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


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  • 1. 9 th Grade Chapter 8 Lesson 2 Pgs. 203-212 For student Use Only
  • 2. 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
  • 3. 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
  • 4. 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
  • 5. 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
  • 6. 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
  • 7. 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
  • 8. 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.
  • 9. 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
  • 10. 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)
  • 11. 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
  • 12. 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
  • 13. 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
  • 14. 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