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EARTHQUAKES. What is an Earthquake?. Sudden movement in the Earth’s crust that releases energy as vibrations, or waves . Movement occurs along areas of weakness in the earth’s crust Elastic Rebound Theory – tension or stress, elastic displacement, release. Elastic Rebound.

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Presentation Transcript
what is an earthquake
What is an Earthquake?
  • Sudden movement in the Earth’s crust that releases energy as vibrations, or waves.
  • Movement occurs along areas of weakness in the earth’s crust
  • Elastic Rebound Theory – tension or stress, elastic displacement, release
slide6

Place on earth’s surface directly above the focus

Location where the actual slippage or

displacement occurs

Crack in the crust along

which movement occurs

how is energy transmitted
How is energy transmitted?
  • Energy is transmitted through seismic (earthquake) waves or vibrations
  • Types of earthquake waves:
      • P- waves: Primary waves
        • Travel fastest, arrive first
      • S- waves: Secondary waves
        • Travel more slowly than p-waves, arrive after P-wave
wave propagation transmission
Wave Propagation (transmission)
  • Longitudinal:
    • Particles move parallel to the direction wave travels
primary waves p waves
Primary waves (p-waves)
  • Longitudinal wave
  • Make the ground vibrate back and forth
  • Arrive at seismic recording stations first
  • Can travel through solids, liquids and gases (Solids and Fluids)
slide10
Transverse waves
    • Particles move perpendicular to direction of wave motion
secondary waves s waves
Secondary waves (s-waves)
  • Transverse wave
  • Travel about ½ as fast as p-waves
  • Make the ground vibrate from side to side, up and down
  • Can only travel through solids ONLY
slide14

in the samemedium, P waves travel at a greater velocity (speed) than S waves. However, the velocities of seismic waves depend upon the physical properties of the material through which the waves travel (medium). Higher density media result in a higher velocity of wave propagation.

Velocities:

types of seismic waves
Types of Seismic Waves
  • Body waves: travel through the earth
    • P-waves
    • S-waves
  • Surface waves:
    • Form when p and s waves reach the surface
    • Move slowly
    • Cause the most damage
how are earthquakes detected
How are earthquakes detected?

Seismograph:

  • an instrument attached to the Earth designed to detect crustal shifts

Seismogram:

  • recording of the earthquake waves by the Seismograph machine
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Mount St. Helens, Washington Seismogram, Station CPW, May 18, 1980 (located 70 miles northwest)

how is the strength of an earthquake measured
How is the strength of an earthquake measured?
  • Mercalli scale (un-scientific):
    • Based upon reports from people in affected area including damage and what was felt
    • Also known as Mercalli Intensity
  • Richter Magnitude Scale:
    • Measured using the wave size on seismogram
    • Magnitude scale (ex. An earthquake of 5 has 10 times as much energy released as a 4)
slide26

Indian Ocean December 26 , 2004 9.0

Off the coast of Honshu, Japan March 12, 2011 9.0

tsunami
Tsunami
  • Large wavelength wave produced by strong underwater earthquakes in the oceanic crust.
  • As wave approaches shore the height grows and can produce 30 m waves in extreme cases.
recent footage
Recent Footage:

Miyako Surge – coastal fishing city

Miyagi Surge – 6 miles inland

Miyagi Coast

4. Before and after aerial slides

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