Earth Structure

• the internal layers of the earth in descending order:

  crust

  upper mantle

  asthenosphere

  lower mantle

  outer core

  inner core
• what type of rock is the earths crust composed of?

  silicic and mafic rock
• ultra mafic peridotite makes up which layers of the earth?

  upper mantle, asthenosphere, lower mantle
• what metals are the inner and outer core made of?

  iron and nickel
• what is the unique property of the asthenosphere?

  it is 5% molten
• what layers of the earth comprise the lithosphere?

  crust and upper mantle
• how do geologists know what the earth's internal structure looks like?

  seismic waves
• what are the two types of body waves produced by an earthquake?

  primary and secondary waves
• what other type of waves do earthquakes produce apart from P and S waves?

  surface waves
• what device can measure seismic waves?


  seismometer
• do P or S waves have a higher velocity?

  P waves
• P waves are:

  low amplitude and fast moving compression waves that reach a seismometer first
• S waves are:


  slower moving shear waves that reach the seismometer second
• focus


  the point within the earth's crust where an earthquakes occurs/originates
• epicentre


  the point on the earth's surface immediately above the earthquake focus
• what type of waves are primary waves?

  -compressional

  -longitudinal
• what property determines the velocity of P waves?


  incompressibility
• what is the velocity of P waves in the crust?

  6.0km s-1
• what materials can P waves move through?

  solids

  liquids

  gases

  (not through a vacuum)
• what type of waves are S waves?

  -shear

  -transverse
• what property determines the velocity of S waves?

  rigidity
• what velocity can S waves move in the crust?

  3.5km s-1
• why can't S waves travel through the the outer core?

  S waves are shear waves and they cannot shear liquid
• from an earthquake's focus, how many degrees around the earth can S waves travel?

  103 degrees
• what is the S wave shadow zone?

  area between 103 degrees both ways from an earthquake's focus, where the S waves from that earthquake cannot reach
• what happens to P waves when they travel through the inner cores?

  they refract and travel slower through the outer core (liquid) and then increase velocity again through the inner core
• what is the P wave shadow zone?

  the area around the globe between 103 degrees and 142 degrees, from an earthquake's focus, where P waves cannot reach
• how is it theorised that the earth's core was formed?

  iron meteorites
• what type of meteorite is theorised to make up the mantle?

  stony meteorites