Updated 12/23/09

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What about Hawaii?

• 1/24/09
• Updated 12/23/09

Don L. Anderson
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Normal vs Plume Convection

• Normal mantle convection is driven by internal
  radioactive heating, secular cooling by heat
  conducted to the surface through a thermal
  boundary layer
• The scale of this convection is measured in
  thousands of km involves ?Ts of 100s of degrees
• Superposed on this is an independent
  hypothetical smaller scale (lt200-km) and hotter
  (gt200 C) form of convection

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If the inside of the Earth were filled up with
uniform slow (red) fast (blue) cubes, then the
globes distributions of earthquakes seismic
stations would return the image on the right
Note the poor resolution in the Pacific. Actual
data returned the image on the left (From Li et
al.). Note the similarity between the real Earth
and the fake Earth around Hawaii south of New
Zealand the redness of poorly sampled regions
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Note that only red regions are recovered in the
Pacific
much of the Indian ocean
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GLOBAL TOMOGRAPHIC MAP
COMPARE RED REGIONS WITH THOSE RECOVERED FROM THE
FAKE MANTLE
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600 km depth
Ritsema et al.
SEMANTICS
There are many large low velocity regions in the
mantle. These have the scales of normal mantle
convection, not mantle plumes
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Ridges hotspots require extension. Slabs
displace warmer material out of TZ.
TECTONICS
Global extension (red)
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The test model has a uniform pattern of high and
low velocity blocks. Near vertical rays (P,PKP,
S, SKS) convert this pattern to vertical slow
cylinder
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Near vertical rays
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