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3.11: Earth’s Major Boundaries Revealed By Seismic Waves

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    9828
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    Earth’s Major Boundaries Revealed By Seismic Waves

    The Moho (Mohorovicic discontinuity): (Discovered in 1909 by Andriaja Mohorovicic)
    • The Moho is the boundary between the crust and the mantle. It separates less dense crustal rock from underlying denser mantle rock.
    • Identified by a change in the velocity of P waves

    The core-mantle boundary (CMB): (Discovered in 1914 by Beno Gutenberg)
    • Based on the P-wave shadow zone
    • No P waves from 105 to 140 degrees
    • The fact that S waves do not travel through the outer core provides evidence for the existence of a non-solid layer beneath the mantle
    • Showed existence of liquid outer core and overlying mantle

    Lehmann Discontinuity (Predicted by Inge Lehmann in 1936)
    • Boundary between outer and inner core defined by an increase in seismic wave velocity from outer to inner core and by seismic wave reflection off the solid inner core.

    The locations of the Moho, CMB, and Lehmann Discontinuity are shown in Figures 3-8 and 3-17.