Is Hawaii a deep
plume…
Or a wide slow deep
fracture zone?
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Don L. Anderson
December 2009
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>3 second delays;
much greater than
Hawaii
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Science, Dec. 2009
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TOMOGRAPHY IS
THE STUDY OF
SHADOWS
As Plato showed, shadows can
be deceiving
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Plato’s Cave
…things are not always what they seem. In Plato's
cave people see only shadows and these are the
only reality there is…they kill the messenger from
the outside…
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Steeply arriving teleseismic rays give a fuzzy view
and can easily be misinterpreted (parallax,
smoothing, smearing, streaking, bleeding, rabbitearing, shallow structures…)
SKS waves have the additional complication of Ultra
Low Velocity Zones at the CMB &
other complications in the complex
D” region…
The controversy between Zhang-Tanimoto and
Dziewonski et al. about the depth of midocean ridges
was traced by Masters to the effect of D”
heterogeneity…which was misinterpreted as being
due to deep slow ridges…
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A cylinder and a pillbox both give a tent or cone
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A suture or fracture zone (FZ) can be 50 km wide,
200 km deep and have S-wave deficits of 8 %
(fluids, mineralization, cracks) to 35 % (high pore
pressure, open dikes, wet rifts…). This will affect
teleseismic arrivals, but in a different way than a
shallow pillbox or a vertical cylinder or than most
resolution tests.
A finite fault zone can give rabbit ear artifacts…or
fuzzy drips off the edge of the structure.
If 8 % anomalies are ruled out (Wolfe) then the
shallow fault zone will be smeared into the deep
mantle…
A wide FZ under the Hawaiian chain?
farside
S
source
SKS
SKS delays are right above the FZ; FZ area
and delay are correctly determined
S delays are smaller, shifted; far side; average
delay (station term) is very much smaller, and
effect is over a larger area.
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If there are only a few
stations to the SE of the
Hawaiian FZ anomaly, the
FZ slowness will be
projected to great depth
and will not be cancelled
out by crossing rays.
Elementary optics…
ar
e
Qu
i ckTi m
e™
an
d
a
de
co mp r
e sso r
n
eed
ed
to
see
th
is
p i ctu
re.
If there are only a few
stations to the SE of the
Hawaiian FZ anomaly, the
FZ slowness will be
projected to great depth
and will not be cancelled
out by crossing rays.
Elementary optics…
This is not a plume…it is
Sherlock…
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“Science”
Dec.2009
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SKS 1000-1500
There are few
rays or crossing
rays at depth of
proposed plume
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S & SKS
A possible artifact of
station and source
sparcity to the SE
Cracks through thick lid (70 km) to fertile blob from
120 km to 200 km
NORMAL
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SKS
Wolfe,
Solomon
ULVZ (E.Pacific)
Laske, Phipps
Morgan & Orcutt
D
E
P
T
H
~1000-km arrays; ~3-sec delays
Similar data sets led to quite
different conclusions
Deep plume
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Hawaii
2
sec
Shallow rift
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Jimez
Lineament
A simple approach to the joint inversion
of seismic body and surface
waves applied to the southwest U.S.
Michael West, New Mexico State, Gao &S.Grand
source
RISTRA
3 sec total variation
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farside
HAWAII
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A simple approach to the joint inversion
of seismic body and surface
waves applied to the southwest U.S.
Michael West, New Mexico State, Gao &S.Grand
360 km
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West et al.
Rabbit ear artifact
Body wave
only inversion
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West et al.
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Rabbit ears artifacts
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Yellowstone
Rabbit ear artifacts?
Hawaii
Wolfe et al. 2009
Iceland
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Hawaii
00
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SKS ray
These are among the latest arrivals to the Hawaiian
array from any earthquake (which is to the west); slow
trend is along chain; there are also more slow stations
(>4) for this event than for others
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Typical S-delays in western N.America are much
larger & are due to upper mantle
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Upper Mantle Convection Beneath the Central Rio Grande Rift Imaged by
P and S Wave Tomography
1
1
2
3
4
Wei Gao , Stephen P. Grand , W. Scott Baldridge , David Wilson , Michael West , James
4
3
F. Ni and Richard Aster
1
Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712
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University of Texas
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• These good men of
HartO’Stan
• To dogma much inclined,
• Much feared to see an
Elephant
• (Though all of them were
blind),
•
Since any observation
•
Might stultify the mind
It’s a PLUME!
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•
•
•
•
•
•
•
The Noble Men, one fore two aft
Inhaled the pachyderms exhalations
"Tis from the deep bowels" offered one
"A signature of intestinal fermentations".
"Tis primordial gas", gasped another
We'll get a Nobel prize for our exertations
Or at least a Science paper, with no deliberation!
I did resolution
tests!
THE TAIL OF THE PLUME
•
•
•
•
•
•
It was six souls in research strong
To learning much inclined,
Who went to study mantle plumes
Which they no doubt would find.
Lacking an Alternative,
Nothing else could be divin'd.
•
•
•
•
•
•
These good souls of Academe
To dogma much inclined,
Much feared to see an Elephant
(Though all of them were blind),
Since any observation
Might stultify the mind
•
With bulbous Head, and skinny
Tail
A pachyderm paced by, undetect’d.
Emitting fluids and various gases,
Enormous lips and trails of ejecta
This might be the plume
Which they all had expect'd.
•
•
•
•
•
•
The First, a physicist, approached,
Leaving Guyot Hall in fear
Fell against his sturdy side,
And spoke so we could hear
“God bless me! but the Elephant
Is exactly like a sphere!"
•
•
•
•
•
•
•
•
•
•
•
The Second, feeling around below,
Cried, “Ho! we have here a mushroom
Very round and smooth and straight!
No further need to fume.
This wonder of an Elephant
Is certainly a plume!”
•
The Third, demurred, he had his own
theory,
•
But he tripped and fell (there was little •
room),
•
A squirming trunk brushed his face,
•
He spake with a sense of doom:
•
“I fear,” quoth he, “the Elephant
•
Really is a plume!”
•
•
•
•
•
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•
•
•
•
•
•
The Fourth, who chanced to touch its
brow,
Said: “Not an animal at all. I, instead
Can tell what this resembles most;
Deny not the fact" she said
"This marvel of an Elephant
Is just a plume head!”
The Fifth no sooner had begun
About the beast to groom,
Than, seizing on the swinging tail
That tangled with his broom,
“I agree,” quoth he, “the Elephant
Is very like a plume!”
…let’s look [only] at…features where
a plume…makes…geological sense and
investigate
those.
Hofmann
& Hart,
Science
2007
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ex cathedra
…let’s look [only] at…features
where a plume…makes…geological
sense and investigate
those. H & H,
Science 2007
“Seek and ye shall
find…”
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