#Why Midwest Earthquakes
29 messages in this thread
While watching a news program the other night (I think it was Nightline), they
brought up the fact that earthquakes occur other places besides the West Coast.
They mentioned the Midwest. I recall reading about the "tremendous" New Madrid
earthquake in the early 1800s. Fortunately, that regions was thinly populated
back then, so there were not a large number of fatalities.
However, this raises a question. Since the Pacific Coast quakes occur in a
region where the oceanic plate is "subducting" the continental plate, it's
obvious that there would be quakes. But, how can you have quakes in the middle
of a continent, where there are not confrontations between two separate crustal
plates? Answers, anyone?
BTW, I'm not a geologist, just an amateur scientist.
Leland in (non-seismic) Houston
Leland
Heres my two cents
The remaining earths crust has major faulting some that penetrate down
to the base of the continental crust. All rivers follow these faults. All the
canyons were large cracks that opened up in the crust and the rivers just
follow the natural lowest points. The entire crust is floating on a series of
alternating levels of solid and liquid layers. Gravitational forces cause the
metals to gather in tides under the crust. At times the motions of these tides
has the rhythm and direction and magnitude to cause minor adjustments in the
faults. Therefore earthquakes can occur anywhere where there are major faults.
Kamron
Kamron,
> The remaining earths crust has major faulting some that penetrate down to the
base of the
> continental crust. All rivers follow these faults. All the canyons were large
cracks that opened
> up in the crust and the rivers just follow the natural lowest points.
_All Rivers_ ??? _All Canyons_ ???
Geez, Kamron, you sure know how to paint broad strokes. 🙂
Rivers occur anywhere water overfills a basin and continues to supply that
basin. Rivers can, and do, then proceed to cut canyons through erosive means.
I'm afraid I have to take exception to your painting style. Perhaps it's time
to say things like "In some cases…" or "perhaps…" eh?
Ben Williams
Suffering from an overdose of common sense
Ben
Never won awards for my style. And you are right some streams are overflows
of basins.
However most rivers do end up in the lowest areas which normally are faults.
Rock canyons for the most part were formed by splits in the Crustal plate.
Some are more obvious than others. The vertical wall canyons along the Rio
Grande north of Albuquerque and where she exits between cliffs in the Big Bend
area are perfect examples. Remove the infill from the bottom and the two sides
would fit back together perfectly.
The Grand Canyon is another large tear in the crust that can be traced all the
way to Baja. While the colorado has carried away some material out of the
canyon it didn't saw down as the mountain rose.
These faults were caused by a great catastrophe that ended the cretaceous
period and ripped and fractured the original crust which split into the
current continents. The missing crust became…………. the moon. Yes …I
said it. More bad style but worthy content presented poorly.
Kamron
Hi, Kamron–
>> The entire crust is floating on a series of alternating levels of solid and
liquid layers.
Seismic shear-waves (S-waves) cannot travel through liquid, yet they travel
through all of the Earth's crust and mantle – they are stopped by the core,
telling us that the outer core is liquid. They do not show us your layers.
>> All the canyons were large cracks that opened up in the crust and the rivers
just follow the natural lowest points
Shortly after you last claimed that about the Grand Canyon, I had a really good
look at it from an airliner window. You have clearly never looked that way at
the Colorado river just downstream of the G.C.; the canyon follows in loving
detail the meandering pattern we see in any shallow-grade river section. The
loops constantly miss intersecting each other by a tiny bit, leaving a thin bit
of plateau between them – and a much larger bit of plateau inside each loop,
connected only by the thin "isthmus" between loops to the main plateau. The
edges of the canyon parallel the river through every curve, maintaining a
constant width (if measured perpendicular to the river at every point).
There is _no way_ this could have been pulled apart in this pattern.
–Doug
Doug
I liked your description.
I would need to see the down river side to discuss it.
I have seen the Grand Canyon and it wasn't in my opinion cut by the river. The
GC has large butte like formations that sit in the canyon, the river would have
to alternate back and forth on each side of this type of structure how could
that occur? These are not all cut threw loop formations either. The deep side
canyons that have tiny streams would not have cut them the same speed as the
the Colorado. Why would it be so wide if it weren't fractured to smitherines?
Your thinking about the catastrophe though….it will make more and more sense
them more you think about it.
I was 12 when I first say the GC and I remember so clearly listening to the
Ranger as he described the layers of the earth. I asked where the material came
from that made the layers. He said it blew here from other places. That
furrowed my brow permanently.
Kamron
Hi, Kamron–
>> the river would have to alternate back and forth on each side of this type
of structure how could that occur?
Meandering rivers do that – study the Mississippi.
>> The deep side canyons that have tiny streams would not have cut them the
same speed as the the Colorado.
Not necessarily; it is not only the size of the stream but the speed of the
water and the amount of suspended hard grit that governs its cutting power. Let
the Colorado carve a V like we see downstream, then the tributaries will be
flowing rapidly down the side of the V, at terrific speed and cutting backwards
(away from the Colorado) as much as downwards.
>> I asked where the material came from that made the layers. He said it blew
here from other places. That furrowed my brow permanently.
Some layers blew in, some washed in. Your brow furrowed only because you
assumed the layers did not take tens and hundreds of millions of years to form
– given time, it is easy. We see probable future sandstones in a great many
sandy deserts, and see the wind marching the sands back and forth. They are
just waiting for some limy water or other cementing agent to arrive…
–Doug
Doug
>> Meandering rivers do that – study the Mississippi.<<
It is meandering in soil and sand. Moving back and forth around a rock tower
is a different story. The water seeks a short cut and once the river had cut
lower on one side of the tower it would never find it easier to return again
over the high side let alone do this over and over back and forth creating the
massive tower.
Kamron
Kamron,
>> The water seeks a short cut and once the river had cut lower on one side of
the tower it would never find it easier to return again over the high side let
alone do this over and over back and forth creating the massive tower. <<
Never? Never say never, Kamron — Nature has a funny way of proving such
claims wrong with monotonous regularity. <g>
Consider this scenario: River follows path of least resistance, and cuts a
valley or even a canyon in soft rock to one side of a tower of harder rock,
maybe an igneous intrusion. By and by, you have the river, then the igneous
tower, then sedimentary rock all round the rest of the tower.
Now you have an earthquake — say, a strike-slip type quake with most of the
motion horizontal. Say you get a big fracture right along the border between
the sedimentary rock and the igneous rock. Say that fracture leads into the
riverbed upstream and downstream of the igenous tower, and bottoms out just
below the upstream riverbed. Then the river, always following the path of
least resistance, will quit flowing on the one side of the tower and start
flowing on the other side. Allow another few million years for erosion, and
you wind up with the tower sitting alone with a river on one side and an empty
ex-riverbed on the other side.
Modify this scenario a bit, and you could easily get the river flowing on both
sides of the tower.
Jon W.
Jon
>>Never? Never say never, Kamron — Nature has a funny way of proving
such claims wrong with monotonous regularity. <g><<
Poor comm tech, Needs work huh? its better than nutin.<g>
>>Consider this scenario: River follows path of least resistance, and
cuts a valley or even a canyon in soft rock to one side of a tower of
harder rock, maybe an igneous intrusion. By and by, you have the river,
then the igneous tower, then sedimentary rock all round the rest of the
tower.<< I can buy this, the free standing mesas are a bit like that.
The Grand Canyon, correct me if I'm wrong has consistency in the layers. One
layer may be a different texture, density and material but the layer is very
consistent. So it is a different sit.
The carving of a canyon would maintain a V shape. How would you account
for vertical walls in a canyons?
Kamron
Jon
>>Never? Never say never, Kamron — Nature has a funny way of proving
such claims wrong with monotonous regularity. <g><<
Oh I did it again, poor conversational tech, I admit.
>>Consider this scenario: River follows path of least resistance, and
cuts a valley or even a canyon in soft rock to one side of a tower of
harder rock, maybe an igneous intrusion. By and by, you have the river,
then the igneous tower, then sedimentary rock all round the rest of the
tower.<< I can buy this, the free standing mesas are like that.
The Grand Canyon, correct me if I'm wrong has consistency in the layers.
One layer may be a different texture, density and material but the layer
is very consistent. So it is a different sit.
The carving of a canyon would maintain a V shape. How would you account
for vertical walls in a canyon?
Kamron
Hi, Kamron–
That stretch of the Colorado River I spoke of had nearly completed its first
rows of towers. It seems clear the river established a meandering pattern like
the Mississippi in the flat plateau, when it _was_ dealing with dirt and sand,
but then it cut into the plateau rock enough to fix the meanders in stone. Now
locked in a pattern, it just kept cutting. It is obvious that a little more
cutting will isolate what will then be towers – the canyon width is almost
enough to cut across the meander loops. The river will never have switched
sides relative to the tower; on one side of the tower the isolation will have
been by collapses of rock the river undercut, not by the river itself.
More than this must have happened to form the Grand Canyon, at least partly
because of tributaries and maybe weak areas in the bedrock, but this meandering
mechanism may have started it out.
Once it has cut the first canyon, the river can still change course if dammed,
especially if tributaries and such have created a partial route. For example,
it might cut into a soft layer, then cut sideways through the soft stuff,
causing the overhang to collapse and dam the river. It shifts a bit and
resumes undercutting… Say, this presents an alternate theory for the
meandering pattern. I suspect this undercutting trick could cause it to
generate meanders even after it has cut into the plateau. I prefer the
meanders-before-first-cutting theory, but the same asymmetry of speed-ups
feeding back to cause stronger asymmetries might work in undercutting mode.
–Doug
Doug
I anticipated the thinning neck of the meander situation as a comeback so I
excluded it …but I have not seen meanders in deep rock canyons. If the
colorado does this I need to see it for a verdict.
>> That stretch of the Colorado River I spoke of had nearly completed its
first rows of towers. It seems clear the river established a meandering
pattern like the Mississippi in the flat plateau, when it _was_ dealing with
dirt and sand, but then it cut into the plateau rock enough to fix the meander
in stone. Now locked in a pattern, it just kept cutting. It is obvious that a
little more cutting will isolate what will then be towers – the canyon width is
almost enough to cut across the meander loops. The river will never have
switched sides relative to the tower; on one side of the tower the isolation
will have been by collapses of rock the river undercut, not by the river
itself.<<
I need to look at the actual locations to discuss. I can see this explanation
as working but the towers should be at the sides of the canyon instead of the
middle.
>>More than this must have happenedto form the Grand Canyon, at least partly
because of tributaries and maybe weak areas in the bedrock, but this meandering
mechanism may have started it out.<<
I beleive there are only tributaries in one side of the canyon as I remember
.. is that the case? If this is so…. why, if the river started in a low
spot area would there not be traces of ancient tributaries comming into the
canyon from the other side also.
>>Once it has cut the first canyon, the river can still change course if
dammed, especially if tributaries and such have created a partial route. For
example, it might cut into a soft layer, then cut sideways through the soft
stuff, causing the overhang to collapse and dam the river. It shifts a bit and
resumes undercutting… Say, this presents an alternate theory for the
meandering pattern. I suspect this undercutting trick could cause it to
generate meanders even after it has cut into the plateau. I prefer the
meanders-before-first-cutting theory, but the same asymmetry of speed-ups
feeding back to cause stronger asymmetries might work in undercutting mode.<<
The meanders occur in valleys that have been infilled with sediments and
sands.I don't remember seeing any rivers creating a meandering pattern in deep
rock canyons.
Kamron
Kamron,
>> The meanders occur in valleys that have been infilled with sediments and
sands.I don't remember seeing any rivers creating a meandering pattern in deep
rock canyons. <<
They don't, not directly at least. Downcutting and canyons are indicative of a
young, fast-flowing river. Meanders and wide floodplains are indicative of an
old, mature river. However, if an old river establishes meanders and
floodplain, then the land it flows on is uplifted or tilted, it will start
flowing faster and will start downcutting again. My college Earth Sciences
text has a picture that illustrates this perfectly. It's a photo of a part of
the San Juan River in Utah. It shows the river with wide, sweeping meanders,
including one in which the upstream and downstream curves nearly meet and
there's an enormous peninsula with a very narrow neck. A perfect meander —
except that the riverbed is a canyon that looks to be a couple of hundred feet
deep, meanders and all.
These formations (meandering canyons) even have a name — they're called
entrenched meanders.
Jon W.
Hello Jon
>> It's a photo of a part of the San Juan River in Utah. It shows the river
with wide, sweeping meander, including one in which the upstream and downstream
curves nearly meet and there's an enormous peninsula with a very narrow neck.
A perfect meander — except that the riverbed is a canyon that looks to be a
couple of hundred feet deep, meanders and all. <<
Oh boy pictures tell a story. I'll take your word for it but still gotta see
it. I can see some cutting occuring but it takes a rare set of circumstances
for a canyon to get cut , and I guess I just haven't seen any.
All the vertical wall canyons so far would fit back together perfectly if the
two sides were somehow moved back together.
What is the book again that has that picture?
Kamron
Kamron,
You want it, you got it. The book is:
EARTH SCIENCE, 5th Edition
Edward J. Tarbuck & Frederick K. Lutgens
Merrill Publishing: 1988
The photo I was referring to is on p.80.
Jon W.
The Gooseneck of the San Juan is near Mexican Hat, Utah. It has been
photographed by a great many professional photographers and millions of
amateurs. You might look in the PHOTOFORUM and see if their is a GIF available
online. Another place to look would be in the books of Ansel Adams, John
Sexton, or Eliot Porter. I'm sure Adams and Sexton have published photos of the
Goosnecks.
BTW from down at the bottom, the opposite walls of the canyon look like they
would fit together very well except where the numerous side canyons, of which
there are hundreds, hide the symmetry.
jf
Hi, Kamron–
>> I can see this explanation as working but the towers should be at the sides
of the canyon instead of the middle.
From the river's viewpoint the towers-to-be are at the side of the canyon. But
if you draw lines parallel to the _general_ trend of the river tangent to the
meanders, you see a future canyon in which the towers are on the opposite side
of the centerline from their "side" as now seen by the river. If a boat in the
river sees a tower pass on starboard, a crow flying downstream along the
centerline of the whole shebang will see it on the port side.
>> I beleive there are only tributaries in one side of the canyon as I remember
.. is that the case?
I do not swear, but that is how I recall it.
>> why, if the river started in a low spot area would there not be traces of
ancient tributaries comming into the canyon from the other side also.
Low spots can be quite asymmetric. Let a general downtrend meet an anticline,
fault, or whatever…
From your message to Jon: >> The carving of a canyon would maintain a V shape.
How would you account for vertical walls in a canyons?
That depends on the rock involved. The more cohesive the rock, the steeper its
angle of repose, which I think is the main determinant of the classical V-shape
of a river-cut valley. But where other tricks come into play like
undercutting, less stable configurations steeper than the angle of repose may
be found.
–Doug
Doug
>>From the river's viewpoint the towers-to-be are at the side of the canyon.
But if you draw lines parallel to the _general_ trend of the river tangent to
the meanders, you see a future canyon in which the towers are on the opposite
side of the centerline from their "side" as now seen by the river. If a boat in
the river sees a tower pass on starboard, a crow flying downstream along the
centerline of the whole shebang will see it on the port side.<<
No doubt this can occur. The cutting process would have effected the curves
much more making them progressively wider than the straight sections and in
deep canyons this is no the case. I haven't seen the San Juan Gooseneck, sounds
very interesting and may be cutting but I still doubt cutting as the cause of
vertical wall canyons.
This does not take anything away from the traditional geological erosion
process as a workable planet forming process, I just think earth had a
different history.
>>Low spots can be quite asymmetric. Let a general downtrend meet an
anticline, fault, or whatever…<<
True but there should be small side canyons on both sides or there would be a
different set of layers on each side of the canyon which i believe isn't the
case.
>>The more cohesive the rock, the steeper its angle of repose, which I think
is the main determinant of the classical V-shape of a river-cut valley. But
where other tricks come into play like undercutting, less stable configurations
steeper than the angle of repose may be found.<<
Again this same process will widen the curves of a river if it was cutting a
canyon. The curves in many canyons have the same parallel features on both
sides, more or less. The curves are not wider than the straight sections.
Vertical wall canyons a classic being the Rio Grande north of Albuquerque is
where the fault creating the path for a river comes totally into focus. Have
you seen it?
Kamron
Hi, Kamron–
>> The cutting process would have effected the curves much more making them
progressively wider than the straight sections and in deep canyons this is no
the case.
I see no reason why curved sections should be wider than straight sections (I
would guess the opposite, since straight may mean faster-moving), unless you
are looking ahead to when entrenched meanders connect up.
>> True but there should be small side canyons on both sides or there would be
a different set of layers on each side of the canyon which i believe isn't the
case.
Given an asymmetric low, one side would collect water over a wide area (the
shallow downtrend) and dump it into the low, but the steep side would collect
very little water on the side of the low (the watershed is much closer to the
depression we speak of). No tributaries worth mentioning means no side canyons
worth mentioning.
If it is a fault scarp creating the asymmetry, the layers should indeed be
mismatched on either side. But if an anticline, that does not follow,
depending on how closely the river cut approaches the axis of the anticline,
and how much the anticline is folded – it could be very subtle. I am not sure
what sort of feature governed the asymmetry of the Grand Canyon; there are
surely other possibilities.
Indeed, given a shallow general downtrend, if a river crosses it rather than
flowing downwards (perhaps because the downtrend was established after the
river course?), it should create its own asymmetry of tributaries. Any water
on the upslope side will tend to flow to the crossing river, any water on the
downslope side will tend to flow away from that part of the river.
In the matter of creating vertical walls by undercutting, I agree the canyon
should be made wider than otherwise.
I have not seen the Rio Grande (I probably drove over it, but I was not aware
of it as the Rio Grande at the time).
–Doug
>> Seismic shear-waves (S-waves) cannot travel through liquid, yet they travel
through all of the Earth's crust and mantle – they are stopped by the core,
telling us that the outer core is liquid. They do not show us your layers. <<
Why would the shear waves not penetrate the liquid layers?
The pressures at those depths would give the liquids high densities that
should propagate the waves.
I don't understand the exact difference in the shear waves that would make
them not travel through high density liquids can you help me here?
If the inner core of the earth is composed of super dense pre-elemental
material that may not transmit the waves and the waves are transmitted through
the balance of the layers then the same results would occur.
Kamron
Hi, Kamron–
Pressure waves (P-waves) are like sound – alternate compression and
rarefaction of the medium. Solids, liquids and gases all expand when released
from compression.
Shear waves are side-to-side motions, like swinging one end of a garden hose
side-to-side and seeing the wave of sideways motion traveling down the hose.
Swing a bit of solid sideways, and it will pull the next bit of solid sideways,
which will pull the next, and so on. Meanwhile the first bit of solid will
generally "want" to snap back toward its original position (i.e., its effect on
the farther bit of solid has a reaction). But a fluid can move sideways
without the farther bits of fluid being much affected. Fluids have viscosity,
but that is trivial compared to the connection between parts of a solid, and
they do not snap back after a sideways motion – they will just stay where they
were moved, on average.
–Doug
Doug
Thanks for the data.
It isn't totally computing yet…I need to let it roll around the old noodle
some.
Kamron
>>>All rivers follow these faults. All the canyons were large cracks that
opened up in the crust and the rivers just follow the natural lowest points.<<<
Ah com'n Kamron. It's entirely true that some rivers and lakes follow fault
lines. California's Kern river for example clearly follows a fault across the
slope of the Sierra Nevada until it swings West to flow out into the Central
Valley. OTOH the Hudson, Lake Champlain Richelieu River System follow a normal
fault at the South End, but appears to be controlled by the leading edge of
hard Cambrian rocks thrust faulted over soft Ordovician rocks over much of it's
length. And the Mohawk river just follows the natural exposure of soft Utica
shales all the way from Herkimer to Albany.
Hello Don
Oh please let me extract the balance of my foot. POP!
Someday I will learn not to use words like all and always.
Most should be substituted for all.
My point though is….the faults occurred and the rivers flowed in them in
_most_ cases instead of the river carving the canyons.
The continents are covered by faulting going in all directions. These faults
were filled with rubble in many cases and in some cases were opened up and then
closed with the structural problem still intact.
Later the right gravitational stresses by the moon and sun can trigger
adjustments in the fault causing quakes.
Kamron
Leland,
Earthquakes can happen anywhere you have active faults in the bedrock. They
aren't limited to plate margins and volcanic regions.
No one is quite certain of the origin of intra-plate faults like the New Madrid
Fault. One school of thought holds that the New Madrid fault complex is a
"fossil rift," what's left of an area where the North American continent almost
split apart some 850 million years ago. The rift would have been similar to
Africa's Great Rift Valley. It didn't develop into a true rift the way the
Mid-Atlantic Ridge did, and it's certainly long dead, but the New Madrid faults
may be a remnant of that activity.
Jon W.
Jon,
FWIW, the Great Rift Valley is splitting apart, and (eventually) there will be
an ocean between the two parts of Africa on either side. In fact, the Red Sea
is already formed, and will get wider over the millions of years.
The "rift" is what geologists call a "graben" in which the crustal plate on
both side is pulling apart, with the strip in between sinking to fill in the
gap. At least, that's what I read in a popular-level geology book. In fact,
the entire Jordan Valley (including the Dead Sea) is part of this rift. That's
how come the Dead Sea is below sea level, since erosion alone could never cause
the interior regions to become lower than sea level.
Leland (amateur scientist) in Houston
Hi, Leland–
Some maintain that the rift valley may have ceased its rifting action, with
the newer main action being in the Red Sea and the Gulf of Aden. These rifts
are presumably worrying away at the "lock" in the Afar triangle, where they are
trying to meet.
–Doug
Leland-
The movement of the north american plate is not all released at the plate
boundary. There is stress throughout the plate and some can re released within
a plate. Another more interesting possibility is that there is actually a
plate boundary lurking around on the east coast. This idea is not all that
popular with the hard-core plate tectonic crowd. Try reading "In suspect
terrain' by George McPhee. He raises some interesting questions. Chris
Chris,
That McPhee fellow–his friends just call him John.
Nathan