Download Studying the Earth s Interior Layers using Earthquakes What can

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Layers of the earth
Chapter 19 Understanding Earth
Studying the Earth s Interior Layers using Earthquakes
• Review of the layers of the Earth
• Using Earthquakes
• Reflection and Refraction
• Distinguishing liquid from solid inside the Earth
• Variations in velocity inside the Earth
• Earthquake shadow zones
• Tomography
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Reflection and
refraction of light
What can happen to seismic waves traveling through the
Earth s interior?
When light, sound, or
other waves, including
seismic waves,
encounter a boundary
between two materials
the waves may be
reflected and/or bent
(refracted).
• May travel through different materials/layers at different speeds
- faster velocities through more rigid/denser materials
- S-wave velocities drop to zero in liquids (blocked, can t pass
through)
Fig. 19.1 Understanding Earth
• May be bent (refracted)
- abruptly at boundaries
- gradually throughout a layer with variable properties
• May be reflected at boundaries
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Lithosphere (includes crust)
}
Crust
Mantle
Outer Core
(liquid)
transition
transition
transition
transition
P-wave and S-wave velocities in
the earth s interior.
Fig. 19.5 Understanding Earth
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Inner Core
transition
Seismic velocities at
the base of the crust
and in the upper
mantle.
Note the large
changes in velocity at
the Moho and the
base of the
lithosphere. Also note
the relatively low
velocities of the
Asthenosphere (lowvelocity zone).
Fig. 11-5 Chernicoff Geology 2nd
Edition
Asthenosphere
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Thickness of the Earth s crust measured in km – Mooney et. al., 1998
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P-wave and S-wave shadow zones
There are areas which the waves from an
earthquake do not reach. P-wave shadow
zones are caused by the refraction of Pwaves at the core-mantle boundary
(boundary between solid mantle and liquid
outer core).
Most ocean crust
is less than 10 km
thick (average 6-8
km)
Continental crust
ranges from about
10 km to 80 km,
but most is
between 30 and
45 km thick.
S-wave shadow zones occur because Swaves cannot pass through liquids. The
shadow zones tell us how deep the coremantle boundary is and that the outer core
is liquid.
Fig. 19.2 Understanding Earth
Next: shadow zone animations
Seismic Tomography – Using earthquakes to probe the interior much like x-
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rays are used in a CT scan of the human body.
Example:
Seismic scan of Earth links deep mantle plumes
with volcanic hotspots
http://www.sciencedaily.com/releases/2015/09/150902134939.htm
http://phys.org/news/2015-09-ct-scan-earth-links-deep.html
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