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Earthquakes

Earthquakes. An Earthquake is the sudden movement of the earth. It is caused by the abrupt release of strain that has accumulated over a long time. Earthquakes in History. Horses killed by a collapsing wall - San Francisco Earthquake 1906. San Francisco - 1906. Anchorage, Alaska - 1964.

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Earthquakes

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  1. Earthquakes

  2. An Earthquake is the sudden movement of the earth • It is caused by the abrupt release of strain that has accumulated over a long time

  3. Earthquakes in History Horses killed by a collapsing wall - San Francisco Earthquake 1906

  4. San Francisco - 1906

  5. Anchorage, Alaska - 1964

  6. Where Earthquakes Occur

  7. Where Earthquakes Occur • Most Earthquakes occur at the boundaries where tectonic plates meet

  8. Where Earthquakes Occur

  9. How Earthquakes Happen • The crust may first bend, and then when stress exceeds the strength of the rocks, break and “snap” to a new position. • In the process, vibrations called “seismic waves” are generated.

  10. Seismic Waves

  11. Three Types of Faults Strike-Slip Thrust Normal

  12. Strike-slip Fault Example

  13. Strike-slip Fault Example 1906 San Francisco Earthquake

  14. Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake December 16, 1954

  15. Thrust Fault Example

  16. Severity of an Earthquake • The severity of an earthquake can be expressed in several ways:

  17. Magnitude • The measure of the amplitude of seismic waves • Expressed by the Richter Scale • Richter Earthquake Magnitudes Effects • Less than 3.5 Generally not felt, but recorded. • 3.5-5.4 Often felt, but rarely causes damage. • Under 6.0 At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions. • 6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live. • 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. • 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

  18. Magnitude – Richter Scale Scale about 3.0 Scale about 6.0 Scale about 9.0

  19. Intensity • A subjective measure that describes how strong a shock was felt at a particular location • Expressed by the Modified Mercalli Scale

  20. What Controls the Level of Shaking? • Magnitude • More energy released • Distance • Shaking decays with distance • Local soils • amplify the shaking

  21. Earthquake Effects - Ground Shaking Northridge, CA 1994

  22. Earthquake Effects - Ground Shaking

  23. Earthquake Effects - Ground Shaking KGO-TV News ABC-7 Loma Prieta, CA 1989

  24. Earthquake Effects - Ground Shaking Kobe, Japan 1995

  25. Earthquake Effects - Ground Shaking Kobe, Japan 1995

  26. Earthquake Effects - Surface Faulting Landers, CA 1992

  27. Earthquake Effects - Liquefaction Source: National Geophysical Data Center Niigata, Japan 1964

  28. Earthquake Effects - Landslides Turnnagin Heights,Alaska,1964

  29. Earthquake Effects - Fires Loma Prieta, CA 1989

  30. Earthquake Effects - Tsunamis 1957 Aleutian Tsunami

  31. Earthquake Effects - Tsunamis Sumatra –Andaman Earthquake/Tsunami BEFORE

  32. Earthquake Effects - Tsunamis

  33. Earthquake Effects - Tsunamis Sumatra –Andaman Earthquake/Tsunami AFTER

  34. Earthquake Effects - Tsunamis Sumatra –Andaman Earthquake/Tsunami AFTER

  35. Pacific-North American Plate Boundary

  36. The San Andreas Fault

  37. Did You Feel It? http://earthquake.usgs.gov

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