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#Post#: 163--------------------------------------------------
E HOT SPOTS
By: Admin Date: March 8, 2017, 1:58 pm
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New Concepts in Global Tectonics Newsletter, no. 38 3 ARTICLES
GULF OF CALIFORNIA ELECTRICAL HOT-SPOT HYPOTHESIS:
CLIMATE AND WILDFIRE TELECONNECTIONS
Bruce A. LEYBOURNE - leybourneb@hotmail.com
(Geostream Consulting LLC, www.geostreamconsulting.com)
Bay St. Louis, MS, USA
Giovanni P. GREGORI - giovanni.gregori@idac.rm.cnr.it
(Professor -Istituto di Acustica O. M. Corbino - Retired) Roma,
Italy.
Cornelis F. de HOOP - cdehoop@lsu.edu
(School of Renewable Natural Resources, Louisiana State
University Agricultural Center)
Baton Rouge, LA, USA
Introduction:
The prevailing view that radioactive decay is the major thermal
source for the interior of the planet may create limitations in
geophysical modeling efforts. New theoretical insights (Gregori
2002) provide for an electrical source from the
core-mantle-boundary (CMB) by a tide-driven (TD) geodynamo which
is enhanced by various solar induction processes. Joule heating
at density boundaries within the upper mantle and base of the
lithosphere from CMB electrical emanations may provide some of
the hotspot energy for upper mantle melts and associated
magmatism driving seafloor spreading and lithospheric rupture.
Estimates of the total budget of the endogenous energy of the
Earth supporting the electrical hot-spot hypothesis are as
follows (Gregori, 2002):
1) The general scenario is that the TD geodynamo has a very low
performance in terms of magnetic energy output (<<1%), while
almost its entire energy output supplies (via Joule’s heating)
the endogenous energy budget. Indeed it can be sufficient for
justifying the entire observed energy budget of the Earth, while
other sources, such as radioactivity, are just optional.
2) A different consideration is due to chemical and phase
transformation processes, occurring within deep Earth.
Observations are evident that the Earth operates like a car
battery, being recharged and discharged at different times. This
occurs by storing energy within the deep Earth interior. Within
a car battery, such storage occurs via a reversible chemical
reaction. In the case of the Earth, such storage occurs via a
conspicuous change of liquid vs. solid phase. It should be
stressed that such inference is a matter of observational
evidence, and of strict implications. It is NOT a result of any
kind of speculation.
3) The timing of such recharging and discharging is manifested,
as the most evident effect, in terms of the Earth’s
electrocardiogram, displaying one heartbeat every ∼27.4 Ma
(with an error bar of, say, < ±0.05 Ma). Every heartbeat elapses
a few Ma, and during it some large igneous province (LIP) is
generated. At present, we are close to the peak of one such
heartbeat, and a present LIP is Iceland.
4) The manifestation of such huge endogenous energy budget, at
least according to the observational evidence referring to the
last few million years, occurs in terms of a ∼ 60% release
as a gentle geothermal heat flow, while the entire remaining 40%
includes all other forms of energy, such as volcanism,
seismicity, continental drift or sea floor spreading,
geodynamics, and tidal phenomena. Therefore, the
planetary-integrated role of heat flow cannot be neglected (such
as it is being generally assumed when dealing with climate
models). Tectonic theorist might consider electrical stimulation
from the interior of the planet as a plausible driving mechanism
of surge channel activity and plate motions. This driver has
remained elusive in modern theoretical constructs.
Two recent lines of observational evidence linked to electrical
stimulation within a geologic hotspot exemplify the importance
of understanding this tectonic driving mechanism and testing the
validity of our hypothesis. The Guaymas Basin Rift, (Fig. 1, and
Fig. 2 – Area 2) a geologic hotspot within the Gulf of
California is considered a geothermal power source for the
region. In the first scenario gentle geothermal heat flow from
TD joule heating within the hotspot is invigorated during bursts
of regional seismic activity. Solar induced and electrically
stimulated seismic activity provides additional thermal energy
at the base of the lithosphere. This heat may take up to 6 - 7
months for transmigration and escape at the surface. This timing
is consistent with the observational data and rationally
explains the local sea surface thermal signatures over the
Guaymas Rift coincident with El Nino climate teleconnections
(Fig. 2 – Area 3 and 4). In the second scenario Coronal Mass
Ejections (CME) induce powerful surges of electrical activity
from the deep interior of the planet. These powerful surges
overcome resistance in the lithosphere by traveling along more
conductive zones generally associated with basaltic fault
intrusions and their signature geomagnetic anomaly trends.
Ionized gases may be forced through the fracture systems and
wildfires may be sparked by electrical arcing (lightning) or
direct combustion from intense joule heating near the surface.
The unprecedented wildfire storm in October 2003 occurred
simultaneously with a powerful CME. Geospatial wildfire patterns
suggests these wildfires followed fault and geomagnetic anomaly
trends associated with the extension of the East Pacific Rise
into the North American continent and Pacific fracture zones
traversing the west coast of California. Details of each
scenario are discussed below.
I. El Nino Climate Teleconnection
Sea Surface Temperature (SST) anomalies over the Gulf of
California/Baja (Fig. 2 - Area 2) are teleconnected to the peak
El Nino SST anomaly patterns also seen in Fig. 2. Note the
spurious SST anomaly over the Cocos Ridge associated with El
Nino (Fig. 2 – Area 3). Earthquakes beginning in November 1996
at the beginning of a solar sunspot cycle (Hale Cycle) signal
the beginning of an increased period of seismic activity
associated with heat inputs driving the 1997/98 El Nino (Fig.
3). Blot (1976) and Blot et al. (2003) indicate thermal
transmigration rates of approximately 0.15 km/day accounting for
the approximately 7 month delay of sea surface thermal
signatures after high impact earthquake bursts which even
triggered a small tsunami in Hawaii (Walker, per. com). Seismic
precursors to El Nino by 6-7 months have also been documented
(Walker, 1988, 1995 and 1999) over the last 7 recent El Nino
events. The resulting clustered seismic activity is hypothesized
to be electrical in nature and is associated with joule heating
at density boundaries near the base of the lithosphere (Gregori,
2000 and 2002). Electrical stimulus of these earthquakes is
highly suspect, especially below the lithosphere. This scenario
provides a geophysical mechanism for explaining the SST anomaly
teleconnections. These SST anomaly patterns overlying earthquake
events are hypothesized to be the result of increased heat
emission from seafloor volcanic extrusions and/or associated
hydrothermal venting. The volcanism is triggered by electrical
bursts from the core-mantle-boundary induced by solar coupling
to the internal geodynamo. The larger implication is that El
Nino may be solar-tectonically modulated (Leybourne, 1997;
Leybourne and Adams, 2001).
Cedros Trench Cedros Trench Guaymas Basin Rift Salton Trough
Fig. 1. SST drape over bathymetry in the Gulf of California
Salton Trough region exhibits thermal anomalies coincident with
the adjacent Cedros Trench. Thermal signatures in this area are
often teleconnected to El Nino SST anomalies off the coast of
South America. The Guaymas Basin Rift is the likely energy
source for this local thermal signature and is a known geologic
hot-spot supplying Southern California with geothermal power
(Image by Haas 2002, NAVOCEANO-MSRC). New Concepts in Global
Tectonics Newsletter, no. 38 5
1- US. West Coast2 – San Andreas/Guaymas3 – Central America4-
South America
Fig. 2. Eastern Pacific SST anomalies peak in January of 1998
during 97/98 El Nino event in area 2 - San Andreas/Guaymas. This
corresponds to the viewing angle in Fig. 1 exhibiting
teleconnection SST anomalies over Guaymas Rift and Cedros
Trench. Area 3 Central American exhibits the main intertropical
convergence SST anomaly coincident with spurious teleconnection
pattern over the Cocos Ridge trend (NAVOCEANO-MSRC).
Fig. 3. (a) Two distinct clusters of earthquakes off the Coast
of South America in Nov. 96 are apparent. (b) SST’s seem to
emanate in a similar pattern to the earthquake paired clusters.
The northern SST anomaly is on the continental shelf as is the
northern earthquake cluster, while the southern SST anomaly is
further offshore over the continental slope as is the southern
earthquake cluster. These SST anomalies appeared (June 1997)
just north of earthquake positions possibly due to prevailing
long shore currents, about 7 months after the paired earthquake
clusters. (c) Chart indicates earthquakes/day (frequency),
magnitudes are added for simple power indicator (magnitude add),
along with an average (magnitude avg). A spike in earthquake
activity begins Nov. 12th and tapers off Nov. 14th revealing the
intense episodic nature of these events. (d) SST Max.
Anomaly/month indicating anomalies > 7° C by June 97 followed by
a year of elevated SST anomalies associated with the 97/98 El
Nino. (e) Joule energy released during (f). Earthquake events
Nov. 96.
II. Wildfire Teleconnection
Wildfire outbreaks during a period of geomagnetic storms in
October 2003 may be linked to electrical emanations from within
the earth (Leybourne et. al., 2004). In late October 2003, a
powerful Coronal Mass Ejection (CME) directed straight at Earth
erupted on the Sun’s surface, when wildfires simultaneously
broke out along an arc shaped pattern of geomagnetic anomaly
trends extending from Mexico to north of Los Angeles (Fig. 4).
The wildfire ignitions slowed dramatically when the CME period
ended. The geomagnetic anomalies are inter-splayed by fault
systems connected to the Gulf of California hotspot through the
San Andreas Fault complex and to the Hawaii hotspot through the
Murray Fracture Zone. These orthogonal fault systems intersect
in the San Gabriel Mountains where a huge wildfire out break
occurred near strong geomagnetic signatures (Fig. 5). Strong
electrical impulses emitted from the CMB during CME may not only
joule heat local geologic hotspots, but unconverted superfluous
electrical energy and ionic plasmas could be transmitted further
along conductive igneous complexes (generally associated with
geomagnetic signatures) and fault systems through the
lithospheric fractions of the earth, arcing to power lines and
igniting tree lighter or underbrush. In 1859 during the
strongest CME on record, telegraph wires in western United
States and Europe caught fire and were destroyed. Potential
voltage differences between hotspot locations may create
electrical ground shorts at geomagnetic intersection areas (Fig.
6), starting fires near power line circuits or from discharges
directly to the ionosphere. An electrical hot-spot hypothesis
based on Gregori’s theoretical construct is understood in terms
of deep earth electromagnetic induction coupled to solar
perturbations. The induction process creates anomalous electric
currents from the internal-geodynamo.
Fig. 4. Arc-shaped fire pattern appears linked to geomagnetic
anomaly trends (insert).
HTML http://activefiremaps.fs.fed.us/fire_imagery.php?firePick=southern_california;<br
/>
HTML http://pubs.usgs.gov/sm/mag_map/
mag_s.pdfNew Concepts in Global
Tectonics Newsletter, no. 38 7
Fig. 5. Geomagnetic anomalies in San Gabriel Mountains along
intersecting faults and mylonite units.
HTML http://wrgis.wr.usgs.gov/docs/gump/anderson/rialto/rialto.html
Fig. 6. Geophysical composite map: a) Basalt flow remnant
magnetization signatures indicating global hotspot locations and
indicated Pacific links (Quinn, 1997). b) Southern California
geomagnetic crustal anomalies have coincident links to the San
Andreas orthogonal fault complex associated with an intersection
in the San Gabriel Mountains where a huge wildfire outbreak
occurred near the strong geomagnetic signatures during the
October, 2003 CME (USGS 2002). c) Pacific Ocean Basin GEOSAT
structural trends indicating possible electrical conduits (red
lines) between Murray (North) and Molokai (South) Fracture Zones
which intersects at Hawaiian, Guaymas, and Juan de Fuca hotspots
(orange circles), geographical links (green lines) (Smoot and
Leybourne, 2001). d) Southern view in Fig. 1 with geographical
links (Haas, 2002).
Conclusions:
Thus, Earth’s endogenous energy may stimulate ocean basin
heating associated with El Nino from episodes of increased
seismic stimulation and electrical wildfire propagation during
CME via geologic hotspot controls. Atmospheric pressure
teleconnections are also suspected (Namias, 1989) in some cases.
A distinction is made between the control on the TD geodynamo
exerted by the e.m. induction within very deep Earth (i.e.
within the mantle, which occurs only for e.m. signals of some
very low frequency, say with a period T > 22 years), and the
e.m. solar induction within some much shallower structures
characterized by much higher frequencies and much shorter
periods. Such kinds of phenomena also include the e.m. induction
effects within manmade systems, such as power lines (causing
blackouts), pipelines, and communication cables (Meloni et al.,
1983; Lanzerotti and Gregori, 1986). Should we address these as
distinct phenomena? The relationships between the different e.m.
signals within such different frequency bands is not clearly
defined but these various affects at different time scales may
to some degree be physically driven by electrical stimulation
from the interior of the planet.
References:
Blot, C., 1976. Volcanisme et sismicite dans les arcs
insulaires. Prevision de ces phenomenes. Geophysique 13, ORSTOM,
Paris, 206p.
Blot, C., Choi, D.R. and Grover, J.C., 2003. Energy
transmigration from deep to shallow earthquakes: A phenomenon
applied to Japan –Toward scientific earthquake prediction-. New
Concepts in Global Tectonic Newsletter, Eds. J.M. Dickens and
D.R. Choi, no. 29, p. 3-16.
Gregori, G., 2002. Galaxy-Sun-Earth Relations: The origins of
the magnetic field and of the endogenous energy of the Earth.
Arbeitskreis Geschichte Geophysik, ISSN: 1615-2824, Science
Edition, Schroder, W., Germany.
Gregori, G., 2000. Galaxy-Sun-Earth Relations: The dynamo of the
Earth, and the origin of the magnetic field of stars, planets,
satellites, and other planetary objects. In Wilson A., (ed.),
2000. The first solar and space weather conference. The solar
cycle and terrestrial climate. ESA SP-463, 680p., European Space
Agency, ESTEC, Noordwijck, The Netherlands, p. 329-332.
Gregori, G., 1993. Geo-electromagnetism and geodynamics: “corona
discharge” from volcanic and geothermal areas. Phys. Earth
Planet. Interiors, v. 77, p. 39-63.
Haas, A., 2002. Figs. 1, 2, and 3d. Produced by: Major Shared
Resource Center (MSRC) at Naval Oceanographic Office
(NAVOCEANO), Stennis Space Center, MS, 2002.
Leybourne, B.A., 1996. A tectonic forcing function for climate
modelling. Proceedings of 1996 Western Pacific Geophysics
Meeting, Brisbane, Australia. EOS Trans. AGU, Paper # A42A-10.
77 (22): W8.
Leybourne, B.A., 1997. Earth-Ocean-Atmosphere coupled model
based on gravitational teleconnection. Proc. Ann. Meet. NOAA
Climate Monitoring Diag. Lab. Boulder, CO., p. 23, March 5-6,
1997. Also: Proc. Joint Assemb. IAMAS-IAPSO. Melbourne,
Australia, JPM9-1, July 1-9.
Leybourne, B.A. and Adams, M.B., 2001. El Nino tectonic
modulation in the Pacific Basin. Marine Technology Society
Oceans ’01 Conference Proceedings, Honolulu, Hawaii.
Leybourne, B.A., Haas, A., Orr, B, Smoot, N.S., Bhat, I., Lewis,
D., Gregori, G., and Reed, T., 2004. Electrical wildfire
propagation along geomagnetic anomalies. The 8th World
Multi-Conference on Systemics, Cybernetics and Informatics,
Orlando, FL., p. 298-299 (July 18-24).
Meloni, A., Lanzerotti, L.J., and Gregori, G., 1983. Induction
of currents in long submarine cables by natural phenomena. Rev.
Geophys. Space Phys., v. 21, no. 4, p. 795-803.
Namias, J., 1989. Summer earthquakes in southern California
related to pressure patterns at sea level and aloft. Scripps
Institution of Oceanography, University of California, San
Diego. Journal of Geophysical Research, v. 94, # B12, p.
17,671-17,679.
Quinn, J.M., 1997. Use of satellite geomagnetic data to remotely
sense the lithosphere, to detect shock-remnant-magnetization
(SRM) due to meteorite impacts and to detect magnetic induction
related to hotspot upwelling. International Association of
Geomagnetism and Aeronomy, Upsala, Sweden.
Smoot, N.C. and Leybourne, B.A., 2001. The Central Pacific
Megatrend. International Geology Review, v. 43, no. 4, p. 341,
2001.
USGS –United States Geological Survey, 2002. Magnetic anomaly
map of North America. Dept. of the Interior.
HTML http://pubs.usgs.gov/sm/mag_map/
mag_s.pdf;
HTML http://wrgis.wr.usgs.gov/docs/gump/anderson/rialto/rialto.
html
Walker, D.A., 1988. Seismicity of the East Pacific: correlations
with the Southern Oscillation Index? EOS Trans. AGU. v. 69, p.
857.
Walker, D.A., 1995. More evidence indicates link between El
Ninos and seismicity. EOS Trans. AGU, v. 76, no. 33.
Walker, D.A., 1999. Seismic predictors of El Nino revisted. EOS
Trans. AGU, v. 80, no. 25.
#Post#: 167--------------------------------------------------
PREVENT ERUPTIONS
By: Admin Date: March 13, 2017, 7:29 pm
---------------------------------------------------------
3/16/17, 11:34AM
Charles Chandler - Hi Charles. On Tuesday I told Dong Choi,
editor of NCGT, that the Electrical Hot Spots article he
published around 2004, which described Earth as an electrical
battery, is similar to your model and that, if your model is
right, you have an idea how to stop eruptions and possibly
quakes. He replied that he agrees that Earth acts like a leaky
battery and explains many things well, including John Casey's
finding that earthquakes correlate with sunspot minima. He said
he looks forward to receiving your manuscript. I mentioned your
model, because I thought he might be interested in your idea for
stopping eruptions. But he said he doesn't think nature's acts
are stoppable, although he said it's an interesting idea and who
knows, maybe it would work.
I noticed that Jeff Wolinsky had a brief mention of his model
and links to his videos in NCGT's 3rd quarter issue last year.
So it looks like NCGT will be hopefully a good place to
publicize much of your model. I think they may even like to
publish your tornado model, because they seem to be very
interested in learning to prevent natural disasters, at least
via prediction and preparation. G'Day
-----
Tuesday, March 14, 2017 3:33 AM
From: "Dong Choi (NCGT)" <editor@ncgt.org>
I look forward to receiving Charles Chandler's manuscript. I
agree that the Earth acts like a battery. This explains many
phenomena very well. The earthquake - solar cycle
anticorrelation is also well explained by the leaky battery
theory, as proposed by Giovanni Gregori. Electric Earth is the
way to see the real Earth.
I don't think nature's acts - volcanic eruptions and earthquakes
- are stoppable. But the idea is very interesting. Something to
keep thinking for us. One day, it may become a reality. Who
knows?
I am watching Indonesian volcanoes. They will be a sentinel of
the coming mini-ice age. Don't forget California and New Madrid.
We will detect when a huge energy is released from the Earth's
outer core. There must be some signs.
---
Hi Dr. Dong Choi. Tuesday, 14 March 2017 11:24 AM
Thank you for the book suggestion. I'm waiting to see if it's
available via the library first.
I just read Dark Winter and got a lot of good info from that.
I'll try to get the new book soon.
Last week I read from NCGT Newsletter no. 38 the article, GULF
OF CALIFORNIA ELECTRICAL HOT-SPOT HYPOTHESIS, which is
interesting and is similar to my friend Charles Chandler's
model. Both agree that the Earth acts like a battery that
generates electric currents. Charles developed his model about 4
years ago. I told Charles about the article and suggested that
he inquire about possibly submitting some of his material to
NCGT. Charles' model is much more thorough than the NCGT
article, but the latter was written around 2004, so they may
have developed their model more by now.
If Charles' model is close to correct, he has determined how
volcanic eruptions and earthquakes could possibly be stopped.
Quakes would be more difficult, because a final quake would be
triggered, so people would have to be evacuated. But for
volcanoes he says a 5 km deep borehole some distance from the
volcano should stop eruptions, like lightning rods prevent
lightning damage. The borehole would act like a lightning rod
for electric currents from the Moho, causing the nearby volcano
channel to freeze up gradually. He says a borehole near an
earthquake fault could heal the fault, which is an idea that I
think your co-editor Louis Hissinck is familiar with. But a
nuclear explosive would need to be dropped into the borehole in
order to produce a shock wave that would seal it. He thinks a
good test site would be Istanbul where a fault is near the
surface, requiring little drilling. As for the volcano nearby
boreholes, he estimated they'd cost about $20 million to drill 5
km deep.
So, in light of John's and your findings about quakes and
eruptions being triggered by solar minima in conjunction with
planetary tidal influences, it seems that humanity might be able
to prepare for catastrophic events by preventing them, at least
in part. I suppose the Indonesian volcanoes would be the most
important ones to prevent from erupting.
Do you have any comments?
--------------------------------------------
On Thu, 3/9/17, Dong Choi (NCGT) <editor@ncgt.org> wrote:
Subject: RE: Surge Tectonics
Date: Thursday, March 9, 2017, 4:20 AM
Hi, Lloyd, The book you need to read is; "Surge tectonics: a new
hypothesis of global geodynamics", authored by Arthur Meyerhoff
and others. Kluwer Academic Publishers in 1996. The book has
been cited numerous times in our papers. I am one of the
co-authors of this book. Art Meyerhoff was the greatest
geologist our history ever had. I am glad I am one of his
students; he raised me to occupy the present position - editor
of NCGT Journal. The book presents scientific grounds of the
surge tectonics. The book appeared two years after his death.
The surge channel is identified by the presence of low velocity
lenses or layers under inactive or active tectonic belts in the
upper mantle. In the New Madrid paper I showed the presence of a
low velocity lens under the Mississippi Valley. The low velocity
lens is where liquid or gas is contained and energy or magma
flow occurs. Although I did not specifically refer to the surge
channels in many of my papers, their presence is confirmed in
many seismic tomographic images.
As you may have noticed already, the current geology is facing
serious challenges; same as politics - fake news, fake science.
Political correctness and financial correctness distort factual
evidence. Plate tectonics have been dominating the geological
scene for over 50 years, but no evidence has ever been
presented. All hard data show otherwise - vertical tectonics is
the primary movement. We have documented numerous evidence that
shows the sunken continents in the present oceans.
I am glad there is a serious person who reads our papers
objectively. Please ask me anything, I'll try to answer as much
as I can. Dong Choi
-----Original Message-----
From: lloyd kinder Sent: Thursday, 9 March 2017 4:06 PM
To: Dong Choi (NCGT) <editor@ncgt.org>
Subject: Surge Tectonics
Hi Mr. Choi. From what I've read so far in NCGT, it seems that
there have been considerable successes using Surge Tectonics to
predict major earthquakes. Do you recall if there are any
writings in NCGT that specify what exact evidence there is for
surge channels and migration of surge energy from the mantle to
the surface? I enjoy many of the illustrations, tables and maps
in NCGT, but haven't yet come across the kinds of evidence for
surge channels that I hope to read soon. I hope you may be able
to refer me to one or more NCGT journal or newsletter issues
that have such evidences. Otherwise, can you refer me to any
books or papers outside of NCGT, esp. something fairly recent?
Thanks for any help or just a reply.
#Post#: 168--------------------------------------------------
Re: E HOT SPOTS
By: Admin Date: March 15, 2017, 10:51 am
---------------------------------------------------------
522 New Concepts in Global Tectonics Journal, V. 4, No. 3,
September 2016. www.ncgt.org
Caveats on tomographic images
Gillian R. Foulger (g.r.foulger@durham.ac.uk), Giuliano F.
Panza, Irina M. Artemieva, Ian D. Baslow, Fabio Cammarano, John
R. Evans, Warren B. Hamilton, Bruce R. Julian, Mechele Lustrino,
hand Thybo and Tatiana B. Yanovskaya.
Terra Nova, v. 25, no. 4, p. 259–281, 2013. doi:
10.1111/ter.12041.
(The following is an exerpt from Summary of this paper.
Permission granted by the senior author)
Summary
Problems with travel-time tomography include inadequate
correction for structure outside the study volume, inability to
retrieve three-dimensional structure, corruption of the mantle
image by inadequate correction of the crust and boundary layer
beneath, inability to retrieve true anomaly amplitudes and
inhomogeneous ray coverage. Some regions simply cannot be imaged
using current techniques, particularly in remote oceanic
regions. Perhaps the most vexed problem is assessing
realistically the true errors in results. Because of the
fundamental experimental set-up, errors in structures calculated
using teleseismic tomography are largest in the vertical
direction. This results in a propensity to downward-smear
structures, producing artificially vertically elongated
anomalies. For surface-wave tomography, lateral resolution of
anomalies is poorest and therefore lateral smearing can be
strong.
The information in three-dimensional models is difficult to
impart in a few maps and cross-sections. The wide array of
choices, such as which particular result to favour, and which
colour palette, line of section, and zero-contour wave speed to
select, means that there is broad scope for producing figures
that support preferred models. The widespread use of relative
wave speeds commonly leads to misinterpretations. Translation of
seismic anomalies to geology is not straightforward. More
physical parameters vary in the mantle than seismic parameters
mapped. Simplifying assumptions, such as seismic wave speed
being everywhere a direct proxy for temperature, are not
supported, and neither are geochemical models that rely on such
work.
The wave speeds of both compressional and shear-waves are
anisotropic in the mantle, and if this is neglected, which is
usually thecase, erroneous results and interpretations may
result. The upper 200 km of the mantle is the most heterogeneous
and anisotropic region of the mantle and beneath this,
heterogeneity drops dramatically (Gung et al., 2003). Many weak
anomalies imaged by seismic tomography may result simply from
uncorrected anisotropy. Anisotropy at ~200 km beneath cratons
and at ~80 - 200 km beneath ocean basins may be related to shear
in the boundary layer, the difference in depth simply reflecting
a variable depth to the maximum shear (Anderson, 2011).
In recent years, much progress has been made in improving
computational techniques and incorporating these advances into
tomographic practice. This includes using local structure in
global parameterizations, and three-dimensional ray-tracing
instead of assuming straight or piecewise- straight rays (Hung
et al., 2001, 2004). Similarly, Christoffersson and Husebye
(2011) have revisited the basics of the inversion methods used,
showing that at least some of the often-noted smearing and
weakening of velocity anomalies by traditional damped inverses
can be mitigated by using better tuned methods. Progress is also
being made on describing better the uncertainties in the
results, including calculating probability density functions
(Mosegaard and Tarantola, 2002; Sambridge, 1999a,b). However,
these advances cannot eliminate the fundamental difficulties we
have highlighted above, which are inherent in the experimental
setup. There is, nevertheless, a good case for re-processing
many older data sets that have only been analysed using earlier,
more primitive methods, the results of which continue to
influence dynamic models of the mantle.
Other seismic results that do not depend on tomography should be
included in interpretations, and interpretive work should
emphasize only the deductions that are required by the data.
Published, coloured tomography images and simplistic, cartoon-
like interpretations should be treated with scepticism. Blue
colours in tomographic cross-sections cannot be assumed to
indicate cold, sinking material and red cannot be assumed to
indicate hot, rising material. Likewise, increased awareness is
needed that petrology/geochemistry cannot, in general, determine
the depth of origin of magma sources. As a consequence, joint
interpretation is more difficult than commonly realized. A more
cautious approach will enable the current, unprecedented
experimental tools available in both seismology and
petrology/geochemistry to contribute reliably to answering the
fundamental questions about the structure and dynamics of the
Earth’s interior that have been disputed ever since plate
tectonics was accepted and still remain controversial.
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