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Faults and Earthquakes

Faults and Earthquakes . Some Important Earthquakes . 1755 - Lisbon, Portugal Killed 70,000, Raised Waves in Lakes all over Europe First Scientifically Studied Earthquake 1811-1812 - New Madrid, Missouri Felt over 2/3 of the U.S. Few Casualties 1886 - Charleston, South Carolina

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Faults and Earthquakes

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  1. Faults and Earthquakes

  2. Some Important Earthquakes 1755 - Lisbon, Portugal • Killed 70,000, Raised Waves in Lakes all over Europe • First Scientifically Studied Earthquake 1811-1812 - New Madrid, Missouri • Felt over 2/3 of the U.S. • Few Casualties 1886 - Charleston, South Carolina • Felt All over East Coast, Killed Several Hundred. • First Widely-known U.S. Earthquake 1906 - San Francisco • Killed 500 (later studies, possibly 2,500) • First Revealed Importance of Faults

  3. Some Important Earthquakes 1923 – Tokyo - Killed 140,000 in firestorm 1964 - Alaska • Killed about 200 • Wrecked Anchorage. • Tsunamis on West Coast. 1976 - Tangshan, China • Hit an Urban Area of Ten Million People • Killed 650,000 2003 – Indian Ocean • Worst Tsunami disaster in history • Killed 300,000 people

  4. How Seismographs Work

  5. Seismic Waves

  6. Locating Earthquakes

  7. Locating Earthquakes

  8. Locating Earthquakes

  9. Elastic Rebound

  10. Types of Faults Faults Are Classified According to the Kind of Motion That Occurs on Them • Joints - No Movement • Strike-Slip - Horizontal Motion • Dip-Slip - Vertical Motion

  11. Joints, Marathon County

  12. Columnar Jointing, Devil’s Postpile, California

  13. Joints, Door County

  14. Front Range Fault, Colorado

  15. Sierra Nevada, Manzanar, California

  16. Owens Valley, California

  17. Horsts and Grabens, California

  18. Horsts and Grabens, California

  19. San Andreas Fault, California

  20. Fault Gouge, San Andreas Fault

  21. San Andreas Fault, San Bernardino, California

  22. San Andreas Fault, California

  23. San Andreas Fault, Cajon Pass, California

  24. Epicenter and Focus Focus • Location within the earth where fault rupture actually occurs Epicenter • Location on the surface above the focus

  25. Major Hazards of Earthquakes • Building Collapse • Landslides • Fire • Tsunamis (Not Tidal Waves!)

  26. Safest & Most Dangerous Buildings • Small, Wood-frame House - Safest • Steel-Frame • Reinforced Concrete • Unreinforced Masonry • Adobe - Most Dangerous

  27. California Earthquakes … Then …

  28. …And Now

  29. Rebar in Freeway, California

  30. Tsunamis Probably Caused by Submarine Landslides Travel about 400 M.p.h. Pass Unnoticed at Sea, Cause Damage on Shore Warning Network Around Pacific Can Forecast Arrival Whether or Not Damage Occurs Depends on: • Direction of Travel • Harbor Shape • Bottom • Tide & Weather

  31. Tsunamis

  32. Magnitude and Intensity Intensity • How Strong Earthquake Feels to Observer Magnitude • Related to Energy Release • Determined from Seismic Records • Rough correlation between the two for shallow earthquakes

  33. Intensity How Strong Earthquake Feels to Observer Depends On: • Distance to Quake • Geology • Type of Building • Observer! Varies from Place to Place • Mercalli Scale- 1 to 12

  34. Intensity and Bedrock Depth in San Francisco, 1906

  35. Magnitude - Determined from Seismic Records Richter Scale: • Related to Energy Release • Exponential • No Upper or Lower Bounds • Largest Quakes about Mag. 8.7 • Magnitude-Energy Relation • 4 - 1 • 5 - 30 • 6 - 900: • 1 Megaton = about 7 • 7 - 27,000 • 8 - 810,000

  36. Seismic - Moment Magnitude A Seismograph Measures Ground Motion at One Instant But -- • A Really Great Earthquake Lasts Minutes • Releases Energy over Hundreds of Kilometers • Need to Sum Energy of Entire Record • Modifies Richter Scale, doesn't replace it • Adds about 1 Mag. To 8+ Quakes

  37. Are Earthquakes Getting More Frequent?

  38. Seismology and Earth's Interior Successive Approximation in Action

  39. 1. Assume the Earth is uniform. • We know it isn't, but it's a useful place to start.

  40. 2. Actual seismic signals don't match the predictions • If we match the arrival times of nearby signals, distant signals arrive too soon • If we match the arrival times of distant signals, nearby signals arrive too late. • Signals are interrupted beyond about 109 degrees

  41. 3. We conclude: • Distant signals travel through deeper parts of the Earth, therefore .. • Seismic waves travel faster through deeper parts of the Earth, and .. • They travel curving paths (refract) • Also, there is an obstacle in the center (the core).

  42. Waves Travel The Fastest Path

  43. Seismic Waves in the Earth

  44. Inner Structure of the Earth

  45. The overall structure of the Earth

  46. Strategies of Earthquake Prediction Lengthen Historical Data Base • Historical Records • Paleoseismology Short-term Prediction • Precursors Long-term Prediction • Seismic Gaps • Risk Levels Modeling • Dilatancy - Diffusion • Stick - Slip • Asperities • Crack Propagation

  47. Seismic Gaps

  48. A Strategy That Just Didn’t Work:Cienega Winery, Hollister, CA

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