Download Seismic Profiles of Earth`s Interior

Seismic Profiles of Earth’s Interior
Objective: Use seismic waves to determine the nature of
Earth’s interior layers
Scientists learn about Earth’s interior by using seismic waves or vibrations
that travel through Earth’s layers during earthquakes. There are different
types of seismic waves. P waves (Primary waves) are compressional
vibrations that travel accordion style through solids and liquids. S waves
(Secondary waves) are transverse. They travel in a snake-like fashion, but
only through solid mediums. Surface waves travel in a variety of methods,
but only along the solid crust.
Seismic waves change speed and angle as they move through different
mediums. In general, seismic waves travel faster through solids or rigid
densely packed materials.
1
Radius = 6370 km
Mantle
Crust
Liquid iron
outer core
Solid iron
inner core
http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html
http://www.uh.edu/~jbutler/physical/chapter19.html
Distance to core is ~1/2 the radius (2900 km depth)
Core
Mantle
Crust
Sulfur (4%)
Nickel
(11%)
Iron (85%)
Density:
~11 g/cm3
Density:
~5 g/cm3
Density:
~3 g/cm3
Types of Seismic Waves
4-6 km/s
2-3 km/s
P (primary) and S (secondary) waves travel through Earth’s interior
info about the mantle and core (density, composition)
Surfaces waves (Love, Rayleigh) travel through the crust
 info about the crust
Seismic Wave Velocity
Density
(composition)
Physical State
Which rock will seismic waves travel
the fastest through: Sandstone or
Periodotite? Give a reason why.
Seismic waves travel faster through:
solids or liquids?
Reflection and Refraction
Refraction
Reflection
This is what happens to
seismic waves in the Earth.
Waves BEND or REFRACT
when they move through
different mediums.
Seismic Wave Reflection
• Used to find depth to boundaries (density discontiniuites)
P-Wave Reflections: P waves can travel through solids or liquids
P-Wave Shadow Zone
Indicates depth to the
core-mantle boundary
S-Wave Shadow Zone
Indicates that the outer
core is liquid
Seismic Velocity Profile of Earth
Speed in km per second
liquid
C
B
A
D
Depth below surface (km)
solid Seismic
Key Idea:
Waves Travel
FASTER in
DENSER Material
Seismic Velocity Profile of Earth Activity
Key Idea: Seismic Waves travel FASTER in denser material.
1. Which seismic waves travel faster: S (secondary) waves or P (Primary) waves? (P or S wave)
2. How does the speed of seismic waves change from A  B (0 – 670 km depth)?
(Speed up/ Slow down / Stay constant, the same)
3. Give a reason for the change in speed from A  B (the first 670 km depth). Hint: what can
influence the speed of seismic waves?
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4. Compare the speed of seismic waves in the upper and lower mantle. Seismic waves travel (faster/
slower / at the same speed) in the lower mantle.
5. Give a reason for the change in speed between the upper and lower mantle. Hint: what can
influence the speed of seismic waves?
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Seismic Velocity Profile of Earth Activity
Key Idea: Seismic Waves travel FASTER in denser material.
solid
liquid
gas
Use the picture of the Structure of Solids and Liquids from above to answer the following question.
5. Which are denser: (Solids or Liuids)? Denser means more tightly packed).
6. Which would you expect seismic waves to travel faster through: (Solids or Liquids).
7. What happens to waves between C and D? Why?
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The Crust & Mantle: Close Up
8. Summarize how seismic waves allow .us to “see” inside Earth.
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Convection in the Mantle
subducted slabs
large-scale
convection
CMB
mantle
plumes