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Earthquakes

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Earthquakes Earthquakes Earthquakes are natural vibrations of the ground, caused by: Fractures in earth s crust Volcanic eruptions Stress and Strain Stress causes ... – PowerPoint PPT presentation

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Title: Earthquakes


1
Earthquakes
2
Earthquakes
  • Earthquakes are natural vibrations of the ground,
    caused by
  • Fractures in earths crust
  • Volcanic eruptions

3
Stress and Strain
  • Stress causes fractures in rock
  • Three types of stress
  • Compression
  • Tension
  • Shear
  • Deformation caused by stress is known as strain

4
Compression
  • Compression is stress that decreases the volume
    of material

5
Tension
  • Tension is stress that pulls a material apart

6
Shear
  • Shear is stress that causes a material to twist

7
Effects of Strain and Stress
  • Stress and strain can cause deformation
  • Low stresses cause elastic strain
  • Elastic strain causes a material to bend and
    stretch
  • Can return to normal, like a rubber band
  • High stresses cause ductile deformation
  • Material is permanently deformed
  • Can cause breaks or failure

8
Faults
  • When stress causes rock to fail, a fault occurs
  • Fault Fracture(s) along which movement occurs
  • Three main types of faults
  • Reverse
  • Normal
  • Strike-Slip (Transform)

9
Reverse Fault
  • Reverse Faults are fractures that result from
    horizontal compression
  • Shortens crust horizontally

10
Normal Fault
  • Normal Faults are fractures caused by horizontal
    tension
  • Lengthens crust horizontally

11
Strike-Slip Fault
  • Strike-Slip Faults are fractures caused by
    horizontal shear
  • Motion is mainly horizontal

12
Earthquake Waves
  • Vibrations of the ground during earthquakes are
    called Seismic Waves
  • Three types
  • Primary Wave (P-Wave)
  • Secondary Wave (S-Wave)
  • Surface Waves

13
P-Waves
  • P-Waves squeeze and pull rocks in the same
    direction as the wave travels

14
S-Waves
  • S-Waves cause rocks to move at right angles to
    the direction of the wave

15
Surface Waves
  • Surface Waves move rocks up and down, as well as
    side-to-side
  • Motion is similar to an ocean wave

16
Focus
  • Earthquakes originate at a point called a Focus
  • Focus is usually below the surface
  • The Epicenter is the point on Earths surface
    directly above the focus

17
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