Seismology

• what are the two types of body waves?

  P waves and S waves
• what are the characteristics of body waves?

  faster and less damaging
• which type of body wave is primary?

  P waves
• which type of body waves are secondary?

  S waves
• what are the two sets of waves which P waves arrive as?

  direct waves and diving waves
• where do P waves form?


  zones of compression and dilation
• which type of body wave is faster?

  P waves
• where do P and S waves travel?

  through the earth
• what are the two types of seismic waves created by earthquakes?

  compressional waves and shear waves
• how do shear waves move?

  side to side motion
• how do compressional waves move?

  push pull motion
• are solids more resistant to compression or shearing?

  compression
• do compressional or shearing waves move faster through solids?

  compressional
• what is another term for compressional waves?

  P waves
• what is another term for shearing waves?

  S waves
• where is the P wave shadow zone?

  between 105 and 142 degrees
• where is the S wave shadow zone?

  the area below 105 degrees
• what is the shear modulus in liquids and gases?

  zero
• what is the upper continental crust made of?

  low density granite rock
• what is the deep sea floor made of?

  basalt and gabbro overlain by sediments
• where does the velocity of P waves increase abruptly?

  the Mohorovcic discontinuity
• what is the mantle below the Moho made primarily of?

  dense peridotite
• where is earth's crust the thinnest?

  under the oceans
• where is earth's crust the thickest?

  under mountains in orogenic zones
• what term refers to the difference is seismic wave velocities between two layers of material?

  seismic discontinuity
• how deep is the moho in oceanic regions?

  5 - 10 km
• how deep is the moho in continental regions?

  20 - 80 km
• what is the crust comprised of?

  gabbro
• what is the mantle comprised of?

  peridotite
• what happens to S waves passing through the asthenosphere?

  they are slowed down and more energy is absorbed
• why can S waves pass through the asthenosphere?

  it is only partially molten
• what does the lithosphere asthenosphere boundary depend on?

  local temperature gradient rather than chemical composition
• what is the rock above and below the lithosphere asthenosphere boundary?

  peridotite
• what is the main mantle mineral?

  olivine
• why is there a mantle transition zone?

  change in crystal structure (not composition or state) of main mineral olivine
• what happens to olivine at the mantle transition zone?

  it changes to a higher pressure form = denser structure - same atoms, more closely packed
• what happens to olivine at 670 - 700 km (the moho)?

  structural change from 4 fold to 6 fold co ordination = even more densely packed
• what does the moho separate?

  the crust from the mantle
• what happens to the mantle at the lithosphere asthenosphere boundary?

  it becomes partly molten