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Studying Earth's Interior

Objectives:

    1.    Describe how data from earthquakes are used to infer the structure of Earth's interior.

Key Terms:

    Shadow zone    Moho    Transition zone

Notes: (10-4)

Seismologists, by studying the seismic waves in Earth, have been able to give us a reasonable picture of the Earth's inner core.  To accomplish this seismologists have incorporated some basic properties of waves.

Waves travel slower in a more dense medium
P-waves travel faster than S-waves
S-waves travel only through solids.

seismic.gif (317199 bytes)

(ircamera.as.arizona.edu/NatSci102/ movies/seismic1.gif)

Evidence for the structure of the Earth:

1.    Absence of S-waves on the opposite side of the Earth from the focus of a major earthquake

Supports the liquid outer core of Earth

2.    The refraction (bending) of the P-waves at the outer core border and the absence of S-waves creates an area containing no seismic waves known as a shadow zone.

3.    Seismic waves increase in speed as they cross the boundary between the upper and lower mantle known as the Moho discontinuity.  (named after the Croatian scientist Mohorovicic)

4.    Transition zones mark the abrupt changes in the velocities of the seismic waves as they pass through the different layers of Earth.

 

 

Last modified: November 10, 2003