Why does the sea floor move in strips?

First up, and right up front, I don’t know. There is no answer waiting at the bottom.

This is more “admiring the problem” than having an answer (with a bit of ‘what does it mean to us’ along the way).

So, looking at the Sea Floor, we notice the spreading zones. That is where new sea floor is made. Most of the sea floor is under 150 Million years (out of 4.5 Billion years) so this is a relatively fast process in geologic terms. Looking at the age of the rocks, we see “stripes” that get older the further you are from the spreading zone.

But, look just a bit more closely, and we notice that the stripes move in long strips that are of different offsets. The little stripes of rock of the same age in any one strip are not aligned with their neighbor… One has to wonder “Why?”…

Sea Floor Age and Spreading Zones

Sea Floor Age and Spreading Zones

Original Image

The wiki is not particularly helpful, just noting that the thesis is that the cold ends are subducting under their own weight (and one wonders why not subduct 1/2 way from California to Japan… it ought to be cooled off an is just as heavy then?)


The new oceanic crust is quite hot relative to old oceanic crust, so the new oceanic basin is shallower than older oceanic basins.
If the diameter of the earth remains relatively constant despite the production of new crust, a mechanism must exist by which crust is also destroyed. The destruction of oceanic crust occurs at subduction zones where oceanic crust is forced under either continental crust or oceanic crust.

So it takes 150 Million Years for the crust to cool and thicken as it slowly moves from California to Japan? Really? Something just doesn’t sound right… I’d be more inclined to believe a massive upwelling of magma in the middle, lateral transport on the spreading plume, and then decent of the other side of the large magmatic convection cell, with the crust just “along for the ride” (and while it might thicken some, not being the major transport system).

Today, the Atlantic basin is actively spreading at the Mid-Atlantic Ridge. Only a small portion of the oceanic crust produced in the Atlantic is subducted.

So they don’t cool down enough to sink in, well, in “forever”? … Again, something not quite right. Looks to me more like the crust subducts where the viscous drag on the plate from the sideward moving magma is greater than the force needed to shove it under a continent and when one place becomes ‘the weak link’ the other places don’t need to subduct but just push their continent along.

However, the plates making up the Pacific Ocean are experiencing subduction along many of their boundaries which causes the volcanic activity in what has been termed the Ring of Fire of the Pacific Ocean. The Pacific is also home to one of the world’s most active spreading centres (the East Pacific Rise (EPR)) with spreading rates of up to 13 cm/yr. The Mid-Atlantic Ridge is a “textbook” slow spreading centre while the EPR is used as an example of fast spreading. The differences in spreading rates affect not only the geometries of the ridges but also the geochemistry of the basalts that are produced.

Notice that the East Pacific Rise comes ashore under the Gulf of California next to Baja and runs under the Salton Sea on up part of California, then mysteriously reappears Off Shore near Eureka… It gets displaced “sideways” somehow from the Salton Sea out to sea…


Since the new oceanic basins are shallower than the old oceanic basins, the total capacity of the world’s ocean basins decreases during times of active sea floor spreading.
During the opening of the Atlantic Ocean, sea level was so high that a Western Interior Seaway formed across North America from the Gulf of Mexico to the Arctic Ocean.

Hmmm…. So plate tectonics changes the depth of the oceans and when actively spreading the sea level rises / sea volume decreases… Wonder if the “CO2 Climate Drives Ocean Depths” guys know that…

OK, enough general observation, back to those strips of stripes.

Look closely at the area off the coast of Baja California and one up toward Oregon. Notice that one “block” is offset from the neighbors on each side? Off the coast of Canada, things are moving fast. Very fast. Near California, not so much. But down around Baja it picks up again. (Then further south, slows again).

Notice the ‘neat edges’ between this strips? Each “block” has a distinct “edge” that lasts for hundreds of miles away from the spreading zone. Each strip is a unique entity and moves on its own schedule. (Do they always have the same differential? Or to they ‘take turns’ and play ‘catch up’ some times? One can only wonder…)

If we look at a close up of the fault system in California, we notice something interesting:

California Quake Map with fault lines marked

California Quake Map with fault lines marked

Original Image

Most of the fault lines run up / down along the length of the state. But just south of The Great Valley there is one big one that runs side to side. The Garlock Fault.

Geology

The Garlock Fault is believed to have developed to accommodate the strain differential between the extensional tectonics of the Great Basin crust and the right lateral strike-slip faulting of the Mojave Desert crust.

Unlike most of the other faults in California, slip on the Garlock Fault is left-lateral; that is, the land on the other side of the fault moves to the left from the perspective of someone facing the fault. In the case of the Garlock Fault, this means that the terrain north of the fault is moving westward relative to the terrain south of the fault, which is moving relatively eastward.

But we know that the “Great Basin” area is having “extensional tectonics” as the East Pacific Rise has been subducted under the continent… and this says that the middle area of California is moving West faster than the southern side… IF you click on that spreading zone image above to get a larger view, you will see that the place where the Garlock Fault is located is just about the same place as the line between the two “strips” or blocks of ocean floor come ashore…. and in that case, the very long term view is that the California strip has been lagging behind as the southern strip kept on moving…

My Speculation

So which is it? Is the middle of California moving faster, or slower, than each side? Is the Garlock Fault just an extension of that inter-strip boundary on land? (I think so). Did the middle of California “fall behind” as the EPR got subducted under California as an “easy slip under” only to now get “stuck” on the Rockies and start the hard work of splitting the Basin and Range area off of the rest of the continent? Finally warming and softening the land above enough to start playing “catch up” with the strips on each side? Or are we just seeing a momentary “move” of the middle while most of the time it’s NOT moving and the spreading zones on each side have faster runs? (Them not being encumbered by a continent to stretch out..)

Does the fact that the volcanoes on each side of that strip (in Washington and Mexico) are more active mean anything? Or will the ones near Mono Lake and down toward Death Valley wake up again as soon as this episode of faster spreading ‘pauses’? Is the Garlock due for a major movement any time soon?

The last significant ruptures on the Garlock were thought to be in the years 1050 A.D. and 1500 A.D.. Research has pinned the interval between significant ruptures on the Garlock as being anywhere between 200 and 3000 years depending on the segment of the fault.

So it has had two about 500 years apart, and we’re now at 1500+500= 2000 AD… yet they state the ‘period’ is variable from a couple of hundred to a couple of thousand years, so don’t plan on anything.

You can see it running from the lower right to the upper left at the base of the mountains in this image.

Garlock Fault at the base of the mountains / edge of the Mojave Desert

Garlock Fault at the base of the mountains / edge of the Mojave Desert

Original Image

At the end of the day, I just don’t know.

It looks to me like the “easy under” of California let the other parts of the spreading zone ‘get ahead’ and now the spreading zone is starting to ‘catch up’ with the middle moving at normal rates again (and a bit faster than the neighbor to the south). An interesting “Dig Here!” would be to find the matching place up north where that side of the strip joint comes ashore and see which way it is moving, and how fast. If that IS what is happening, then we ought to see more quakes on the Garlock in the future and we ought to see action “up north”. If we get volcanoes where this is happening most, then we ought to see volcanoes waking up again along that Dead Sea to Tahoe line. And I can’t help but wonder if the “offset” line runs right under the Sutter Buttes where a volcano popped up 6 million years ago “for no good reason”… and if we’re moving again, when might it have some more slip, weakness, and bit of a rumble? Or has the movement “moved on” to under Lassen and Shasta, where Lassen had a burp in about 1914…

I do note that in the following diagram, the “spreading zone” on the ocean floor next to the Juan de Fuca plate comes ashore with a trajectory that sends it more or less under the Sutter Buttes and on toward that Mono Lake, Owens Valley, Death Valley, Salton Sea arc of spreading zone. So is THAT where the “catch up” ought to be happening next? Or will the block just sort of bend as things think about it for a couple of million more years?

Cascadia Subduction Zone and the associated Spreading Zone

Cascadia Subduction Zone and the associated Spreading Zone

Original Image

While we don’t see much in the way of “sideways” faults on the California map in that area, the history written in the rocks at sea says “something moves”…

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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13 Responses to Why does the sea floor move in strips?

  1. E.M.Smith says:

    OK, well, I got a comment box to show up here, via using a different browser to change the settings. In that browser things look normal too.

    My guess is one of 2 things:

    1) I’ve accidentally done a “chord” of some sort via scratching my left elbow while rolling the mouse wheel when clickeing with my left thumb and changed some magic hidden setting… or…

    2) When I clicked on “ignore new upgrade available” this morning, that triggered the “activate time bomb in recalcitrant upgraders” feature…

    At any rate, as I’m “on the road” shortly (after fireworks) and using an entirely different browser / computer, I’m going to shut this one down and let it stew for an unknown number of weeks… Maybe then it will realize how wrong it was to be petty with me ;-)

  2. George says:

    As the North American plate rotates counter-clockwise, the Garlock fault is moving South relative to that strip. That would mean that a new fault should be forming North of the Garlock fault, and that is exactly what we are seeing happening now with the White Wolf fault:

    http://geology.about.com/library/weekly/aa071199.htm

  3. Scarlet Pumpernickel says:

    I just don’t get how these continents move around so quickly, so it moves like 2mm a year, but then mountains appear or continents move so far from each other in just millions of years? And if one side spreads more then another, why is the earth round?

    This expanding earth thing, is it possible it just goes in and out? What is the evidence against this theory?

  4. wolfwalker says:

    2mm per year is a very slow rate. Centimeters per year is more typical.

    Chiefio: But, look just a bit more closely, and we notice that the stripes move in long strips that are of different offsets. The little stripes of rock of the same age in any one strip are not aligned with their neighbor… One has to wonder “Why?”…

    I wonder if there’s a problem of scale here. On the chart you reproduced, that is. Some of these small-scale charts have a very bad habit of exaggerating certain details. I would like to see a very large-scale, highly detailed chart of the spreading pattern for the Mid-Atlantic Ridge — say, 1 cm = 100 km, or something like that. I think the lateral ‘striping’ effect would be far more subtle, and perhaps easier to understand and explain.

  5. John F. Hultquist says:

    I quick read and a quick comment. Busy today clearing hawthorns from fence rows. Consider the issue of stripes as related to the movement of curved surface layers on a sphere. The pieces can’t move in the same manner as the sun roof on cars so equipped.

    SEE:
    Plate tectonics on a sphere
    Rovert Maurer presents Tectonic Forces
    <> | Home
    Part 4 – Convection currents and plate movements

    Further problems arise when the circulation current system is extended to describe plate movements over the spherical surface of the earth.

    http://www.tectonic-forces.org/pt04.htm
    ———————

    One of the original papers is this:
    Mc Kenzie, D.; Parker, R.L. (1967). “The North Pacific: an example of tectonics on a sphere”. Nature 216 (5122): 1276–1280. Bibcode 1967Natur.216.1276M. doi:10.1038/2161276a0

  6. Scarlet Pumpernickel says:

    The other thing that does not make sense is oh the shape of each continent fits into each other. But this is not true, as the continental plate is actually underwater, so what you see above the water is not the true shape as the shelves go out to sea. So they don’t fit exactly into each other?

  7. Pascvaks says:

    In some respects, it is convenient to think of the Earth’s crust as the bark of a tree. Now if I can only find a spherical tree in wikipedia to link to, and if they only have a pic.. back in a minute..

    oh well, who needs a wiki pic.. use your imagination, you know what I mean by a spherical tree and what its bark would look like, right?
    ;-)

  8. The notion of a spherical tree bark is interesting; it’s worth exploring in a different context. Instead of tree rings, we’d have tree spheres, sort of.

    Even allowing for the maps’ projection issues, there does seem to be a current Southern Spreading going on in general.

    Related to this, somewhat:

    Was India really exactly in the opposite position from the Gulf of Mexico at the time of the K-T impact?

    ===|==============/ Keith DeHavelle

  9. R. de Haan says:

    Nice quake 06-JUL-2011 19:03:16 -29.31 -176.20 7.8 1.0 KERMADEC ISLANDS REGION

    I wonder if the “strips” triggered a tsunami.

    No, no tsunami.
    http://earthquake-report.com/2011/07/06/massive-earthquake-in-the-open-sea-far-away-from-populated-areas/

  10. “The new oceanic crust is quite hot relative to old oceanic crust,”.
    Probably a silly question but, is there an increasing heating effect sufficient to contribute to global warming?

  11. John F. Hultquist says:

    Ken McMurtrie
    “. . . is there an increasing heating effect sufficient to contribute to global warming?

    The “heating effect” is there but one must assume Earth has long ago adjusted with a mechanism to get rid of it – rock to water to atmosphere to space. While the current understanding of plate tectonics is relatively recent (popular publication in 1960s), the phenomenon is ancient.

    However, you use the word “increasing” and I wonder where that notion comes from. For instance, read about flood basalts:
    http://en.wikipedia.org/wiki/Flood_basalt
    I live quite close to ‘Moses Coulee’ used as the photo for this article.
    Also, note the links to Deccan Traps and Siberian Traps. If you want to read more detail, go to:
    http://en.wikipedia.org/wiki/Columbia_River_Basalt_Group

  12. @John.
    Fair comment! If the rate of exposure of new crust is unchanging, thermal stability would be maintained.
    My suggestion of increasing simply came from EM’s general thrust of changes being noticed and what seems to a current increased earthquake and volcanic activity.
    Terms like:
    “Today, the Atlantic basin is actively spreading at the Mid-Atlantic Ridge.”
    “The Pacific is also home to one of the world’s most active spreading centres…”
    “Does the fact that the volcanoes on each side of that strip (in Washington and Mexico) are more active mean anything?”,
    suggest that the activity is not at a steady rate.
    If so, heating effects may vary and may be a forcing factor in the alleged surface temperature changes over which some people seem to have their knickers in knot.

  13. E.M.Smith says:

    @John F. Hultquist and Ken McMurtrie:

    You must specify a “time scale” for “increasing” or “stable” to be “on the same page”. As with most cyclical things, it can be going both ways at the same time on different “scales”…

    So long term, the earth is cooling. One thesis has the nuclear rector at or core running out of sufficient U to react at any decent rate just about now… so very rapid (geologic scale) cooling to come compared to the last Billion years…

    Yet on a 1500 year time scale, there may well be a cyclical change that has now turned to “more active for a little while” compared to the last 100 years.

    Yet on a 6 month time scale, things were very active at the Supermoon, and have quieted a lot recently.

    Yet on a one day….

    So over 10,000 years, the earth is likely in balance with volcanism and plate spreading. BUT on a 100 year cycle, there could be a ripple that is moving toward more Right Now… Which is what I’m seeing.

    We’ve got less than a Billion years ago (by rather a lot), less even than a 100 Million years ago. Perhaps even less than 10,000 years ago. But more activity NOW than in 1990 (and a lot more than in 1913-4).

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