallace Creek
Source: John S. Shelton
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15. 5. Seismic Waves
Originate at the focus and travel outward in all directions
Foreshocks: small earthquakes that come before a major earthquake
Aftershocks: Are adjustments in the crust after an earthquake

16. 6. How do we Measure Earthquakes?
A. Earthquake waves are recorded by a seismograph and the recording of waves on paper is called seismogram

17. 6. How do we Measure Earthquakes?
B. Richter Scale: Measures the amplitude of earthquake waves on seismograms
Scale from 1-10
Each number is 10 times the amplitude of the number below

18. 7. Locating Earthquakes
After an earthquake, the difference in arrival times of seismic waves at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.

19. 7. Locating Earthquakes
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20. Map of Epicenter, KY, TN
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21. 8. Earthquake Dangers
A. Most injuries and deaths are caused by falling objects and most property damage results from fires that start

22. San Francisco, 1906

23. San Francisco, 1906

24. 8. Earthquake Dangers
B. Tsunami: seismic sea wave sometimes generated when an earthquake originates on the ocean floor

25. Generation of a Tsunami
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26. Tsunami—December 2004

27. NSF North Mississippi GK-8
Who Feels the Shaking?
The shaking starts at the epicenter and spreads in circles outward much like the ripples of water dripping into a puddle.
NSF North Mississippi GK-8

28. 8. Earthquake Dangers
C. Liquefaction: unconsolidated materials that are water saturated may turn to a fluid causing some underground objects such as storage tanks to float to the surface
Ground fissures caused by liquefaction near the mouth of the Pajaro River in California during the 1989 Loma Prieta earthquake. When the surface of the ground oscillates, wet, sandy, and muddy soils can flow like a liquid. This is liquefaction. You can liquefy wet sand at the beach by pumping it up and down with your feet. Photo courtesy of the Loma Prieta Collection, Earthquake Engineering Research Center, UC Berkeley.

29. Liquefaction
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30. Source: Steve McCutcheon/Alaska Pictorial Services
Liquefaction
Source: Steve McCutcheon/Alaska Pictorial Services
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31. Elevated Freeway Collapse in Kobe
Source: Hosaka Naoto/Gamma Liaison
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32. 8. Earthquake Dangers
D. Landslides

33. Earthquake Safety
Protect yourself from falling objects (GET UNDER SOMETHING) or stand in a hallway or doorway (watch out for a swinging door)
Do not try to go outside during the earthquake
After the earthquake and before the aftershocks, go outside
Do not return to the building until it has been inspected