Earthquakes how measureimpact
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Earthquakes how measureimpact Presentation Transcript

  • 1. Earthquakes: How do we measure their impact?
    8SCIENCE: Wed. April 6/Thurs. April 7
  • 2. Review: Forces and Faults
    What are 3 types of forces responsible for earthquakes?
    Compression
    Tension
    Shear
    What faults are associated with each type of force? Describe.
    Compression – reverse fault
    Tension – normal fault
    Shear – strike – slip fault
    Reverse
  • 3. Energy and Seismic Waves
    Seismic waves
    Created by the earthquake
    When rocks move and break along a fault, energy is released and this creates damage
    Energy is released from the focus, located under the surface of the Earth
    This energy travels away from the focus as seismic waves
  • 4. Seismic Waves
    Primary waves (P – waves)
    Make rocks vibrate back and forth
    Fastest waves at about 6km/second
    Secondary waves (S – waves)
    Shake rocks from side to side
    Half the speed of P waves about 3 km/second
    Energy that reaches the surface is in the form of waves called surface waves
    Cause the most damage but are the slowest
  • 5. Surface Waves
    The point on the Earth’s surface directly above an earthquake’s focus is the epicenter
    Surface wavestravel outward from the epicenter and move up, down and side to side
    Can cause buildings to move in different directions and fall apart
  • 6. How do we measure the strength of an earthquake?
    Scientists (seismologists) use the different speeds of the seismic waves to find the distance to the epicenter of the earthquake
    A seismograph measures the energy released, or magnitude of the earthquakes
    Which types of waves arrive first to a station?
    1)Primary2)Secondary3)Surface
  • 7. How do we measure the strength of an earthquake?
    Earthquake magnitude is usually measured using the Richter scale
    1.0 – 9.0
    Each 1 step increase = 10 x strongerEx: From 6.0 to 8.0 = 100x