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Earthquakes Lecture
 

Earthquakes Lecture

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    Earthquakes Lecture Earthquakes Lecture Presentation Transcript

    • Earthquakes Chapter 19
    • Earthquakes
      • Natural vibrations of ground caused by movement along fractures in Earth’s crust or by volcanic eruptions
    • Stress and Strain
      • Stress- forces per unit area exceed the strength of the rocks involved
        • Compression-Decreases Volume
        • Tension- Pulls material apart
        • Shear- Causes Twisting
      • Strain- Deformation of materials caused by stress
    • Faults- fracture of Earth’s crust
      • Reverse- Horizontal compression, Causes shortening, Foot wall goes down
    • Faults- Con’t
      • Normal- Horizontal tension, Causes extension, Foot wall goes up
    • Faults- Con’t
      • Strike-Slip- Horizontal Shear, causes offset
    •  
    • Waves
      • Primary- P- Pressure Wave
      • Secondary- S- Side-to-side wave
      • Surface Wave- L-Wave
      • Page 498
    • Location of Earthquakes
      • Focus- point where an earthquake originates
      • Epicenter- Place on Earth's surface where EQ occurred
    • Seismic Waves
      • Seismology- Study of Earthquake waves
      • Seismograph- instrument for recording earthquake waves
    • Waves
      • P wave- arrives 1 st
      • S wave- arrives 2nd
      • L wave- last and largest
    • Clues to Earth’s Interior
      • Seismic waves change speed and direction when they encounter different materials
        • P and S waves travel fairly straight through the mantle
        • P waves strike the core and are bent (11,000 Km from focus)
          • Re-emerge at 16,000 km from focus, after shadow
    • Clues to Earth’s Interior- Con’t
      • S-waves cannot travel through liquids so they can’t pass through the core (never beyond shadow)
      • P waves speed up through solids
    •  
    • Measuring and Locating EQ
      • Magnitude- amount of energy released
        • Richter Scale- size of largest seismic waves released by quake
          • Each # increase is a 10 fold increase in energy
          • Each increase in amplitude (height of wave) is a 32 time increase in energy
    • Measuring and Locating EQ- Con’t
      • Moment Magnitude Scale- uses size of fault rupture, amount of movement and rock’s stiffness
      • Modified Mercalli Scale- uses damage to buildings at location of worst damage
        • Uses I-XII Roman Numerals- Called Intensity
        • Measures Surface Waves
      • Depth of Focus- Deeper EQ usually less intense
    • Measuring and Locating EQ-Con’t
      • Locating EQ- time and location unknown
        • Distance determined by time between P wave and S wave--- AT 3 STATIONS
        • Time calculated using same P-S interval
    • Seismic Belts
      • Earthquakes not random
        • Ring of Fire- Edge of Pacific Plate- 80% of all Earthquakes
        • Mediterranean- Asian Belt- 15% of EQ
    •  
    • Earthquakes and Society
      • Earthquake Hazards
        • Structural failure
          • Ground floor fails -> Upper Floors Fail -> Pan caking
          • Height- 5-15 stories causes vibrations which are similar to natural sway; Shorter and taller buildings are different
        • Land/Soil Fracture
          • Landslides- Common in saturated areas
          • Soft ground conducts waves well -> more damage
        • Fault Scarps- vertical offsets -> waterfalls, road problems
    • Earthquakes and Society- Con’t
      • Tsunami- ocean waves created by EQ
        • Travels fast and are low (less than 4 feet high) in open ocean, but pile up hundreds of feet tall near shore
        • Ocean recedes dramatically before tsunami
    • Earthquake Risk
      • Here we have a 3% risk over 50 years
      • Hot Spot in US:
        • CA
        • Rocky Mountains
        • WA, OR
        • MO