The primary

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The primary tool for investigating the physical
properties of the Earths interior is seismology.
Seismology
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• Seismology The study of seismic waves.
• Seismograph Instrument that records seismic
  waves.
• Seismogram The record of ground motion that is
  produced by a seismograph.

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The Earths Interior
Deep wells and boreholes (4 to 12 km)
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Density of Water 1 gm/cm3
Crust 2.6-3.1 gm/cm3
Mantle 3.3-5.7 gm/cm3
Outer Core 10-12 gm/cm3
Inner Core 13-14 gm/cm3
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Earthquake in Japan Magnitude 8.0 September 25,
2003 1950 UTC
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Izmit Turkey Seismogram
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• Two main groups of seismic waves.
• Body waves travel through the Earths interior.
• Surface waves are guided by the outer layers of
  the Earth.

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• Two types of body waves.
• P-waves
• Primary Waves
• first arrival
• S-waves
• Secondary Waves second arrival

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• P-waves and S- waves are distinguished from each
  other by the way they propagate through the
  Earth.

• P-waves push (compress) and pull (dilate) rocks
  in the direction the wave is traveling.

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S-waves shake the material at right angles to
their direction of travel.
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• P-waves can travel through solids, liquids, and
  gases because matter in all three of these states
  resists being compressed and will elastically
  spring back once the force is removed.
• S-waves can only travel through solids, because
  fluids do not resist shearing motion. So, fluids
  do not transmit S-waves.

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• Two main groups of seismic waves.
• Body waves travel through the Earths interior.
• Surface waves are guided by the outer layers of
  the Earth.

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• Two types of body waves.
• P-waves
• Primary Waves
• first arrival
• S-waves
• Secondary Waves second arrival

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• Two types of surface waves.
• Rayleigh waves Discovered by Lord Rayleigh
  (1887).
• Love waves Discovered by A.E.H. Love (1911).

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Data from station MBWA (Marble Bar, Western
Australia) last updated at Thu 10/30/03 1253
GMT
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In the case of surface waves, the ground motion
is concentrated near the surface of the Earth,
and the wave motion is similar to that of water
waves in the ocean.
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In the case of water waves, a particle of water
(or a toy boat) at the surface moves in a
circular pattern, but stays at the same
location. At greater depth, the water particles
also move in circles, but the circles are smaller.
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Rayleigh wave motion is similar to water wave
motion, except that for Rayleigh waves, the
circles are retrograde.
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Love waves have side-to-side ground motion,
similar to S-waves, except that the ground motion
decays with depth in a manner similar to Rayleigh
waves and water waves.
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Granite (and Average Continental Crust)
6.0 km/sec
2.5 km/sec
3.5 km/sec
3.0 km/sec
Differences in density and other physical
properties affect the velocity of seismic waves.
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Oceanic Crust P-wave Velocity 7 km/sec Basalt
Continental Crust P-wave Velocity 6
km/sec Granite
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Density of Water 1 gm/cm3
Crust 2.6-3.1 gm/cm3
Mantle 3.3-5.7 gm/cm3
Outer Core 10-12 gm/cm3
Inner Core 13-14 gm/cm3
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P-wave Velocities
Crust 6-7 km/sec
Mantle 8-13 km/sec
Outer Core 8-10 km/sec
Inner Core 10-11 km/sec
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