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9th Grade Chapter 8 Lesson 2
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9th Grade Chapter 8 Lesson 2



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    9th Grade Chapter 8 Lesson 2 9th Grade Chapter 8 Lesson 2 Presentation Transcript

    • 9 th Grade Chapter 8 Lesson 2 Pgs. 203-212 For student Use Only
    • Earthquakes
      • Earthquake:
        • Any vibration (trembling or shaking) of the earth’s crust
        • Tremors: weak earthquake
      • Vibrations move through the ground like ocean waves
      • Earthquakes result from a sudden break in the rocks
    • Earthquakes
      • Earthquakes:
        • Even the largest earthquakes only last one minute, but can cause massive damage
          • Buildings, bridges, overpasses can collapse and rocks and earth can be moved
          • Aftershocks: smaller earthquakes or tremors accompany earthquakes
    • Earthquakes
      • Seismology: Study of earthquakes
        • Earthquakes follow the same natural laws
        • Tectonic Plates are the primary cause of the earthquakes (sudden movement of rock along a fault)
        • Faulting: involves vertical or horizontal movement of the plates
    • Earthquakes
      • Earthquakes:
        • The rocks grind together because they are jagged
        • The rocks get stuck
        • The rocks slip and release massive amounts of energy
        • Elastic Rebound Theory: rocks spring back to a position of little or no strain
    • Earthquakes
      • In an earthquake:
        • Rocks on one side of fault can be higher than on the other side of the fault
          • This is called a fault scarp
          • This happens along a strike-slip fault
          • Slickenslides are smooth fault scarps
            • San Andres Fault is a strike-slip fault
    • Earthquakes
      • Earthquakes begin below the ground, but appear on the surface
        • Focus: the point below the earth where the earthquake begins
        • Epicenter: point directly above the focus on the earth’s surface
    • Earthquakes
      • Shallow Focus Earthquakes:
        • 85% of earthquakes originate 5-40 mi. below the surface
      • Intermediate Focus Earthquakes:
        • 12% of earthquakes occur at depths of 40-200 mi.
      • Deep Focus Earthquakes:
        • 3% of earthquakes occur at depths of below 200 mi.
    • Earthquakes
      • Earthquake Waves:
        • P waves: primary waves, push and pull motion (up and down)
        • S waves: secondary waves, side to side motion
        • Surface Waves: These are a combination of P and S waves and act like ocean waves
    • Earthquake
      • Waves are measured by a seismograph
        • Seismograph measures P and S waves
          • P waves travel fastest
          • S waves arrive next
          • Surface waves come last
        • Seismographs can be used to detect where earthquakes are but there must be three points (This is called triangulation)
    • Earthquakes
      • Earthquake Zones:
        • Earthquakes occur everywhere, however, most occur in narrow areas
        • Circum-Pacific belt:
          • 80% of earthquakes
        • Mediterranean-Trans-Asiatic belt:
          • 15% of earthquakes
        • Mid-ocean ridges:
          • 5% of all earthquakes
    • Earthquakes
      • Earthquake Ratings:
        • Mercalli Scale:
          • Based on how it affects structures
          • Does not measure energy
          • Rates 1-12
        • Richter Scale
          • Measures power of Earthquake
          • Scale from 1-10
          • Each step is 250 times more powerful
    • Earthquakes
      • Earthquake Waves Teach Us:
        • Waves travel differently from different substances
        • They use this information as they study the structure of the Earth
        • Use artificial waves to find oil, use waves to spy on nuclear testing
    • Earthquakes
      • Earthquake Damage:
        • Most deaths come from falling buildings
        • Engineers design building codes to help reduce damage
        • Build on solid bedrock vs. sand
          • Sand is very unstable