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1. What are Earthquakes?
• The shaking or trembling caused by the sudden release of energy
• Usually associated with faulting or breaking of rocks
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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
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o The actual place underground where the rocks break producing vibrations is called the focus
o The place on the surface directly above the focus is called the epicenter
2. Earthquake Anatomy
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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
3. What causes Earthquakes?
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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
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A. Extension ForceA. Extension Force: stretching or pulling force Makes a normal fault
4. What types of 4. What types of forces forces are created?
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http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
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B. Compression ForceB. Compression Force: force pushing something
togethertogether Makes a reverse fault
4. What types of 4. What types of forcesforces are created?
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http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
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C. Shear ForceC. Shear Force: a system of forces
that operates against a body from different sides
Makes a strike-slip fault
4. What types of 4. What types of forcesforces are created?
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http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
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Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–14
Landscape Shifting, Wallace Creek
Source: John S. Shelton
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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
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6. How do we Measure Earthquakes?
A. Earthquake waves are recorded by a seismograph and the recording of waves on paper is called seismogram
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B. Richter ScaleB. 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
6. How do we Measure Earthquakes?
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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.
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Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–20
7. Locating Earthquakes
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Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–21
Map of Epicenter, KY, TN
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8. Earthquake Dangers
o A. Most injuries and deaths are caused by falling objects and most property damage results from fires that start
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San Francisco, 1906
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San Francisco, 1906
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8. Earthquake Dangers
B. B. Tsunami: seismic sea wave sometimes generated when an earthquake originates on the ocean floor
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Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–26
Generation of a Tsunami
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Tsunami—December 2004
http://www.bedford.k12.ny.us:16080/flhs/science/images/tsunami2004/
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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.
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C. 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
8. Earthquake Dangers
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.
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Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–30
Liquefaction
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Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–31
Liquefaction
Source: Steve McCutcheon/Alaska Pictorial Services
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Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–32
Elevated Freeway Collapse in Kobe
Source: Hosaka Naoto/Gamma Liaison
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D. D. Landslides
8. Earthquake Dangers
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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