Walter Brown discussion with Glenn Morton on subduction
James J. Lippard
---------- Forwarded message ----------
Date: Sat, 16 Aug 1997 18:37:18 -0500
From: Brad Anderson <webm...@creationscience.com>
To: crea...@creationscience.com
Cc: grmo...@ns.waymark.net, wa...@creationscience.com
Subject: [Creation Forum] Re: Proof of Subduction (long)
Dear Glenn,
I want to reply to your several letters addressing mine of 9 August,
highlight some issues still on the table, and summarize apparent areas of
agreement and disagreement.
You initially had specific disagreements with my analysis showing why a
plate cannot subduct. You said: (1) I used too small a value for the
compressive strength of rock, (2) rocks flow, and (3) something akin to
ball bearings or powder reduce friction on subducting plates. I presume
you have retracted those objections. You now say that my math is good, no
set of numbers that you care to propose will allow plates to subduct, but
something must be wrong with my analysis because earthquakes happen. We
are making progress.
I explained that while both earthquakes and hypothetical subducting plates
involve moving deep rock, it is poor logic to say that one phenomenon
implies the other. The mechanisms and forces for each are different. As
one example, I cited the likely mechanism for deep earthquakes to show that
those earthquakes do not imply that plates subduct. You then agreed, but
now say that shallow earthquakes imply that plates can subduct, overthrusts
can occur, and mountains can buckle. Again, I say faulty logic; the
mechanisms and forces are different. Let's call this Issue #1.
One evening in 1986, Bob Dietz invited me to join five or six geologists
for supper at a local restaurant. (He was nice not to introduce me as a
creationist. That would have disturbed some people.) Sitting next to me
was an expert on mountains. In telling me about his research, he
volunteered that "We don't understand how mountains form." All I could say
is, "I know." He was describing, in a convoluted way, the problem I
explained in the technical note "Can Overthrusts Occur? Can Mountains
Buckle?". Although the textbooks do not discuss it, Glenn, the problem is
real--and to "the initiated," serious.
Related to this is another acknowledged problem about overthrusts. The
experts on the mechanics of overthrusts have almost unanimously arrived at
a near solution to this old paradox--but one they can't imagine ever
happening. The fault surface must be lubricated by water. They frequently
refer to the "water pore pressure" under the slab increasing to the point
where gravity sliding will occur. Trouble is, how do they accumulate
enough high pressure water under a horizontal slab without the water
flowing away? Furthermore, elevations must change to gain potential energy
to drive the thrusting. Of course, all they can visualize are slow
processes--over millions of years. We all know that high pressure water
will not stay collected under a horizontal plate for millions of years, or
several days for that matter. So these experts are stuck, and they don't
talk about it much, except rarely in scientific journals that are almost
always read by believers in millions of years. You might want to read a
classic paper by M. King Hubbert and William W. Rubey, "Role of Fluid
Pressure in Mechanics of Overthrust Faulting," _Bulletin of the Geological
Society of America_, Vol. 70, February 1959, pp. 115-166. If you like, I
will give you thirty other references.
If you study the hydroplate theory you will see that one common element in
the proposed mechanisms for overthrusting and mountain building is vast
quantities of water acting as a lubricant. A second is enormous kinetic
energy. A third is momentum. (In other words, a concentrated force is not
required.) None of these elements are present in your hypothetical
subducting plates. If water lubricated the interfaces between a subducting
plate and the mantle, rock pressure would drive water upwards. However,
deep, trapped water that was in the subterranean chamber will migrate into
sealed earthquake faults. Since the water is pressurized from below
lithostatically, not hydrostatically, gigantic forces slowly reduce
frictional locking along earthquake faults.
I hope you can see why mechanisms and forces, things most geologists have
little interest in, are crucial to understanding how things work and how
certain things got here. The simpleminded belief that time is the answer
is pitifully lazy. Those who don't look for and test mechanisms
instinctively, will likely grab at the easy, but wrong, answer--some poorly
defined process acting for millions of years. A Ph.D. geologist, who
visited me for two days recently, put it this way: "Most classic geologists
are unfortunately trained to describe things, not understand and analyze
mechanisms."
At that same supper I mentioned above, I asked everyone there to tell what
they thought was the biggest problem in geology. I forget most answers,
but when my turn came, I said that we need to understand what drives
lithospheric plates. A full professor (sedimentologist) disagreed. When
I asked why he didn't think it was much of a problem, he said, "Because we
know plates are moving." Again, no desire to understand mechanisms,
forces, and energy sources.
Once I gave Dietz a list of reasons why I did not believe natural
convection occurred in the mantle. I was surprised to learn that he had
already reached that conclusion, but for one or two reasons that had never
occurred to me. When I urged him to publish something on that, he smiled
but declined--as if to say doing so would be professional suicide. When I
related this story to a friend, Dr. Douglas Block (a geology professor for
40 years), he got on a plane and flew from Chicago to Phoenix, so I could
introduce him to Dietz. Doug, who was in the midst of a sabbatical
studying "Problems with Plate Tectonics" wanted to hear for himself this
startling admission from one of the world's leading geologists and one of
the founders of the plate tectonic theory. Doug heard it, just as I had
described.
Mechanisms are critical, and I will press you, Glenn, to explain them.
Simply saying that "it's irrelevant," or "if rock moves in one situation,
it must move in a completely different situation," won't cut it.
I asked you how subduction begins. You have not addressed this Issue #2.
If you do, you will face another big difference in mechanisms and realize
that subduction cannot even begin.
Issue #3: Your explanations for earthquakes vs. mine. Why are you acting
as if I don't believe earthquakes below 4.9 miles and plate movement occur?
(I and others on the Creation Forum do not need you to send us useless
pages listing scads of earthquakes.) I have suggested explanations for
earthquakes or plate movements in the Hydroplate Overview chapter. If you
had read it, you would realize that I know earthquakes (and sudden movement
along faults) occur. The earthquake mechanisms (one for deep earthquakes,
in endnote 34, and one for shallow earthquakes) appear to answer the
questions and problems described in three earlier paragraphs in that
chapter. Again, let me ask you, Glenn, how do you explain those questions
and problems?
At the risk of oversimplifying, I will try to summarize what I believe
causes most shallow earthquakes. But don't take this as a reason for not
studying the entire chapter.
I gave many evidences showing that during the flood continents drifted,
crushed, and thickened rapidly; mountains were pushed up; and the 16 km
deep Atlantic floor rose to its present average depth of 4 km. All of this
caused plastic deformations within the mantle that continue even today.
These shifts built up stresses throughout the mantle and plastic regions of
the lithosphere. Mass shifts also caused deep phase changes, producing
slow expansions at ridges and contractions at trenches.
(I believe even more dramatic shifts of mass occurred, which I may publish
some day. If I am correct, subduction zones or Benioff zones are actually
paths of weakness resulting from mantle movements soon after the
compression event. Trenches, downbuckled regions, resulted from mantle
movements that were primarily directed through the earth toward the rising
Atlantic floor. Another powerful driving force throughout the mantle was
gravity, tending to keep the deformable earth "spherical.")
Faults, formed primarily as a result of the compression event, are
sometimes weakened (or lubricated) by deep migrating water driven into the
fault plane by lithostatic pressure. With sufficient weakening within
faults and increasing differential stress across faults, slippage begins.
This generates frictional heating along the fault, converting the liquid
water to steam almost instantaneously, unlocking the fault even more, and
causing a runaway shallow earthquake.
Issue #4. I cited a recent tomographic study that, if you accept their
assumptions and beliefs and do not study their data carefully, might make
you believe in subduction. [See R. D. Van der Hilst et al., "Evidence for
Deep Mantle Circulation from Global Tomography," _Nature_, Vol. 386, 10
April 1997, pp. 578-584.] I pointed out that their "subduction" is not
where anyone would have ever predicted, and no sign of subduction exists in
the expected places. Below (marked by ">") are my responses to ALL your
statements concerning this Issue #4.
>The subduction zones are where they should be.
Please cite any PREVIOUS prediction of subduction under the east coast of
North America and from eastern Europe to Indonesia. Why "in the world" are
so many signs of subduction missing near all the trench regions in and
surrounding the Pacific? While you may think things are "where they should
be," Richard Monastersky writing about this study in _Science News_, Vol.
12, 19 July 1997, p. 47, said, "Strangely, neither of the new reports shows
deep slabs where geophysicists most expected them: in the northwest
Pacific."
>They are offset from the present day subduction location because
>the subducting slabs don't go down at a 90 degree angle.
Who ever claimed that slabs subduct at 90 degrees?
>Some subducting slabs descend at 10 deg
>initially then increase the rate of descent.
You do not know that plates are subducting, or that they descend at 10
degrees. The theory you accept makes those claims.
Such shallow angles almost double the forces preventing movement that I
laid out in the technical note you dispute (Issue #1). Stick in the
numbers, and see for yourself. Shallow angles also make initiating
subduction more difficult. I will elaborate once you explain how
subduction begins (Issue #2).
>Figure 3 is of a level 1350 km deep. Thus, at this level,in the America's
>you must look for the subduction quite a distance east of California. A 20
>degree rate of dip gives a distance of 3700 km to the east. However,
>since the rate of dip increases, the location of the subducting zone is
>about 1000 km to the east of California. See the diagram.
>
>surface subduction point
> |<---3700 km->
>--------------------------------
> \ 20 deg. |
> \ |1350 km deep
> \ |
> \ |
> \ |
> \ |
No. Figures 1b and 1c show details at depths of 600 km and 900 km,
respectively. One can see no plate subducting diagonally from western
North America down to eastern North America.
If a subduction zone is about 1000 km east of California, where is the
trench and the Benioff zone? Can you give a citation where a subduction
zone was claimed east of California?
>A comparison of the model (Figure 2) and the observations Figure 3
Figure 2 is not a model. Figure 2 is "synthetic data calculated from
assumed input models." If cold slabs were 1300 km deep at the locations
shown in Figures 2a and 2c, they and noise would alter seismic waves in
certain ways. Inverting that "synthetic data" in a computer, gives the
very sharp results shown in Figures 2b and 2d. Now compare the SHARP,
NARROW images they got with artificial data to the FUZZY, WIDE images using
real data (Figures 1b-1f and 3). This implies that what is really there is
not a plate. Besides, who in their wildest dreams would have predicted
plates there in the first place?
>You have misinterpreted those two figures. For anyone who wants to go see
>these pictures, realize that colder material has a faster velocity. Since a
>subduction plate is still colder than the surrounding material it should
>have a faster velocity.
Relatively fast seismic velocities at certain points in the mantle MAY mean
the rock there is relatively cold. Mineralogy variations or phase changes
could also be an explanation. In other words, colder rock will speed up
seismic waves, but fast seismic waves do not mean the rock was colder.
Your calling it a colder region is one possible interpretation, not a
measurement. For a complex set of reasons which I will skip for now, I
suspect fast = cold, but let's not overlook that hidden assumption you and
many others make.
>The figures you cite are entirely consistent with subduction.
For reasons I gave above (FUZZY, WIDE, and WRONG LOCATIONS), I disagree.
>Figure 3 shows the velocity of sound at 1350 km deep
>(which is deeper than the melt point of the subducting
>plate, yet it is still cooler than the surrounding medium.
Look at Figures 1b-1f, which give pictures at many depths. There is no
trace of any subduction. Notice Figure 1d is Figure 3 from a different
perspective.
>Figure 3 shows a linear faster velocity region
>from Europe to southern Asia which is consistent
>with the subduction along the Tethys margin.
Even believers in the mythical "Tethys Sea and Tethys margin," don't claim
they extend beyond the Mediterranean area. Your comment about the eastern
Europe to Indonesia anomaly being "consistent with subduction along the
Tethys margin," is a POSTdiction, not a PREdiction. Can you cite a
prediction that a plate should be there? It is always easy, once you make
a surprising measurement, to restructure a flexible theory to fit the data.
>The West coast show a .5% faster velocity
>under California, down through Peru.
Only at a depth of 1300 km. Figures 1b-1f show no fast rock diagonally
above or below it. Apparently, no subducting plate is there.
>The only anomaly is the faster Velocity along the East coast of the
>US which may be due to deep, cool roots of the Appalachian mountains.
Only anomaly? I have listed many. Deep? The Appalachians would not have
roots anywhere near 1350 km. Besides, the Appalachians do not form a chain
above the fast (maybe cold) rock. The fast rock goes from the Hudson Bay
down through Florida, through the Gulf of Mexico, and finally to the
northern boundary of Peru. The Appalachians do not.
>Figure 4 is worthless for your case and supports mine.It is 1800-2000 km
>deep. The faster velocity material once again is across the Himalayan
>subducting zone, then turns north up Eastern Asia Alaska, and is almost
>connected down the America's. The reason the faster material in the
>America's is off to the east of the present coastal subduction is to the to
>angle of the descending flow.
I have already shown, by referring to Figures 1b-1f, that the data does not
support your "descending flow."
>Figure 4 is actually better support for subduction
>than Figure 3 yet both support subduction.
You don't understand what Figure 4 shows. Read its caption carefully. At
first glance it seems to support plate tectonics, because they put in
ARTIFICIAL DATA BASED ON PLATE TECTONICS. In other words, the data is
intentionally phony. Figure 4's purpose is to show the excellent
resolution of the data processing procedure. Notice the patchwork of tiny,
fast regions--which they call "slablets--in the real data. According to
plate tectonics, there should not be these hundreds of disconnected fast
regions. Since the data processing procedure gives high resolution, I
suspect this study measured real, tiny, fast patches in the mantle--but
those patches don't fit plate tectonics or a mantle that has been
convecting (mixing) for billions of years. Notice how often the paper
talks about "heterogeneities"--meaning lots of patches. Look in Figures
1b-1f and Figure 3 at all the small fast regions under Asia--completely
inconsistent with subduction. If plate tectonics were correct, we should
see subducted plates that are BIG, SHARP, THIN, and AT THE RIGHT PLACES.
We don't see any of these four characteristics.
>You also fail to mention figure 5 which clearly shows the faster material,
>expected from a cold subducting slab beign .5% faster (blue) descending into
>the mantle. How can you possibly say that these authors failed to observe
>subduction? Figure 5 IS SUBDUCTION!!!!
Figure 5a can only be interpreted loosely as a subducting plate. I agree
that on one vertical plane they found a diagonal fast region. But notice
how thick and irregular the diagonal region is. Figures 5b and 5c, using
"synthetic" or artificial data, show what a subducting plate should look
like. Figure 5a, presumably the best example the authors could find in the
world, doesn't look like a subducting plate should. Although the fast
region points up toward a trench in the pictures we are shown, it falls
short of connecting with the trench by at least 500 kilometers.
Furthermore, the missing connection is a slow region, not a fast or even a
normal region--just the opposite of what it should be if your
interpretation were correct. A subducting slab would be a three
dimensional feature. Wouldn't you think if they truly found a subduction
plate, their pictures would display its interesting three-dimensional
shape? Not hard to do. (See p. 91 of _In the Beginning_, 6th general
edition.)
I spoke earlier of the large shifts of mass within the mantle, especially
under what are now trenches. I believe tomographic studies are seeing the
effects of these shifts.
>I would strongly urge any interested party to go look
>at the Figure 5 of the article Walter cites above.
I agree. But study it and all the figures carefully. Then compare Glenn's
interpretation with mine.
Issue #5: The Alaskan Earthquake. You referenced an article on the Alaskan
earthquake [George Plafker, "Tectonic Deformation Associated with the 1964
Alaska Earthquake," _Plate Tectonics and Geomagnetic Reversals_ edited by
Allan Cox (San Francisco: W. H. Freeman and Company, 1973), pp. 311-331.]
Some of your statements must be answered.
>Subduction is really nothing more than
>a continent overthrusting the ocean floor.
No, it's not. Subduction, if it could happen, would be the slow diving of
a lithospheric plate hundreds of kilometers into the mantle. Friction
would act on both the bottom and TOP of the plate. The plates are
typically 30-50 miles thick, hundreds or thousands of kilometers wide, and
thousands of kilometers long. The leading face of the plate would
experience incredible drag, since rock has to be pushed out of the
way--somewhere. Also, buoyant forces would tend to lift the plate.
Remember isostasy?
In contrast, overthrusting requires a relatively short, narrow, and thin
slab to break from or somehow separate from its foundation. Once rapid
movement begins, friction acts on only the bottom of a nearly horizontally
moving plate. Relatively little drag acts on the front of the slab.
Displacements are orders of magnitude less than that visualized in
subduction.
>The asterisks [in Glenn Morton's sketch] mark the
>subducting oceanic plate boundaries and the overlying
>region is the continent overthrusting the oceanic plate.
There is no basis for concluding that a subducting plate was involved in
the Alaskan earthquake, even if you have drawn a picture. Had there been
subduction, the continental region would have risen (and shortened). In
fact, it subsided (and lengthened by 2.7 meters). Plafker, the article's
author, said as much on page 330. "The most serious limitation of the
thrust-fault hypothesis lies in its attempts to account for the observed
subsidence to the north of the zone of uplift." If you insist on a
subducting plate being involved, then you should conclude that it slid up
and out from under Alaska, allowing the continental region to sink. More
seriously, because so much land rose to the southeast and sunk in the
northwest, a major conclusion should be that mass shifted from the
northwest to the southeast. That is just the opposite of what plate
tectonics would predict.
Notice Plafker's use of the words "thrust fault" and "hypothesis." A
thrust fault is not a subducting plate. In fact, Plafker never used the
words: subducting plate, subduction, subducting, or plate. He did
entertain the possibility of "progressive underthrusting of the oceanic
crust and mantle beneath the continental margin" but admitted that it was
"largely speculative." Besides, the thrust-fault hypothesis for the
Alaskan earthquake is only one of several educated guesses on the fault's
location. My guess is that mass shifted to the southeast in the low
velocity zone of the upper mantle, where shear stress is a minimum--perhaps
zero. Consistent with this is Figure 1b, in Van der Hilst et al., which
shows that part of Alaska has very slow seismic velocities at 600 km depths.
>F, the focus of the earthquake, occurred
>about 50 km deep near the Benioff zone . . .
The focus was 20-50 km deep. No clearly defined Benioff zone is shown.
You are treating locations of aftershocks from the 1964 earthquake as if
they were epicenters of many earthquakes. Some aftershock origins were
only 5 km down. A Benioff zone connects epicenters of many earthquakes.
If a plate subducted along the path you are implying, its slope with the
horizontal would be between 3.1 and 7.6 degrees. I have already explained
the problem with shallow subduction angles.
So far, I have responded to objections and topics YOU INITIATED concerning
subduction, overthrusts, and mountain building. Once we reach as much
agreement as possible on Issues #1 - #5, I will have some interesting
questions for you on other aspects of these topics. To keep our exchange
"bite-sized," let me suggest we address these five issues one at a time.
You may choose the order.
Walt
Libertarius
GENESIS DOES NOT ASSUME AN OMNIPOTENT/OMNIPRESENT "GOD"
It is clear from the Genesis story that its writers never thought
that the "God" in their story was either omnipresent or omniscient,
nor did they believe in immortality.
According to the story, "God" told A&E that they would die the
SAME DAY, if they ate from the forbidden fruit. Obviously, if
they had been created immortal, this could not have happened,
anyway. BUT, the story tells us that the snake knew it better than
"God", so, indeed, they did NOT die but lived on to have lots
of children. So, "God" was NOT "omniscient". Also, "God" did not
know where A&E were hiding in the garden, when he was walking
through the garden and looked for A&E.
Also, "God" was obviously not present when A&E ate the fruit,
nor when they decided to hide.
As for immortality, the story tells us that "God" chased A&E
out of the garden so that they could not eat from the Tree of
Life and become immortal.
Libertarius
==================================
DON'T CONFUSE FICTION WITH REALITY
==================================
James J. Lippard
Yes, it was.
In article <$i99$1...@shell6.ba.best.com>, Mark Isaak <at...@best.comNOSPAM> wrote:
>In article <Pine.BSI.3.96.970816...@usr07.primenet.com>,
>[much deleted]
>>
>>We all know that high pressure water will
>>not stay collected under a horizontal plate for millions of years, or
>>several days for that matter.
>>
>>Walt
>
>Is that really Walt Brown who said that? If so, he has just demolished
>his own theory, since his theory depends on huge amounts of high
>pressure water staying pooled under the crust for several decades at
>least.
>--
>Mark Isaak at...@best.com http://www.best.com/~atta
> "To undeceive men is to offend them." - Queen Christina of Sweden
>
--
Jim Lippard lippard@(primenet.com ediacara.org skeptic.com)
Phoenix, Arizona http://www.primenet.com/~lippard/
PGP Fingerprint: B130 7BE1 18C1 AA4C 4D51 388F 6E6D 2C7A 36D3 CB4F
James J. Lippard
Glenn's response:
From grmo...@ns.waymark.net Sun Aug 17 13:57:18 1997
Date: Sun, 17 Aug 1997 13:13:52 -0500
From: Glenn Morton <grmo...@ns.waymark.net>
To: Crea...@creationscience.com
Subject: [Creation Forum] Re: Proof of Subduction (long)
Dear Walt,
I hope you are well.
At 06:37 PM 8/16/97 -0500, Walt wrote:
>You initially had specific disagreements with my analysis showing why a
>plate cannot subduct. You said: (1) I used too small a value for the
>compressive strength of rock, (2) rocks flow, and (3) something akin to
>ball bearings or powder reduce friction on subducting plates. I presume
>you have retracted those objections.
Why would you assume this? No where did I write a retraction. When I
retract, you will know it because I will write it. (see below for an example)
>You now say that my math is good, no
>set of numbers that you care to propose will allow plates to subduct, but
>something must be wrong with my analysis because earthquakes happen. We
>are making progress.
I didn't say your math was good. I said it was irrelevant. The meaning of
irrelevant, according to my dictionary does not mean "good".
>One evening in 1986, Bob Dietz invited me to join five or six geologists
>for supper at a local restaurant. (He was nice not to introduce me as a
>creationist. That would have disturbed some people.) Sitting next to me
>was an expert on mountains. In telling me about his research, he
>volunteered that "We don't understand how mountains form." All I could say
>is, "I know." He was describing, in a convoluted way, the problem I
>explained in the technical note "Can Overthrusts Occur? Can Mountains
>Buckle?". Although the textbooks do not discuss it, Glenn, the problem is
>real--and to "the initiated," serious.
Not when the Alaskan earthquake can move surface rocks 200 km or more from
the epicenter which is 50 km deep. As a manager of Geophysics for my company,
I deal with lots and lots of geological experts in structural geology (indeed
I use seismic data to infer structure). The experts I deal with have no
problem such as you describe.
>
>If you study the hydroplate theory you will see that one common element in
>the proposed mechanisms for overthrusting and mountain building is vast
>quantities of water acting as a lubricant.
As I noted before, water is NOT a lubricant for faults. it actually increases
friction. let me quote this again. You obviously didn't see it.
"Concerning the lubricating effect of water, Terzaghi (1950, p. 91) has shown
that water definitely is not a lubricant on rock materials, and its presence,
if anything tends to increase the coefficient of friction"~M.K. Hubert and
W.W. Rubey, "Role of Fluid Pressure in Mechanics of Overthrust Faulting,"
Bulletin Geol. Soc. Amer., 70, February, 1959, p. 129.
>I hope you can see why mechanisms and forces, things most geologists have
>little interest in, are crucial to understanding how things work and how
>certain things got here.
Well I am a geophysicist, not per se a geologist. Profesionally, my group uses
seismic data to infer the structure of the earth. Thus, you cannot dismiss me
as having "little interest" in these things. I am interested in forces and I
know that the strength of material's increases with increased confining
pressure. Your model ignores that fact.
>
>I asked you how subduction begins. You have not addressed this Issue #2.
>If you do, you will face another big difference in mechanisms and realize
>that subduction cannot even begin.
Here is how it begins.
The first thing one needs to know is a simple geometric fact we all learn in
high school. The shortest distance between any two points is a straight line.
An arc, connecting two points is longer than the straight line. Remember that
the earth's surface is a curved surface. In the diagrams below, the original
surface is marked by the -. The uplifted surface or the depressed surface is
a +. In the case of an upwelling, the curved surface of the earth is extended
or ripped apart. The length of material connecting A and B on the original
surface is insufficient to connect A and B on the Uplifted surface. The arc
length is greater.
gap gap gap
++++++ ++++++++ +++++++++++++++ +++++
+++ ----- +++
+++++ ---------------- ---------------- +++++
------------ ------------
---- ^ ----
-- | --
A upwelling B
The gaps form because there is not enough material to bridge the longer
distance.
Now for downwelling
-------
---------------- ----------------
------------ ------------
----- -----
-- --
A+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++B
downwelling
|
V
Since in the downwelling portion, as the mantle material flows down, there is
no support for the arch and it sags. This means that an arc length of 1000
km, must now fit into 995 km. This means that there is compression and the
brittle crust will break and form an overthrust.
-------
---------------- ----------------
------------ ------------
----- -----
-- ++/ --
A++++++++++++++++++++++++++++++++ / +++++++++++++++++++++++++++++++++++++B
/++
downwelling
|
V
The symbol / marks the plane of the thrust fault.
The stress will break the rock and cause an overthrust which initiates the
subduction process.
>
>(I believe even more dramatic shifts of mass occurred, which I may publish
>some day. If I am correct, subduction zones or Benioff zones are actually
>paths of weakness resulting from mantle movements soon after the
>compression event. Trenches, downbuckled regions, resulted from mantle
>movements that were primarily directed through the earth toward the rising
>Atlantic floor. Another powerful driving force throughout the mantle was
>gravity, tending to keep the deformable earth "spherical.")
>
Since the Benioff zones are thousands of kilometers long, you are saying that
movement can occur over that distance, yet your math says it can't.
>Issue #4. I cited a recent tomographic study that, if you accept their
>assumptions and beliefs and do not study their data carefully, might make
>you believe in subduction. [See R. D. Van der Hilst et al., "Evidence for
>Deep Mantle Circulation from Global Tomography," _Nature_, Vol. 386, 10
>April 1997, pp. 578-584.] I pointed out that their "subduction" is not
>where anyone would have ever predicted, and no sign of subduction exists in
>the expected places. Below (marked by ">") are my responses to ALL your
>statements concerning this Issue #4.
Yes it is and I explained why. Why does not the shallow angle at which the
plate subducts, and the depth of their maps not suffice as an explanation?
simple trigonometry calculates that at 1350 km deep, the subduction would no
longer be under the trench.
>
>>The subduction zones are where they should be.
>
>Please cite any PREVIOUS prediction of subduction under the east coast of
>North America and from eastern Europe to Indonesia. Why "in the world" are
>so many signs of subduction missing near all the trench regions in and
>surrounding the Pacific? While you may think things are "where they should
>be," Richard Monastersky writing about this study in _Science News_, Vol.
>12, 19 July 1997, p. 47, said, "Strangely, neither of the new reports shows
>deep slabs where geophysicists most expected them: in the northwest
>Pacific."
Walter, the front cover of that Science News shows four depths and the
subduction. The shallowest is 700 km deep, then 1000 km, 1300 km and 1600 km.
At 700 km the subducting plate is in the center of North America. As one goes
deeper, the cold subducting plate moves eastward. In the diagram below, S
marks the subduction location for that depth
North America
W.Coast E. Coast
surface S
700 km S
1000 km S
1300 km S
1600 km S
The subducting slab gets deeper as one goes eastward. The subduction is not
at the east coast. Except as an extension to the subduction which occurred
formerly at the west coast.
A look at the figure on p. 46 of July 19, 1997 Science News, shows a region of
higher velocity dipping to the east. This is consistent with subduction.
>You do not know that plates are subducting, or that they descend at 10
>degrees. The theory you accept makes those claims.
No, the angle of earthquakes (the Benioff zone) and the mapping of faster
material makes me say that. It is observation, not theory.
>
>Such shallow angles almost double the forces preventing movement that I
>laid out in the technical note you dispute (Issue #1). Stick in the
>numbers, and see for yourself. Shallow angles also make initiating
>subduction more difficult. I will elaborate once you explain how
>subduction begins (Issue #2).
Why would you withhold knowledge until someone explains something else? By the
way, I did explain it above.
>
>>Figure 3 is of a level 1350 km deep. Thus, at this level,in the America's
>>you must look for the subduction quite a distance east of California. A 20
>>degree rate of dip gives a distance of 3700 km to the east. However,
>>since the rate of dip increases, the location of the subducting zone is
>>about 1000 km to the east of California. See the diagram.
>>
>>surface subduction point
>> |<---3700 km->
>>--------------------------------
>> \ 20 deg. |
>> \ |1350 km deep
>> \ |
>> \ |
>> \ |
>> \ |
>
>No. Figures 1b and 1c show details at depths of 600 km and 900 km,
>respectively. One can see no plate subducting diagonally from western
>North America down to eastern North America.
See the front cover of Science News, July 19, 1997, which you so cheerfully
cited earlier.
>
>If a subduction zone is about 1000 km east of California, where is the
>trench and the Benioff zone? Can you give a citation where a subduction
>zone was claimed east of California?
Sure. What has happened is that the continent has overriden the subducting
zone in the Western US, cutting off the subducting plate. here are two
references.
"The North American Cordilleras are more complex than the Andes, from which
they differ in several respects. Along the broad coastal zone, notably in
California and in Oregon, numerous subduction complexes are exposed. Best
known is the Franciscan complex, a gigantic melange with blocks of ocean floor
rocks and trench sediments chaotically tumbled together. East of the
Franciscan, the the Great Valley, ophiolitic rocks covered by Mesozoic
turbidites are believed to represent oceanic crust underlying an outer trench-
arc gap."~Robert M. Shackleton, "The History of the Earth's Crust," in David
G. Smith, ed., Cambridge Encyclopedia of Geology, (New York: Crown Publishers,
1981, p. 269
Ophiolite is oceanic crust which is occasionally thrusted ontop of a continent
instead of going down.
Another citation is Thomas L. Wright, "Structural Geology and Tectonic
Evolution of the Los Angeles Basin, California," in Kevin T. Biddle, ed.
Active Margin Basins, American Assoc. Petroleum Geologists Memoir 52, (Tulsa:
AAPG, 1991), p. 44. Figure 6 shows the North American continent overriding
the subducting zone and covering the Farallon plate. The remnants are the
Cocos plate to the south and the Juan de Fuca plate to the north. Dickinson,
in 1970 used geochemistry of lavas to define an eastwardly dipping region from
which the volcanics came from. (see W. R. Dickinson, Relations of andesites,
granites, and derivative sandstones to arc-trench tectonics, Rev. Geophys.
Space Phys. 75:1619-1621.
So see, geophysicists expected some evidence of subduction prior to the
publication of van der Hilst's and Monastersky's article.
>
>>A comparison of the model (Figure 2) and the observations Figure 3
>
>Figure 2 is not a model. Figure 2 is "synthetic data calculated from
>assumed input models."
Synthetic data is a model. Beleive me I know what the geophysicists are
saying here.
>If cold slabs were 1300 km deep at the locations
>shown in Figures 2a and 2c, they and noise would alter seismic waves in
>certain ways. Inverting that "synthetic data" in a computer, gives the
>very sharp results shown in Figures 2b and 2d. Now compare the SHARP,
>NARROW images they got with artificial data to the FUZZY, WIDE images using
>real data (Figures 1b-1f and 3). This implies that what is really there is
>not a plate. Besides, who in their wildest dreams would have predicted
>plates there in the first place?
No, it just proves that nature is more complex than a model (or if you prefer,
synthetic data).
>
>>You have misinterpreted those two figures. For anyone who wants to go see
>>these pictures, realize that colder material has a faster velocity. Since a
>>subduction plate is still colder than the surrounding material it should
>>have a faster velocity.
>
>Relatively fast seismic velocities at certain points in the mantle MAY mean
>the rock there is relatively cold. Mineralogy variations or phase changes
>could also be an explanation. In other words, colder rock will speed up
>seismic waves, but fast seismic waves do not mean the rock was colder.
>Your calling it a colder region is one possible interpretation, not a
>measurement. For a complex set of reasons which I will skip for now, I
>suspect fast = cold, but let's not overlook that hidden assumption you and
>many others make.
It is interesting that the fast material points to the trenches as one goes
from deep to shallow.
>Even believers in the mythical "Tethys Sea and Tethys margin," don't claim
>they extend beyond the Mediterranean area. Your comment about the eastern
>Europe to Indonesia anomaly being "consistent with subduction along the
>Tethys margin," is a POSTdiction, not a PREdiction. Can you cite a
>prediction that a plate should be there? It is always easy, once you make
>a surprising measurement, to restructure a flexible theory to fit the data.
>
Sorry, Walter, this is not at all the truth. Long before the van der Hilst et
al article (April 1997) people have known about Tethys AND that it extended
far beyond the Mediterranean region. Articles like:
M. G. Audley-Charles, "Evolution of the southern margin of Tethys (North
Australian region) from Early Permian to late Cretaceous," in Audley-Charles
and A. Hallam editors, Gondwana and Tehtys, (Oxford Univeristy
Press/Geological Society) Special Publication No. 37, (1988) clearly show that
geologists beleived that the Tethys extends far beyond the Mediterranean.
The maps on page 158 of that book clearly show the Tethys extending into
eastern Asia.
In 1967 Mehderatta wrote of the Geology of India:
"The Keuper series is the uppermost member of the Triassic system and is the
thickest of all, being 2,800 feet. The lower part of the series is composed
of shales and marls and the upper of thickly bedded hard and compact
limestones and dolomites. The shales and marls correspond to the Carnic stage
and the limestones and dolomites to the Noric stage of the Alps. The Tethys
evidently had a very wide extent stretching as far as the Alps and beyond."~R.
C. Mehderatta, Geology of India, Pakistan and Burma, (New Delhi: Atma Ram &
Sons, 1967), p. 97.
The geology has said that India was once connected to Gondwanaland, the former
southern continent. The movement of India into Asia closed the Tethys sea.
Thus, this is not a postdiction, but a prediction. See Don and Maureen
Tarling, Continental Drift, 1971, pp 87-90. See also R. C. Mehderatta, Geology
of India, Pakistan and Burma, (New Dehli: Atma Ram and Sons, 1967), p. 79.
This was LONG before the article we are discussing.
I erroneously wrote:
>>The only anomaly is the faster Velocity along the East coast of the
>>US which may be due to deep, cool roots of the Appalachian mountains.
>
I was wrong. This is part of the subducting plate which was cut off when
North America covered the subduction zone.
This is how you will know I have retracted something. I will admit that I was
wrong. On the issue of your math, if I were to retract my objections, I will
clearly write something like this.
>Figure 5a can only be interpreted loosely as a subducting plate. I agree
>that on one vertical plane they found a diagonal fast region. But notice
>how thick and irregular the diagonal region is.
See also the same type of dipping faster region under North America in Science
News, July 19, 1997, p. 46.
So what if the slab is thick and irregular. What law says it must be sharp?
A slab at 1350 km has had time to partially melt. It is still colder and
faster than the surrounding material, but it has begun to spread out.
> Figures 5b and 5c, using
>"synthetic" or artificial data, show what a subducting plate should look
>like. Figure 5a, presumably the best example the authors could find in the
>world, doesn't look like a subducting plate should. Although the fast
>region points up toward a trench in the pictures we are shown, it falls
>short of connecting with the trench by at least 500 kilometers.
The method of seismic tomography becomes less accurate as one goes to the
shallower part of the earth. The reason is that one needs earthquakes to
measure velocity and there are fewer with the correct travel paths.
>Issue #5: The Alaskan Earthquake. You referenced an article on the Alaskan
>earthquake [George Plafker, "Tectonic Deformation Associated with the 1964
>Alaska Earthquake," _Plate Tectonics and Geomagnetic Reversals_ edited by
>Allan Cox (San Francisco: W. H. Freeman and Company, 1973), pp. 311-331.]
>Some of your statements must be answered.
>
>>Subduction is really nothing more than
>>a continent overthrusting the ocean floor.
>
>No, it's not.
Subduction is an overthrust. The continental crust or other oceanic crust
overrides the lowermost plate. This is exactly what happens when one rock
rides over another in the continental overthrusts. Only the scale is
different.
> Subduction, if it could happen, would be the slow diving of
>a lithospheric plate hundreds of kilometers into the mantle. Friction
>would act on both the bottom and TOP of the plate. The plates are
>typically 30-50 miles thick, hundreds or thousands of kilometers wide, and
>thousands of kilometers long. The leading face of the plate would
>experience incredible drag, since rock has to be pushed out of the
>way--somewhere. Also, buoyant forces would tend to lift the plate.
>Remember isostasy?
Yes, and remember that the Alaskan Earthquake uplifted an area of about 60,000
square kilometers. It happened before your eyes. Like aeronautical engineers
who used to say that mathematics showed that the bumblebee couldn't fly, the
bumblebee kept flying. Similarly, regardless of your math, the observational
evidence supports the long-distance transmission of motion and uplift imparted
by an earthquake. By ignoring Bernoulli's equation, I could find mathematics
which would say that airplanes can't fly also. Your math ignores the increase
in strength as materials are under more confining pressure.
>
>In contrast, overthrusting requires a relatively short, narrow, and thin
>slab to break from or somehow separate from its foundation. Once rapid
>movement begins, friction acts on only the bottom of a nearly horizontally
>moving plate. Relatively little drag acts on the front of the slab.
Not so if one speaks of the lower slab which is being pushed under. The same
amount of friction applies to it as to the subducting plate.
>Displacements are orders of magnitude less than that visualized in
>subduction.
So? You say that overthrusts are impossible. However, if we can actually SEE
motion on the subduction plate which IS an order of magnitude larger than most
thrust zones, what is the problem with having the smaller overthrusts move.
If we see motion on the larger system with no problem, then it most assuredly
will be able to occur on the smaller.
>
>>The asterisks [in Glenn Morton's sketch] mark the
>>subducting oceanic plate boundaries and the overlying
>>region is the continent overthrusting the oceanic plate.
>
>There is no basis for concluding that a subducting plate was involved in
>the Alaskan earthquake, even if you have drawn a picture. Had there been
>subduction, the continental region would have risen (and shortened).
It did rise 2-8 meters in that one earthquake. (See Plafker, Tectonic
Deformation Associated with 1964 Alaska Earthquake Science 148:1675-1687. It
also crumpled the coast into an S-shaped curve. Behind the region of 8 m. of
uplift was a region of 2 m depression.
The old surface looked like:
A-------------------------------------B
The new surface looked like:
8 --
6 -- --
4 -- --
2 -- -- new old
0 -- -- --B<-------B Difference is amount of shortening
-2 ------
The old surface was crumpled an now occupies a shorter distance. Since you
think this kind of foreshortening and uplift would be evidence of subduction,
I presume you are willing to admit that this is evidence of subduction.
>fact, it subsided (and lengthened by 2.7 meters). Plafker, the article's
>author, said as much on page 330. "The most serious limitation of the
>thrust-fault hypothesis lies in its attempts to account for the observed
>subsidence to the north of the zone of uplift." If you insist on a
>subducting plate being involved, then you should conclude that it slid up
>and out from under Alaska, allowing the continental region to sink. More
>seriously, because so much land rose to the southeast and sunk in the
>northwest, a major conclusion should be that mass shifted from the
>northwest to the southeast. That is just the opposite of what plate
>tectonics would predict.
Walter, you are selectively quoting. Let's look at a couple of things then
finish the quotation. You ever see a crumpled car after a head-on collision?
The very front of the car is pushed up from where it used to be and just
behind it, the car frame buckles downward or depresses. This is what we see in
the Alaska Earthquake.
Take a thin metal strip and bend it. You will see cracks develop on the outer
part of the bend. The cracks develop because the outer surface must now
stretch a longer distance than it used to. These cracks show expansion.
Similarly, Anchorage was near the location of maximum curvature on the
downwarped part of the earthquake. One should expect extension there and on
the surface of Montague Island where the land was uplifted the most.
Now with that in mind lets finish the quotation.
"The most serious limitation of the thrust-fault hypothesis lies in its
attempts to account for the observed subsidence to the north of the zone of
uplift. The relative scarcity of large aftershocks within the zone of
subsience, except in the immediate vicinity of the epicenter of the initial
shock, is interpreted as indicating that this zone was largely outside the
area of the primary fault rupture along which the earthquake occurred. In the
absence of surface-fault displacement, it is tentatively suggested that the
subsidence may be a secondary effect resulting frm elastic deformation
immediately adjacent to the postulated zone of thrusting. Preliminary results
of resurveys of small portions of the tirangulation net within the zone of
subsidence near Anchorage show as much as 2 2/3 meters of horizontal
elongation with a north-south distance of 48 kilometers, indicating that
crustal extension could have been a significant factor in producting the
observed subsidence.
"The hypothesis outlined above is generally consisstent with most modern
theories which relate arc structures in the circum-Pacific region and
elsewhere to master thrust faults along the unstable interface between the
oceanic and contiental crusts. it can also account for the following observed
features: (i) the areal distribution of the major zones of uplift and
subsidence; (ii) the marked asymmetry in the volumes of uplift and subsidence
in the two major zones; (iii) vertical or reverse surface faults in the zone
of uplift with up-to the north displacement; (iv) occurrence of the belt of
major aftershocks mainly within the zone of uplift and its inferred offshore
extension; (v) the shallow depths of the initial shock and aftershocks and the
tendency toward deepening of aftershock hypocenters beneath the continent;
)vi) the gologic record of late Cenozoic folding, reverse faulting and net
uplift of the continental margin and shelf, in contrast to the history of
relative stability or slight subsidence in the adjacent areas to the north.
(p. 330-331)
and finally
"It is postulated that the earthquake is genetically related to the
Aleutian Arc and probably resulted from regional compressive stresses oriented
roughtly normal to the Arc." p. 331
More recently, Le Pichon et al write:
"In Fig. 89B, a case of thrust faulting is shown. The deformation is given
with respect to the initally undeformed surface (in thin lines). Note that
seismic movements result in a general uplift on the overriding side of the
fault followed by a subsidence further away. Such an uplift on the innward
side of the fault, followed by a subsidence (both movements being accompanied
by horizontal movements0 is characteristic of the great earthquakes associated
with thrust faulting." Le Pichon et al, Plate Tectonics, (New York: Elsevier
Scientific Publishing com. 1973), p. 249
The earthquake fits a compressive, subducting regime. And a subduction zone is
an overthrust.
>The focus was 20-50 km deep. No clearly defined Benioff zone is shown.
>You are treating locations of aftershocks from the 1964 earthquake as if
>they were epicenters of many earthquakes.
You don't define a Benioff zone from 1 earthquake. It takes lots of
earthquakes. Many aftershocks have nothing to do with a Benioff zone. They are
the result of the shallower crust trying to adjust to the new stress field.
And by the way, Benioff did show a Benioff zone under the Aleutians. (See
Benioff, Orogenesis and Deep Crustal Structure," Bull. GSA 65:385-400, cited
in Cox ed. Plate Tectonics and Geomagnetic Reversals, ((San Francisco: Freeman
, 1973), p. 300
I am not going to follow your suggestion to keep it bite sized. If you put
out lots of objections all at once, it is my right to respond to them all at
once. If you wish to keep it bite sized, then you choose one issue and reply
to it.
glenn
Foundation, Fall and Flood
http://www.isource.net/~grmorton/dmd.htm
Douglas Cox
On 17 Aug 1997 "James J. Lippard" <lip...@primenet.com> wrote:
<snip>
[Glenn wrote:]
>>Subduction is really nothing more than
>>a continent overthrusting the ocean floor.
[Walt responds:]
>No, it's not. Subduction, if it could happen, would be the slow diving of
>a lithospheric plate hundreds of kilometers into the mantle. Friction
>would act on both the bottom and TOP of the plate. The plates are
>typically 30-50 miles thick, hundreds or thousands of kilometers wide, and
>thousands of kilometers long. The leading face of the plate would
>experience incredible drag, since rock has to be pushed out of the
>way--somewhere. Also, buoyant forces would tend to lift the plate.
>Remember isostasy?
>In contrast, overthrusting requires a relatively short, narrow, and thin
>slab to break from or somehow separate from its foundation. Once rapid
>movement begins, friction acts on only the bottom of a nearly horizontally
>moving plate. Relatively little drag acts on the front of the slab.
>Displacements are orders of magnitude less than that visualized in
>subduction.
Such displacements, producing structures known as overthrusts, would
be expected to occur during uplift of thick sediment piles, such as
those typical of many mountain areas, at the end of the flood. Slabs
of partially consolidated sediment would probably slide downslope over
other sediments, away from uplifted areas, where fluid sills or
unconsolidated layers were present in the sediments.
On the question about whether or not the alleged subduction process is
real, S.W. Carey, (prof. emer. University of Tasmania), leading
advocate of the earth expansion theory, says: "Subduction is a myth".
As well, David R. Oldroyd repoted:
According to Carey (pers. comm., 5 March 1994), the
National Aeronautics and Space Administration (NASA)
has been making measurements between Easter Island
and Peru. According to plate-tectonic theory, there is
only the Andean subduction zone between, and the
intervening distance should be decreasing. By earth-
expansion theory, it should be increasing. The results
were not made available to Carey by NASA (in 1992) as
they were thought to be 'anomalous'. Search was under
way for a hitherto undetected spreading zone in the
area. The situation was intriguing, to say the least.
Reference:
David R. Oldroyd, 1996. Thinking About the Earth, Harvard University
Press, Cambridge Mass., p. 344.
--
Douglas Cox
http://www.sentex.net/~tcc
Douglas Cox
In article <5t7ooh$1...@nntp02.primenet.com>, lip...@primenet.com says...
[Glenn Morton <grmo...@ns.waymark.net> wrote]:
>>If you study the hydroplate theory you will see that one common element in
>>the proposed mechanisms for overthrusting and mountain building is vast
>>quantities of water acting as a lubricant.
>As I noted before, water is NOT a lubricant for faults. it actually increases
>friction. let me quote this again. You obviously didn't see it.
>"Concerning the lubricating effect of water, Terzaghi (1950, p. 91) has shown
>that water definitely is not a lubricant on rock materials, and its presence,
>if anything tends to increase the coefficient of friction"~M.K. Hubert and
>W.W. Rubey, "Role of Fluid Pressure in Mechanics of Overthrust Faulting,"
>Bulletin Geol. Soc. Amer., 70, February, 1959, p. 129.
Glenn, have you ever heard of the beer-can experiment? You take a can of
beer, and put it on a piece of window glass sloped at an angle to the
horizontal (try about 30 degrees to start). When the bottom of the can
is dry, if the angle is right, the beer can does not slide, but wet the
bottom, and it begins to slide down the glass!
Could this mechanism apply here?
GRMorton
In article <5t82ai$c...@drn.zippo.com> you write:
>In article <5t7ooh$1...@nntp02.primenet.com>, lip...@primenet.com says...
>[Glenn Morton <grmo...@ns.waymark.net> wrote]:
>
>>>the proposed mechanisms for overthrusting and mountain building is vast
>>>quantities of water acting as a lubricant.
>
>>friction. let me quote this again. You obviously didn't see it.
>
>>"Concerning the lubricating effect of water, Terzaghi (1950, p. 91) has shown
>>that water definitely is not a lubricant on rock materials, and its presence,
>>if anything tends to increase the coefficient of friction"~M.K. Hubert and
>>W.W. Rubey, "Role of Fluid Pressure in Mechanics of Overthrust Faulting,"
>>Bulletin Geol. Soc. Amer., 70, February, 1959, p. 129.
>
>Glenn, have you ever heard of the beer-can experiment? You take a can of
>beer, and put it on a piece of window glass sloped at an angle to the
>horizontal (try about 30 degrees to start). When the bottom of the can
>is dry, if the angle is right, the beer can does not slide, but wet the
>bottom, and it begins to slide down the glass!
>
>Could this mechanism apply here?
Douglas,
Certain clays and clay minerals swell when they get wet. The swelling acts to increase the local pressure field,
which in turn tends to lock up the fault. Water lubricates beer cans, but not rocks.
Mark Isaak
>not stay collected under a horizontal plate for millions of years, or
>several days for that matter.
>
Steve Geller
First of all, I'd like to know why all the measurements of seismic
waves bouncing around within the earth, haven't detected Brown's
water reservoir.
As to subduction, the Pacific Coast, where I live, has an impressive
chain of volcanoes just east of where the Pacific Plate is thought to
be going under the North America Plate. Besides that, there are all
those "plutons" -- big bubbles of beautiful smooth granite, which one
sees high in the Sierras. Maybe water did that somehow? Some water
would have been included in a subduction too. We have a lot of
Serpentinite scattered all over the coast; it's basically squeezed
seabottom mud; it is very slippery.
Anyhow, if the water is still there, and still lubricates continents,
shouldn't we have another Great Flood any day? Why not, Dr. Brown?
Archae.S...@zippo.com
In article <5t82ai$c...@drn.zippo.com>, t...@sentex.net says...
>In article <5t7ooh$1...@nntp02.primenet.com>, lip...@primenet.com says...
>[Glenn Morton <grmo...@ns.waymark.net> wrote]:
>>>If you study the hydroplate theory you will see that one common element in
>>>the proposed mechanisms for overthrusting and mountain building is vast
>>>quantities of water acting as a lubricant.
>>As I noted before, water is NOT a lubricant for faults. it actually increases
>>friction. let me quote this again. You obviously didn't see it.
>>"Concerning the lubricating effect of water, Terzaghi (1950, p. 91) has shown
>>that water definitely is not a lubricant on rock materials, and its presence,
>>if anything tends to increase the coefficient of friction"~M.K. Hubert and
>>W.W. Rubey, "Role of Fluid Pressure in Mechanics of Overthrust Faulting,"
>>Bulletin Geol. Soc. Amer., 70, February, 1959, p. 129.
>Glenn, have you ever heard of the beer-can experiment? You take a can of
>beer, and put it on a piece of window glass sloped at an angle to the
>horizontal (try about 30 degrees to start). When the bottom of the can
>is dry, if the angle is right, the beer can does not slide, but wet the
>bottom, and it begins to slide down the glass!
>Could this mechanism apply here?
No... since one would need to completely overcome confining
pressure so that the two fault surfaces are hydraulically
separated. The beer can in your analogy is floating on the
water and that is not what Hubert and Rubey are saying in
their paper. It is not free water it is pore fluid pressure.
In fact if you read the paper carefully you will notice that
they give reported values for pore fluid pressures in fault
zones under differential stress and it does not exceed
0.8-0.9 confining pressure, usually much less than that
(they also give a better beer can anology than yours).
And I believe they explain why that is the case and it
is that the rocks will brecciate if the pore fluid
pressure is high. For you see a pore fluid in a fault
zone does not act as a lubricant but is an effective
stress. Here is the equation as it applies to fault
surface:
t (shear stress at failure)= C(cohesion constant) + u (coeffecient
of friction)*(sigma(normal stress)- P(pore fluid pressure))
(sigma(normal stress)- P(pore fluid pressure)) is called a
effective normal stress.
Now this is off particular interest to a Mohr’s circle stress
analysis. On the first diagram (figure 1) a Mohr’s diagram is
presented, the vertical axis represents the shear stress on a
plane and the horizontal axis is the normal stress acting on
a plane which transects the principal stress plane containing
sigma1 (maximum principal stress) and sigma3 (minimum principal
stress) in figure 1a .
Figure1
^
| Shear Stress
|
Tensile | Compressive
|
| * Failure Envelope
| *
| *
| * +
| * + +
| * + +
|* + + Mohr Circle
* | + +
* | + +
* | + +
-------------|----------------------------------------------- Normal Stress->
| sigma 3 sigma 1
|
<----------------------------------
Effective stress (pore fluid pressure)
Necessary to overcome confining pressure
Figure 1a
\ shear plane
\ sigma1
\ |
\theta|
\ |
\ |
\ |
\ |
\|
------------\---------- sigma 3
|\
| \
| \
| \
| \
|
The half circle is the Mohr circle, which its diameter
represents the differential stress (delta sigma= sigma1-sigma3).
Each position on the circle represents the normal stress and
shear stress acting on a posible plane of orientation theta
from sigma1. The angle theta represent half the angular distance
from a line connecting the point on the Mohr circle and the
center of the circle and sigma1 on the horizontal axis
(figure 2). The line represented by the asterisks is a failure
envelope as defined by Coulomb failure criteria. If the
Mohrs circle touches that envelope the rock will fracture
and shear along a plane at an orientation of theta from
sigma1. In the diagram no fracturing or shearing is occurring
since the Mohr circle does not make contact with the failure
envelope. This is were a pore fluid pressure comes in... From
the above equation we see that normal stress is reduce by an
amount equal to the pore fluid pressure and that includes
both sigma1 and sigma3. Therefore the Mohr circle is shifted
to the left and towards the failure envelope thus pore fluid
pressure becomes an effective stress. And if the pore fluid
pressure is large enough it will shift it right into the
tensile field of deformation and completely on the other side
of the failure envelope... the rock will disintegrate by
extensional fracturing. This is what you are suggesting will
occur if you think that the fault surfaces are hydraulically
separated by pore fluid pressure. Remenber that confining
pressure increases by about 30 Mpa per km in crustal rocks.
The deeper a fault is the more that Mohr circle is shifted
in order to overcome confining pressure by pore fluid
pressure.
Figure 2
^
| Shear Stress
|
Tensil | Compressive
|
|
|
| shear and normal stress on plane at angle theta from sigma1
| \ +
| + \ +
| + \ +
| + \ + Mohr Circle
| + \ +
| + \ 2 theta +
| + \ +
---------|------------------------------------------------ Normal Stress ->
| sigma 3 sigma 1
|
Now in the third diagram (figure 3) we see another curve
below the failure envelope. This curve represents the shear
and normal stresses acting on a pre-existing plane necessary
to cause shearing. Wherever the Mohrs circle touches that
curve a fracture (if it exists) at that orientation will
begin to shear. This is what Hubert and Rubey and other
researchers are saying in their papers... that a small pore
fluid pressure shifts the Mohr circle by a small amount so
that the pre-existing fault surface shears not so that the
pore fluid pressure is so high that the fault planes
separate and the rock disintegrates. From the diagram we
can see that high differential stresses are not very likely
as well (and this is generally an indication of the strain
rate... fast strain rate=high differential stress) for the
rock will also brecciate and disintegrate.
Figure 3
| Shear Stress
|
Tensile | Compressive
| Failure Envelope
| *
| * initiation of
| * ~ shear on pre-existing
| * ~ + facture surface
| * ~ + +
| * ~ + +
|* ~ + + Mohr Circle
* |~ + +
* | + +
* | + +
-------------|----------------------------------------------- Nornmal Stress
| sigma 3 sigma 1
|
<------
Effective stress (pore fluid pressure)
nessesary to initiate shear on a pre-existiong
fracture surface
High pore fluid pressure, high differential stresses and fast
strain rate all make rock very very very very brittle. This
hydroplate theory is nonsense on a basis of simple rock mechanics
that Brown claims is rarely investigated. This is completely false
since any modern structural geology textbook usually have a
detailed section on effective stress.
Archae Solenhofen (jmca...@gtn.net)
Mark Isaak
In article <33f7cb8c...@199.4.94.14>,
Steve Geller <sge...@dsp.net> wrote:
>First of all, I'd like to know why all the measurements of seismic
>waves bouncing around within the earth, haven't detected Brown's
>water reservoir.
According to Brown's theory, the water isn't there anymore. It all
came to the surface at the time of the Flood.
Douglas Cox
In article <5taqt9$1...@drn.zippo.com>, Archae.S...@zippo.com
(jmca...@gtn.net) wrote:
>>>>If you study the hydroplate theory you will see that one common element in
>>>>the proposed mechanisms for overthrusting and mountain building is vast
>>>>quantities of water acting as a lubricant.
>>>As I noted before, water is NOT a lubricant for faults. it actually increases
[...]
Well, thanks for the explanation of the Mohr failure theory, but in
the case of the beer can sliding down the glass, brittle failure does
not occur; as you say, the can floats on the water. I suggest
something similar might have happened briefly in past conditions, when
thick sediment piles were not yet fully consolidated, during the
compaction process. After the accumulation of thick piles of sediment
in the flood, for example, and associated with de-watering of
sediments, sills of fluid could briefly form, that "floated off"
overlying sediments.
A mechanism for the formation of fluid sills is described in the book
"Fluids in the Earth's Crust" that you mentioned in one of your
previous responses. In that book, (I think it is chapter 11) it is
suggested that such "fluid sills" may have formed in sediments, and
emptied, perhaps without even leaving a trace. These would be fluids
at lithostatic pressure, that formed an "underground lake". The
overlying sediment was supported by the fluid sills, just as in the
case of the beer can that slides down the glass. If there were uplift
of sediments that contained such sills, on the scale of uplifts that
resulted in the formation of mountains, a lot of lateral displacement
of sediment, or overthrusting might occur. The formation of fluid
sills such as this in past catastrophic conditions seems especially
likely in my Subcrustal Ice Earth Model (SIEM), which also provides a
mechanism for the uplift, by hydraulic pressure in subcrustal
conduits. Subsidence in one area caused uplift in another.
Now, perhaps some of the the large-scale overthrusts in mountainous
areas are actually evidence for the accumulation of these fluid sills
containing pressurized water, and for fluid-supported, unconsolidated
sediments sliding around during tectonic movements that occurred
during the compaction of sediments; this was followed by
lithification. Once the sediments became lithified, and uplifted, and
eroded, and the rock had become brittle, such movements would no
longer occur.
This fits the idea of rapid sediment accumulation and compaction of
thick piles of sediment at one time; it does not, however, fit very
well with the standard uniformitarian model that has sediment layers
forming and being compacted over long time spans.
Archae.S...@zippo.com
In article <33f97347.44774827@news>, t...@sentex.net says...
>In article <5taqt9$1...@drn.zippo.com>, Archae.S...@zippo.com
>(jmca...@gtn.net) wrote:
<SNIP>
No... a pre-existing fracture surface is activated in your
analogy. That is the normal stress acting on the beer/glass
interface was reduced significantly so that shear was possible
on the beer can/glass fault surface. I believe I mentioned
the activation of pre-existing fault surfaces by effective
stress in my post. Mohr’s applies here too.
> I suggest
>something similar might have happened briefly in past conditions, when
>thick sediment piles were not yet fully consolidated, during the
>compaction process. After the accumulation of thick piles of sediment
>in the flood, for example, and associated with de-watering of
>sediments, sills of fluid could briefly form, that "floated off"
>overlying sediments.
Mohrs circle still applies here as well. Confining pressure
is still needed to be overcome and then some in order to
“float off” overlying sediments. Brittle behavior still
applies to sediment under confining pressure. Do you think
unlithified sand at 100 MPa (3km depth) of confining pressure
is not solid.
>A mechanism for the formation of fluid sills is described in the book
>"Fluids in the Earth's Crust" that you mentioned in one of your
>previous responses. In that book, (I think it is chapter 11) it is
>suggested that such "fluid sills" may have formed in sediments, and
>emptied, perhaps without even leaving a trace.
The key word there is “perhaps”. If the rock has any
sedimentary structure it will be strained from the
intergranular deformations mechanism associated with soft
sediment deformation. If the strian is high this should
be very noticeable to anyone looking at these rocks after
they have lithified and exposed at the surface by erosion.
No geologist will dispute the presence of fluid
overpressure and the role it plays in deformation. The
problem lies in your notion of strain rate... which you
claim is very very fast. The problem in grain boundary
sliding is point contacts between neighboring grains and
point contact stresses are enormous in rocks at depth.
Point contacts are strain hardeners and must be overcome
by processes such as grain reorientation due to shear stress
or by cataclasis. The point contact stresses are very much
greater than that of confining pressure. As a result pore
fluid at lithostatic pressure is not going to allow the
sediments to flow away like they do on the surface.
The process is going to be very very slow at differential
stresses and pore fluid pressures low enough not to induce
faulting and extensional fracturing in the sediments (which
would also be very noticeable).
>These would be fluids
>at lithostatic pressure, that formed an "underground lake".
That’s pore fluid not as free water. There is a difference.
>The
>overlying sediment was supported by the fluid sills, just as in the
>case of the beer can that slides down the glass. If there were uplift
>of sediments that contained such sills, on the scale of uplifts that
>resulted in the formation of mountains, a lot of lateral displacement
>of sediment, or overthrusting might occur.
What like a decouplement fault/gravity slide? The stress
in a decouplement faults is mostly extensional. Please
present evidence that the formation of mountains is dominated
by a stress field that was extensional any time in its
deformational history. Strain is recorded in the rocks
that are deformed both at the macroscopic and microscopic
fields and pre-existing strain structures are generally
superimposed by the strain structures that follow. This
is called a strain history. Do you actually think that
all this occurs and does not leave any trace of its
existence in the deformed rocks? The geometry and kinematics
of mountain belt folds and faults and their structural
elements all indicate horizontal axial compression as the
dominant stress field.
>The formation of fluid
>sills such as this in past catastrophic conditions seems especially
>likely in my Subcrustal Ice Earth Model (SIEM), which also provides a
>mechanism for the uplift, by hydraulic pressure in subcrustal
>conduits.
You missed it.... I will say it again high pore fluid
pressure, high differential stresses and fast strain rate
all make rock very very very very brittle. This is clearly
demonstrated in the Mohr diagram. The differential stresses
the fluid pressures need to keep the Mohr circle within
the feild of stability for the most part. your theory has
high pore fluid pressure and high differential stress and
fast strain rate... Why is not all rock disintergrated?
> Subsidence in one area caused uplift in another.
>Now, perhaps some of the the large-scale overthrusts in mountainous
>areas are actually evidence for the accumulation of these fluid sills
>containing pressurized water, and for fluid-supported, unconsolidated
>sediments sliding around during tectonic movements that occurred
>during the compaction of sediments; this was followed by
>lithification.
Particulate flow, a form of grain boundary sliding under pore
fluid pressure, allows for the formation of soft sediment
deformation structures. The deformed sediment will preserve
these structures when they lithify. I do not believe we see
overwhelming evidence of soft sediment deformation in these
rocks... if you have evidence of this then now is the time
to present it.
On the otherhand, for example, we can look at the nappe
structures of the Helvetic region of Switzerland which show
very interesting characteristics. For example they are
metamorphosed showing increasing grade from the center of
the zone to the west and east. The limestone matrix is
strongly deformed. Universal stage and X-ray goniometer
texture determination show strong preferred crystallographic
orientations (pco) in c-axes and e-twin planes of calcite crystals,
reflecting intragranular deformation in a specific stress field. Strong
preferred dimensional orientations (pdo) of the calcite grains
are also observed and are related to the pco. Slaty cleavage
is also observed and is structurally related to the observed
folding. Pressure solution cleavage is observed and also
structurally related to the folds. The limestones contained
strongly (plastically) deformed fossils (echinoids,
belemnites, ammonites, gastropods) as well as plastically
deformed pebbles, ooids and syntectonic fibers in veins and
pressure shadows. The rocks show large translation ductile
shear zones with characteristic pco and pdo fabric
structures.
Your model seem to be suggesting is a deformation by
particulate flow or superplasticity that represents steady
state flow dominated by intercrystaline sliding. The above
majority of structural characteristic of the Helvetic
nappes are not suggestive of either. Superplasticity only
occurs at very high temperature and particulate flow occurs
at low temperature under very high pore fluid pressure. Do
you not find it odd that a flowing unconsolidated or
partially consolidated fine grained limestone would show
extensive plastic deformation at the crystallographic scale,
but very little intercrystaline sliding ? I certainly do.
Your assumption that these rocks were deformed by rapid
tectonic uplift due to high pore fluid pressure in rock or
sediment has no basis in the mountains of Europe or the
rest of the world.
Gravity sliding at depth is also not rapid. In high
pore fluid pressure regime a trade off is obtained between
reduced frictional resistance and lowering of the rock’s
fracture strength. The rocks of the Swiss Alps are not highly
brecciated as would be the result of the enormous hydraulic
force necessary to rapidly produce the structure that you suggest.
> Once the sediments became lithified, and uplifted, and
>eroded, and the rock had become brittle, such movements would no
>longer occur.
So they do not occur today? Why would they not occur... from
the Mohr diagram all that is needed is a sufficiently high
differential stress or in combination with a effective stress
shift so that contact is made with one of the two envelopes.
That is all that is needed and this has been demonstrated
both in the lab and in the field.
>This fits the idea of rapid sediment accumulation and compaction of
>thick piles of sediment at one time; it does not, however, fit very
>well with the standard uniformitarian model that has sediment layers
>forming and being compacted over long time spans.
Well read again Fyfe’s book... If memory surves me right he
discuses a number of mechanisms for how this occurs in a
“uniformitarian” model.
Archae Solenhofen (jmca...@gtn.net
Steve Geller
On 19 Aug 1997 19:38:42 -0400, at...@best.comNOSPAM (Mark Isaak) wrote:
>>First of all, I'd like to know why all the measurements of seismic
>>waves bouncing around within the earth, haven't detected Brown's
>>water reservoir.
>
>According to Brown's theory, the water isn't there anymore. It all
>came to the surface at the time of the Flood.
I figured that. But then it went .... where?
If it didn't evaporate into space, it had to go back into Brown's
alleged reservoir in the rocks. If it did that, we really should
be able to detect it.
I realize Brown is a creationist. But he claims to be arguing
science. If so, he can't just speculate.
Mark Isaak
In article <33fc3478...@199.4.94.14>,
Steve Geller <sge...@dsp.net> wrote:
>>According to Brown's theory, the water isn't there anymore. It all
>>came to the surface at the time of the Flood.
>
>I figured that. But then it went .... where?
The waters (supposedly) became our present oceans, which were quite
shallow before the cataclysm.
I saw no mention of how they achieved their present salinity, while
the polar ice caps, which came from the same source, are not salty.
David L Evens
Douglas Cox (t...@sentex.net) wrote:
: In article <5taqt9$1...@drn.zippo.com>, Archae.S...@zippo.com
: (jmca...@gtn.net) wrote:
: >>>>If you study the hydroplate theory you will see that one common element in
: >>>>the proposed mechanisms for overthrusting and mountain building is vast
: >>>>quantities of water acting as a lubricant.
: >>>As I noted before, water is NOT a lubricant for faults. it actually increases
: >>>friction. let me quote this again. You obviously didn't see it.
: >>>"Concerning the lubricating effect of water, Terzaghi (1950, p. 91) has shown
: >>>that water definitely is not a lubricant on rock materials, and its presence,
: >>>if anything tends to increase the coefficient of friction"~M.K. Hubert and
: >>>W.W. Rubey, "Role of Fluid Pressure in Mechanics of Overthrust Faulting,"
: >>>Bulletin Geol. Soc. Amer., 70, February, 1959, p. 129.
: >>Glenn, have you ever heard of the beer-can experiment? You take a can of
: not occur; as you say, the can floats on the water. I suggest
: something similar might have happened briefly in past conditions, when
: thick sediment piles were not yet fully consolidated, during the
: compaction process.
What thick piles of sediment?
: After the accumulation of thick piles of sediment
: in the flood, for example, and associated with de-watering of
: sediments, sills of fluid could briefly form, that "floated off"
: overlying sediments.
: A mechanism for the formation of fluid sills is described in the book
: "Fluids in the Earth's Crust" that you mentioned in one of your
: previous responses. In that book, (I think it is chapter 11) it is
: suggested that such "fluid sills" may have formed in sediments, and
: emptied, perhaps without even leaving a trace. These would be fluids
: at lithostatic pressure, that formed an "underground lake". The
: overlying sediment was supported by the fluid sills, just as in the
: case of the beer can that slides down the glass. If there were uplift
: of sediments that contained such sills, on the scale of uplifts that
: resulted in the formation of mountains, a lot of lateral displacement
: of sediment, or overthrusting might occur. The formation of fluid
: sills such as this in past catastrophic conditions seems especially
: likely in my Subcrustal Ice Earth Model (SIEM), which also provides a
: mechanism for the uplift, by hydraulic pressure in subcrustal
: conduits. Subsidence in one area caused uplift in another.
: Now, perhaps some of the the large-scale overthrusts in mountainous
: areas are actually evidence for the accumulation of these fluid sills
: containing pressurized water, and for fluid-supported, unconsolidated
: sediments sliding around during tectonic movements that occurred
: during the compaction of sediments; this was followed by
: lithification. Once the sediments became lithified, and uplifted, and
: eroded, and the rock had become brittle, such movements would no
: longer occur.
Of course, the fault lines present in the structure of all overthrust
features always show clear evidence of the interface being a rock/rock
one, and never any indication of it being a mud/mud one.
: This fits the idea of rapid sediment accumulation and compaction of
: thick piles of sediment at one time; it does not, however, fit very
: well with the standard uniformitarian model that has sediment layers
: forming and being compacted over long time spans.
Which doesn't matter, since it assumes that the rocks in the world are
unlike the rocks actually are.
--
---------------------------+--------------------------------------------------
Ring around the neutron, | "OK, so he's not terribly fearsome.
A pocket full of positrons,| But he certainly took us by surprise!"
A fission, a fusion, +--------------------------------------------------
We all fall down! | "Was anybody in the Maquis working for me?"
---------------------------+--------------------------------------------------
"I'd cut down ever Law in England to get at the Devil!"
"And what man could stand up in the wind that would blow once you'd cut
down all the laws?"
------------------------------------------------------------------------------
This message may not be carried on any server which places restrictions
on content.
------------------------------------------------------------------------------
e-mail will be posted as I see fit.
------------------------------------------------------------------------------