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EARTHQUAKES
PowerPoint Presentation Outline Notes
What Is An Earthquake?
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A wave-like vibration
Travels away from a point of sudden energy release
Focus is the point of sudden energy release
Epicenter is located at the earth’s surface immediately above the focus
What Causes Earthquakes?
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Most earthquakes are caused by faults
Volcanoes
Atomic explosions
Elastic Rebound Theory
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1906 earthquake
Strain built up along strike-slip fault
Earthquakes - sudden release of energy
Called elastic rebound theory
Horizontal slippage
Some faults are locked
Where Do Earthquakes Occur?
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Most earthquakes occur in linear belts
80% occur around the Pacific Ocean Basin
Plate boundaries
Bay Area Faults
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San Andreas transform fault
Two plates grind past each other
Many branches off this fault system
o Hayward
o Rodgers Creek
o Calaveras
o Green Valley
Potential For Bay Area Earthquakes
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Are we overdue for an earthquake?
67-70% risk in 30 years
Which Parts Of The United States Are Vulnerable To Earthquakes?
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Southwest including California
Pacific Northwest
Yellowstone Area
How Are Seismic Waves Recorded?
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Seismographs record seismic waves
Pen stays relatively still due to inertia of heavy mass
Rotating drum moves with the ground vibration
Seismic Waves
Body waves move through the earth’s interior
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P (primary) waves move fastest
o Compressional
S (shear) waves move more slowly
o Shake up and down
Seismograms Record Vibrations
30. P Waves
31. S Waves
32. L or Surface Waves travel slowly
o Most dangerous
Seismograms Locate Epicenters
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Difference in arrival time between P and S waves can determine
distance from epicenter
Three or more stations are needed to determine the epicenter
How Are Earthquakes Measured?
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Richter scale measures the magnitude of energy released at the focus
o Open-ended scale - logarithmic increase
o Richter 3 to Richter 4 is 30 X
Modified Mercalli scale measures the intensity of an earthquake
according to damage observed
o Scale I-XII
What Determines the Amount of Damage in an Earthquake?
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Magnitude and duration of the earthquake
Underlying geology
Building construction
Effects of Earthquakes
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Ground Shaking
Fault Rupture and Uplift
Liquefaction
Dam Breaks
Landslides
Tsunami
Aftershocks
Fire
Where is the Safest Place to Live?
Liquefaction
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Loose sand and mud turns into quicksand as groundwater rises
Heavy objects sink in and light objects pop out
Bayfill such as Emeryville and Alameda South Shore is vulnerable
What Causes a Tsunami?
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Movement of the ocean floor
Why Is a Tsunami Dangerous?
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A tsunami travels at over 800 kmh in open water
Slows down and piles higher and higher in shallow water
30 meter high waves swamp the coast