Seeing inside the Earth Glossary

  1. Core-mantle boundary
    An interface 2,900km below the Earth's surface separating the mantle and core.
  2. Inner core
    The inner section of the core 5,155km deep to the Earth's centre at 6,371km, and consisting of solid iron alloy.
  3. Low-velocity zone
    The asthenosphere underlying oceanic lithosphere in which seismic waves travel more slowly, probably because rock has partially melted.
  4. Lower mantle
    The deepest section of the mantle, stretching from 670km down to the core-mantle boundary.
  5. Moho
    The seismic-velocity discontinuity that defines the boundary between the Earth's crust and mantle.
  6. Outer core
    The section of the core, between 2,900km and 5,150km deep, that consists of liquid iron alloy.
  7. P-wave shadow zone
    A band between 103 and 143 degrees from an earthquake epicentre, as measured along the circumference of the Earth, inside which P-waves do not arrive at seismograph stations.
  8. Reflection
    The bouncing off of a ray as it hits a boundary between two different materials.
  9. Refraction
    The bending of a ray as it passes through a boundary between two different materials.
  10. S-wave shadow zone
    A band between 103 and 180 degrees from the epicentre of an earthquake inside of which S-waves do not arrive at seismograph stations.
  11. Seismic ray
    The changing position of an imaginary point on a wave front as the front moves through rock.
  12. Seismic-reflection profile
    A cross-sectional view of the crust made by measuring the reflection of artificial seismic waves off boundaries between different layers of rock in the crust.
  13. Seismic tomography
    Analysis by sophisticated computers of global seismic data in order to create a three-dimensional image of variations in seismic-wave velocities within the Earth.
  14. Seismic-velocity discontinuity
    A boundary in the Earth at which seismic velocity changes abruptly.
  15. Transition zone
    The middle portion of the mantle, from 400 to 670km deep, in which there are several jumps in seismic velocity.
  16. Upper mantle
    The uppermost section of the mantle, reaching down to a depth of 400km.
  17. Velocity-versus-depth curve
    A graph that shows the variation in the velocity of seismic waves with increasing depth in the Earth.
  18. Wave front
    The boundary between the region through which a wave has passed and the region through which it has not yet passed.
Card Set
Seeing inside the Earth Glossary
Adapted from 'Earth: Portrait of a planet'. Marshak, 2005, W. W. Norton & Company, Inc.