Sea-Floor Sunday #3: Gulf of Mexico continental slope
The continental slope in the northern Gulf of Mexico has a very distinct appearance. Note the pock-marked nature in the water depths colored red in this bathymetric image below. The coastal area at the northern end of the image is the Mississippi delta of Louisiana.
The transition from the pock-marked slope to the smoother and lower-gradient abyssal plain (yellowish colors in image above) is a rather abrupt escarpment with nearly 1,000 m of relief.
Here’s another image of the GoM continental slope from a great Geology paper from over 10 years ago now by Pratson and Haxby (link to paper here). This is a perspective view looking towards the east. The black area in the upper left is the continental shelf.
The escarpment I pointed out above is clearly visible in this perspective image. Note the arcuate shape of the trend of this escarpment (called the Sigsbee Escarpment). If it reminds you of a thrust-front, that’s because it is!
The morphology of the GoM continental slope is dominated by salt tectonics. Jurassic evaporites have evacuated causing some areas to sink (the pocks, or “mini-basins”). That evacuation is balanced by salt diapirsm in other areas. Overall, the entire slope is affected by gravity and slowly moving towards the deeper part of the basin. The Sigsbee escarpment is the compressional front of that large-scale movement. In detail, each mini-basin is extraordinarily complex showing fascinating relationships between turbidite sedimentation and salt movement. A feedback is set up such that turbidites are deposited in the lowest parts (that’s what they do), which causes more underlying salt to evacuate, which in turn makes the basin subside, which maintains that spot being the lowest. Some mini-basins have 20,000 feet of Quaternary sediment in them!
There’s tons of information out there regarding the Gulf of Mexico. If you’re interested in more, you won’t have much trouble finding cool stuff.
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Check out this page (a professor at Colorado School of Mines) for more about salt tectonics, in general.
Top image from here.
See all Sea-Floor Sunday posts here.
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So which bits have oil in them?
it’s everywhere…sort of
most of the hydrocarbons that are in sediments above the salt have been discovered, and are being produced
the big unknown now is how much is hosted sub-salt … the big issue is that the salt wreaks havoc on seismic imageing … you just can’t see anything below that stuff, it’s all fuzzy
so, there are some very expensive holes ($100 million a shot!) being drilled just to find out … some of these wells are over 30,000 ft deep
Man, if somebody gave *me* a 100 million dollar drilling budget…
“Man, if somebody gave *me* a 100 million dollar drilling budget…”
They’d expect you to find something worth $100,000,000.01
How can I find imagry of the bottom in a certain area. I am a fisherman in Mississippi. If I could find bathymetric imagery or multi beam mapping of a certain area it would help tremendously. Any type of bottom mapping would really help. If anyone would know how to get this information please let me know.
Steven,
As far as I know, there’s no one place to find all sea-floor maps for a certain area. Most of the data I find is from various places. One good source is this NOAA site: http://www.ngdc.noaa.gov/mgg/coastal/coastal.html
But this is pretty regional in resolution … I’d imagine for a fisherman you’d want very high-resolution images. That would take a lot more hunting around for the most appropriate. I will keep my eye open and post about it if I find something.
Is it not true that depressurizing the continental shelves through oil and gas extraction will accelerate coastal subsidence as landward strata slump into the evacuated pockets that held the oil and gas?
Google “North Sea floor subsidence” and you will note that the sea flor capping Norway’s Trol and Ekofisk oil fields has subsided a remarkable 25 feet!
Jim
Jim … that is a great question. I think you’re right that oil/gas production can influence subsidence. But, to what extent and how that differs case by case, I don’t know off the top of my head. I’d hate to speculate too much w/out looking into it some more. Something for a future blog post for sure. If any other readers know some good refs/links please put them here.
I notice that you discussed drilling for oil under salt formations. Just recently, a large sinkhole in Texas was blamed on the undermining and collapse of a salt dome.
Jim
Drilling in deeper and deeper water on the continental shelves means drilling closer and closer to the inflection point where the relatively gradual slope of the shelves plunges much more steeply to the oceanic abyss. In other words, the undisturbed strata that buttress the coastlines are getting thinner and thinner.
This can only lead to disaster. Should shelf subsidence cause the loose alluvial burden on the shelves to start to slide, what engineering marvel could prevent this moving silt from plunging into the abyss and generating a tsunami? Note that both sides of the Florida Strait, narrow and steep, are being actively considered for oil and gas extraction.
I(a layman) agree that each case is different, but subsidence in general due to mineral/fluid extraction is already so commonplace that alarm bells should be ringing loudly and clearly. Instead we get this fatuous “Drill, baby, drill!” political sloganeering, and the subsidence issue seems totally ignored in the rush to oil riches. Again, this can only lead to disaster.
Jim
Jim says: “Drilling in deeper and deeper water on the continental shelves means drilling closer and closer to the inflection point where the relatively gradual slope of the shelves plunges much more steeply to the oceanic abyss.”
There has been ‘deepwater’ (i.e., beyond the continental shelf edge) drilling activity in offshore regions of the Gulf of Mexico (GoM), Niger Delta, and Zaire/Congo canyon already (for the past 15 years give or take). There are certainly much fewer as compared to the shelf. And, at least in the GoM, there are numerous production platforms somewhat close to the continental shelf edge.
Jim says: “Should shelf subsidence cause the loose alluvial burden on the shelves to start to slide, what engineering marvel could prevent this moving silt from plunging into the abyss and generating a tsunami?”
So, do you mean that the entire shelfal area will ’tilt’ seaward causing sediment gravity flows? Are you envisioning a regional, larger-scale phenomenon or at smaller scales? I guess I’m having a bit of difficulty understanding what you are saying here.
In terms of generating a tsunami, the key ingredient is significant and rapid vertical displacement of the water column. The 2004 tsunami was caused by a thrust fault (subduction zone fault) that ruptured and vertically displaced the water column. Another potential hazard, which is more closely related to the process you are describing, would be a landslide event. Failure of volcanic edifices (e.g., Canary Islands) into the ocean can create this displacement of water. The effect of submarine landslides w/r/t tsunami generation is not very well known.
I’m not saying we shouldn’t be concerned, or even worried, about drilling-induced subsidence, but we need to carefully clarify exactly what the hazards are, where they are, how to mitigate them, and so on.
I see the problem of subsidence, whether gradual or sudden, as a fairly widespread phenomenon. The shape of our main Gulf oil field south of Louisiana, long(east-west)and thin, indicates that a fairly contiguous volume of the sea floor is essentially being hollowed out.
Lots of oil/gas sites are similar to the mouth of the Mississippi. The mouth of the Rhine is a major gas producer, the Niger as you said, the mouth of the Congo, the mouth of the Volga, the mouth of the Tigris-Euphrates, etc. All with loose semi-fluid alluvial deposits. Whatever the risk of subsidence-induced tsunamis, this situation is so commonplace the risk cannot be small.
Thanks for your helpfulness and courtesy
Jim
I don’t know of any particular examples of this kind of subsidence, do you? If the risk was more than minimal, surely there would be examples?
As discussed in Insurance Journal:
Subsidence — Some areas of the Gulf of Mexico floor have experience several feet of subsidence, or settling, related to production.
Usually, significant settling is found in older platforms because it can take 20 years to obtain 8 to 12 feet of subsidence. For example a platform installed in 250 feet of water 35 years ago may have been installed with a deck height of 45 feet. But after 20 years of production from multiple wells, there may be 10 feet of subsidence that reduces deck height to, say, 35 feet — leaving the platform more vulnerable to wave-in-deck loads never considered in the original design.
As discussed in Insurance Journal:
Subsidence — Some areas of the Gulf of Mexico floor have experience several feet of subsidence, or settling, related to production.
Usually, significant settling is found in older platforms because it can take 20 years to obtain 8 to 12 feet of subsidence. For example a platform installed in 250 feet of water 35 years ago may have been installed with a deck height of 45 feet. But after 20 years of production from multiple wells, there may be 10 feet of subsidence that reduces deck height to, say, 35 feet — leaving the platform more vulnerable to wave-in-deck loads never considered in the original design.
A further problem is that ground water, generally closer to the surface than deposits of oil and gas, migrates into the evacuated pockets that held the oil and gas. In essence, countries like Saudi Arabia are trading water availability for oil, not necessarily a good deal.
Jim
Jim … just an FYI (see today’s post), I’m disabling commenting for about a week while I travel. I’ve been getting a lot of spam lately … if you comment, it won’t be lost, but it won’t show up until I approve it next week.
DOI: 10.1306/5D25C0CB-16C1-11D7-8645000102C1865D
Progress of Exploration in North Sea
P. E. Kent (2)
AAPG Bulletin
Volume 51 (1967)
After an account of the occurrences of oil and gas in the countries adjoining the North Sea the paper outlines the regional structural features of northwestern Europe. The outcrop geology of the North Sea floor is described and followed by an account of the stratigraphic succession in the Tertiary, Cretaceous, Jurassic, Triassic, and Permian formations. Geophysical surveys have included gravity and magnetic surveys which define the main basins, and seismic work which has shown that salt structures ranging from non-piercing salt pillows to steep-sided diapirs are developed through most of the southern North Sea. Drilling has led to discovery of three gas fields of commercial size in the basal Permian sandstone up to the time of compilation of this paper. One additional dis overy since has been made in the…”
Note the commonalities of the various oil/gas regions.
Jim
The Storegga Slide: A Major Challenge on the Northeast Atlantic Margin
Espen Sletten Andersen1, Anders Solheim2, Petter Bryn1, Carl Fredrik Forsberg3, Kjell Berg4, and Tore Kvalstad3
1 Norsk Hydro ASA, Oslo, Norway
2 International Centre for Geohazards, Oslo, Norway
3 Norwegian Geotechnical Institute, Oslo, Norway
4 Pertra AS, Trondheim, Norway
The Ormen Lange gas field, which is the second largest gas field offshore Norway, was discovered in 1997. The field is located in water depths of 850 to 1100 m, in the central scar left after the Storegga Slide. This submarine slide occurred about 8200 years ago and is one of the greatest submarine slides ever recorded. Run-out is nearly 800km into the Norwegian Sea, and the volume of mobilized sediments is roughly 3000 km3. The affected area is 90 000km2, equivalent to nearly 30% of the Norwegian mainland, and the slide caused a devastating tsunami. The Storegga Slide is only the last in a series of huge slides in the same region during the last 0.5-1.0 My.
Extensive multidisciplinary geohazard studies have been carried out since the discovery of the field, including morphology, geophysics, regional and local geology, geotechnical borings, slope stability assessments, numerical modelling, gas hydrate studies, etc. The studies have revealed a close relationship between the variable glacial – interglacial depositional regimes and large-scale sliding. Long periods of contouritic, fine-grained deposition in an interglacial to interstadial regime, are interrupted by short periods of intense, rapid glacial deposition during peak glaciation. This caused excess pore pressure to build up in the buried deposits, reducing stability. The slide was triggered on the mid-lower slope and developed retrogressively.
The studies were performed in a fruitful cooperation between industry and academia, and showed that such an integrated, multidisciplinary approach was the key to success. Despite challenging morphological and geotechnical conditions, the Ormen Lange area is considered safe with regards to new large slides. The Norwegian Parliament approved development of the Ormen Lange gas field in 2004. This presentation emphasises on the slide morphology, the deposits and the geohazard aspects of the region.
I’m just a layman, but this kind of thing doesn’t seem very safe to me, and it’s going on all over the world.
Jim
The Ormen Lange gas field is described as centered under the massive Storegga slide, described as one of the greatest submarine landslides ever.
Note that North Texas has been experiencing what was described as “unusual” seismic activity in the last couple of months. This seems to include the Barnett shale formation, where large-scale gas extraction has just begun.
Too many common factors among mineral extraction, subsidence and seismic activity to be realisticly written off as coincidence.
Point made?
Jim
Jim … are you claiming that Storegga slide was triggered by drilling activities?
No. I’m suggesting that the centrality of the large gas field to the slide area implies the possibility that the slide was caused by a major “burp” of the gas field , which then destabilized the alluvial deposits and caused them to move suddenly.
As I say, I’m just a layman; would such a “burp” necessarily leave specific evidence of its occurrance?
Jim
I see … well, if gas was leaking to the surface (either slowly or catastrophically) at some point in the past (at least as old as 8,200 yrs per age of slide) then there probably wouldn’t be a gas field left at all. That is, the trap and seal would’ve been compromised. But, I don’t know anything about the details of that area or those fields, so I can’t say for sure.
In terms of evidence for an ancient “burp” … that’s tough because the effects it has on what can get preserved (i.e., the sediments) is secondary and thus subjective.
But, again, I’m no expert on slope stability issues. Some quick googling found a couple docs that might interest you or at least lead you down a path to finding relevant references:
Slope Stability and Land Slides in the Deep Sea:
Influence Parameter Gas Hydrates
http://www.bgs.ac.uk/oml/docs/downloads/9/58/GrupeKiel2002.pdf
A simple model for submarine slope stability analysis
with gas hydrates
http://www.geologi.no/data/f/0/09/15/4_22301_0/60713_NGT_no_3_06_17.pdf
These are both specific to gas hydrates but have information regarding the parameters considered by geoengineers when evaluating/mitigating slope stability in areas where gas could be a hazard.
The first reference you provided begins with the following comment:
“Decomposition of gas hydrates is thought to be a major cause for the instability of submarine slopes and deep sea floor….”
Apparently this concept has been knocked aroound since at least 1982.
Long-term oil seeps are of course commonplace in places like southern California and offshore G-O-M. Mexico’s supergiant offshore field, Cantarell, was discovered when a fisherman kept complaining to authorities about oil (which turned out to be from seeps) fouling his nets and the Mexican government finally investigated. In the novel “Oil”, about southern Cal’s oil industry, Bunny and his father hit the mother load when they notice an oil seep and decide to take a chance. Even in this instance, the author noted a coincidence between oil deposits and earthquakes.
Jim
Jim says: “Even in this instance, the author noted a coincidence between oil deposits and earthquakes.”
I’m not sure what you mean here … that the occurrence of petroleum is near faults? Or that the timing of earthquakes is related to the extraction? There is plenty of data to investigate this relationship.
Jim, I’m happy to keep discussing this but, to be honest, I’m a bit unclear of what you are trying to say. I apologize if I don’t understand. I need you to refer to more specifics, more hard data.
Where I’m going ultimately with all this(which I’ve been doing since 1978)is to argue that offshore oil extraction should be phased out because of the threat of catastrophic subsidence, in favor of the shale oil deposits of Utah, Wyoming, and Colorado.
The smallest estimate of the amount of shale oil in the deposits is 400 billion barrels. With our present oil consumption at 22 million barrels per day, 400 billion barrels theoretically provides 25 million bpd for forty years, enough to provide a bridge fuel to a presumably more technically advanced future, and incidentally to crush OPEC.
Given that this so completely dwarfs the several tens of billions of barrels potential of offshore extraction, offshore drilling might as well be phased out, the subsidence threat avoided, and investment capital put to other uses.
Oil shale has important advantages. The deposits are within a 2000-mile radius of Des Moines, Omaha, St. Lois and Chicago to the East, and Las Vegas, Phoenix, and Southern Cal to the West. Because the shale lies athwart the Continental Divide, the shale is uphill from most of its markets.
The oil would require some pumping , but when you’re moving millions of tons of product, the ability to do it mostly with, rather than against the force of gravity, is significant.
There are certainly coincidences between oil deposits and faults and actual seismic activity. Canterell is situated in a web of great cracks in the Earth’s crust left by the asteroid that hit Yucatan 60 million years ago. Tangshan, site of a devastating quake in 1976, is on the rim of what was China’s largest active offshore field.
Significant oil fields in Sumatra are in proximity to the fault that caused the great Indian Ocean tsunami. Baluchistan, newly productive of natural gas, suffered a major quake, while the adjacent Iranian hinterland north of the Persian Gulf, has suffered many quakes as well. Sakhalin is another example of this dualistic phenomenon, and of course Southern Cal.
The public(speaking as a layman) understands tectonics in generalities; that is, a great continental plate butts against another great continental plate. In reality, where the plates meet are continental “crumbs”, bits of crust that are minimal in geological terms, but vast multi-county areas in human terms. All these “crumbs” are pressed together like the stones in an arch and hold each other in place.
Oil extraction is now getting well below 20,000 feet, and some of this is near faults. This is getting to be at the depth from which shallow earthquakes spring. It is easy to imagine extraction and consequent slumping activating a fault and causing one of the crumbs to shift, activating the other crumbs in response.
Makes sense to me.
Jim
Jim, while it may make sense … our understanding needs to be founded in data. I’m not saying the data doesn’t exist, I haven’t explored this topic … perhaps you can list some specific books/articles that discuss these topics?
An example of this subsidence/slumping effect is the new fault that appeared accross the “neck” of the Mississippi Delta south of New Orleans and northward of the Delta’s southernmost point.
This is consistent with what I have been saying. While the fault is now opening very slowly, there is no telling if the spreading will accelerate, and if extraction becomes widespread in even deeper water, spread acceleration would be expected.
Note that this slumping effect need not become apparent very quickly. The new Mississippi Delta fault only appeared after decades of offshore extraction–thousands of square miles south of the delta being undermined, and many more to come.
Jim
Just thought I’d throw this in, recognizing the need to demonstrate an alternative to offshore oil.
Neither party seem to get it economically. We are facing an annual shortfall of a trillion or a trillion-and-a-half dollars in investment capital to meet the renovation needs of our infrastructure, our manufacturing sector, our armed forces, and our health and education systems. This is about ten percent of our present GDP, and can only be accomplished in a low-tax, pro-growth environment.
How? Specifically, do first that which can reach fruition first. Concentrate on that which has the most beneficial secondary effects. Concentrate on that which can achieve a broad national concensus. A few examples:
1. A program of national housing renovations would put tens of thousands of tradespeople back to work, put a prop under sliding real estate values, and would begin to save energy from the moment the first broken window were fixed.
2. The “gross-effect battery” uses bulk waste products, such as acidic mine seepage, manure holding ponds, windrows of spoiled fruit, and garbage leachate as bulk electrolytes in crude but very large batteries. These bulk waste products are commonplace in society, and their electrochemical potential might as well be used as the waste would exist anyway, while the gross-effect battery can be designed to produce fresh water as a by-product.
3. Piezoelectric cells generate electricity when the cells suffer mechanical distortion. Many natural processes generate vast quantities of mechanical energy which is now wasted but available to be tapped: earthquakes, volcanoes, geysers, windstorms, avalanches, and many other examples abound. The calving of icebergs from glaciers involves the movement of million of tons of frozen fresh water, which movement could be translated into electricity while the water could be preserved from salt contamination.
4. Abrogate housing codes that demand high-maintenance landscaping and do not allow clothes to be dried on outdoor lines. “No blood for oil!” makes for a snappy slogan, but it does not answer the question of where the fuel for our economy will come from.
5. The smallest estimate of oil in Rocky Mountain shale is 400 billion barrels. This is enough to provide 25 million barrels per day for the next 40 years and to crush OPEC(our present oil consumption is 22 million BPD).
6. Incorporate regenerative shock absorbers into cars, along with regenerative brakes.
7. Develop urban agriculture, and incorporate community gardening into school curricula.
This would take millions of truck ton-miles off our overstressed highways and reduce pollution and wasteful congestion.
8. Emphasize the exploitation of “inner space”–the sea floor and upper atmosphere–over “outer space”. This would vastly accelerate returns on investment(I have a patent regarding bathysphere exploration).
I have no wish to understate the problems facing our country, but clearly there is no reason we cannot overcome them. “Do first that which can reach fruition first.”
Jim says: “An example of this subsidence/slumping effect is the new fault that appeared accross the “neck” of the Mississippi Delta…”
Is this your observation? I need a reference … where’s the data?
ect
Subsidence and Fault Activation Related to Fluid Energy Production, Gulf Coast Basin Project
Subsidence Related to Fluid Energy Production Home
Introduction:
Project Overview
Investigators
Research Objectives:
Production Parameters
Reservoir Parameters
Framework
Ground Characterization
Geophysical Methods
Land Loss
Publications
Project Contact:
Bob Morton
Related Link:
» USGS Energy Resource Program
Introduction
Image showing possible effects of petroleum production.
Figure 1. Possible effects of petroleum production. Prolonged or rapid production of oil, gas, and formation water (2) causes subsurface formation pressures to decline (3). The lowered pressures (3) increase the effective stress of the overburden (4), which causes compaction of the reservoir rocks and may cause formerly active faults (1) to be reactivated (5). Either compaction of the strata or downward displacement along faults can cause land-surface subsidence (6). Where subsidence and fault reactivation occur in wetland areas, the wetlands typically are submerged and changed to open water (7). Figure is not to scale. D, down; U, up.
The Gulf Coast Basin is a region where subsidence and fault activation are common around large, mature oil and gas fields even though moderately deep hydrocarbon production has generally been disregarded as the primary cause.
This project will test the hypothesis that long-term, large-volume oil and gas production in the Gulf Coast Basin has resulted in land-surface subsidence and activation of deep-seated faults around some fields. The project will:
* Investigate the magnitudes of environmental impacts;
* Estimate rates of deformation;
* Identify reservoir parameters that are indicators of subsidence potential; and
* Evaluate geophysical methods for regional subsidence detection and monitoring.
Other tasks will be to:
* Investigate the mechanisms and timing of subsidence;
* Determine if the processes are still active;
* Examine the environmental changes such as reductions in land elevations and elimination or replacement of plant communities;
* Develop conceptual and empirical models to predict subsidence impacts on the basis of production histories and regional geologic framework.
The results of these investigations will provide a basis for designing marsh and barrier-island restoration projects, planning hurricane levees, and managing oil and gas production.
thanks … looks like this link, right?
http://coastal.er.usgs.gov/gc-subsidence/
$2,835,823
Our Goal: $6 million
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Michoud fault
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The Michoud fault is a geological fault line that runs through eastern New Orleans. [1] The Michoud fault is the subject of extensive scientific inquiry into why Louisiana is losing vast tracts of land. [2]
Subsurface mapping identified the Michoud fault, on the basis of well cutoffs and seismic surveys. [3] Sedimentary growth implies that movement along the Michoud fault has been intermittent since Oligocene time (Bebout and Gutierrez, 1983). A cross section in McBride (1998) shows a high-angle normal fault that was correlated by Dokka (2006) with the Michoud fault. This fault merges with a low-angle detachment fault at –7 km deep that developed along the top of a slightly south-dipping zone of weak salt and shale. These structures are considered to be related to a regional south-vergent extensional-contractional complex described by Peel et al. (1995; Fig. 1). Movement of the complex and thus on the Michaud fault reflects gravitational instabilities and down-dip motion during times of high sedimentation (Peel et al., 1995).
The Michoud fault belongs to a class of geologic structures known as growth faults (Mauduit, T., Brun, J. P. 1998). Growth faults are common geologic structures of regions undergoing high sedimentation rates, such as river deltas and passive margins. They often develop where weak rock layers (detachments) such as salt, anhydrite, or shale underlie regions of rapid sedimentation. These weak zones allow the growing mass of material above them to slide downhill, either continuously or episodically. These downslope movements will be correspondingly experienced in the headwall region (such as that occupied by the Michoud fault) either as slow (barely perceptible) or rapid (catastrophic) subsidence. Growth faults are also sometimes called “listric faults”, implying that the fault is a concave-upward surface that transforms nearly vertical displacements at the surface into nearly horizontal ones at depth.
The Michaud fault is not unexpected or unusual as a geologic feature of the Mississippi Delta. Holocene faulting and tilting is widely recognized in many world deltas, such as the Nile, the Ganges-Brahmaputra, the Yangtze, the Po River, and the Rhine.[4]
[edit] References
* Bebout, D.G., and Gutiérrez, D.R., 1983, Regional cross sections, Louisiana Gulf Coast: Baton Rouge, Louisiana Geological Survey Folio Series 6, 10 p.
* Dokka R.K., 2006. Modern-day tectonic subsidence in coastal Louisiana. Geology vol. 34, p. 281-284.[1]
* Hickey, M., and Sabate, R., eds.,1972, Tectonic map of Gulf coast region, U.S.A.: Tulsa, Oklahoma, Gulf Coast Association of Geological Societies and American Association of Petroleum Geologists, Scale 1:1,000,000
* Peel, F.J., Travis, C.J., and Hossack, J.R., 1995, Genetic structural provinces and salt tectonics of the Cenozoic offshore U.S. Gulf of Mexico: A preliminary analysis, in Jackson, M.P.A., et al., eds., Salt tectonics: A global perspective: American Association of Petroleum Geologists Memoir 65, p. 153–175.
* Törnqvist, T.E., Bick, S.J., van der Borg, K., and de Jong, A.F.M., 2006. How stable is the Mississippi Delta? Geology vol. 34, p. 697-700.[2]
* Mauduit, T., Brun, J. P. 1998. Growth fault/rollover systems: Birth, growth, and decay. J. Geophys. Res. Vol. 103 , No. B8 , p. 18,119-18,136.
[edit] References
1. ^ Geologic Faults Cause Structures In New Orleans to Sink, Study Says
2. ^ http://www.cbsnews.com/stories/2006/03/31/tech/main1459939.shtml
3. ^ (Hickey and Sabate, 1972)
4. ^ (Törnqvist et al., 2006)
[edit] External links
* Fault Motion Animation
* Tectonic control of subsidence and southward displacement of southeast Louisiana with respect to stable North America
* Baton Rouge – Denham Springs Fault System, Lake Pontchartrain
Retrieved from “http://en.wikipedia.org/wiki/Michoud_fault”
Categories: Structural geology | Geographic areas of seismological interest | Seismic faults
Jim, you don’t need to copy/paste in everything from a page … just the link (if available) or the full citation of a paper (authors, year, title, journal/book/website, etc.) is fine.
I’ve been posting fuller accounts because it makes it more convenient for the discussion, as well as for interested 3rd parties who may pop in from time to time, to have the relevant material right on the thread, rather than having to re-access info every time. Does this impinge too much on your computer’s memory?
Thanks again for your patience and a most informative(from my point of view)blog.
Jim
Ref. FORBES, 11/24/08, p 73
This article discusses Shell’s Perdido field in the G-O-M, some 200 miles offshore and in water at least 7,500 feet deep.
This is at least 50 miles beyond the present major oil extraction zone, which runs in a narrow east-west crescent south of the Miss. Delta, and(according to the article) at least 4,000 feet deeper than what was considered “deep” water just a few years ago.
In other words, there is a strong gravitational gradient between the present main production zones and the proposed new zone. Likewise, the article describes the Perdido field as being situated accross “multiple fault lines”–in other words, the “continental crumbs” I have posited. Extraction and resultant pressure diminuation seem very unwise.
Perdido is exhibit A in my Pantheon of Ghastly Conclusions, but it is hardly the only one. The above recent posts specificly cite the Nile Delta as suffering the same kind of stress faulting as the area from New Orleans southward, and likewise having gas deposits in its hinterlands(offshore Gaza and elsewhere). There can only be a similar result–subsidence, and salinization of delta farms, a catastrophe for Egypt–while the continental shelf offshore Gaza is narrow and steep, an invitation to catastrophic subsidence, especially as the hinterland of Gaza includes the active Arava Fault on which the Dead Sea(many new sinkholes)lies.
As I said, there are so many similarities–oil and gas deposits offshore of highly-sedimenting rivers, large fields discovered near areas subject to stress faulting The whole Gulf of Mexico coastline from Cuba around to Florida, Alabama, Louisiana, Texas, Mexico, Maracaibo, and eastward offshore and to the Orinoco Delta–an enormous connected crescent hundreds of miles long crossing numerous faults. It is impossible not to conclude that the great oil bonanza and the subsidence it induces will end with a tremendous thud somewhere.
Jim
New York Times, Dec. 2,, 2008, page D 3
An article in today’s Science Times regarding iceberg formation provides an analogy to the seaward creep of land masses and acceleration due to submarine subsidence:
“…Scientists studying the potential impact of climate change need to be able to simulate how ice sheets and shelves behave, including how fast icebergs form. But no one has been able to formulate a basic rule for calving.
“Now Richard B. Alley of Pennsylvania State University and colleagues have come up with one. The rate of calving, they report in Science, is primarily a function of the rate at which an ice shelf spreads.
“This rather simple rule was devised after long study of data from ice shelves, including the largest in the world, the Ross Ice Shelf in Antarctica. They found that faster-spreading shelves have a higher rate of calving, while shelves that spread more slowly DUE TO BUTTRESSING FROM THE SIDES OR THE SEA FLOOR(my emphasis)produce icebergs at a lower rate…”
Disregard the fact that the ice fragments will float and the strata fragments will sink due to their greater density. It is clear that ice creep, and by implication the seaward creep of strata, is moderated by the buttressing effect of the regional continental shelf. Given that sea floor subsidence due to oil extraction(which we agree is commonplace)can only diminish this buttressing effect, it seems reasonable to conclude that offshore extraction can only accelerate this creep, whether we are talking ice or somewhat plastic strata. This is especially true where an enormous alluvial weight is deposited annually, enough to cause stress fractures, as at the mouths of major river systems like the Mississippi.
That seals it.
Jim
Brian–I would like to talk about my bathysphere patent, because I would love to get some feedback from the professionals here, some of whom are active in undersea exploration. As I have a commercial interest in it, I thought it best to get your permission first.
Jim
Jim … I’m a bit confused why you need any permission from me for anything. I’m just a guy with a blog. Feel free to elaborate here or you can e-mail (see the ‘About’ page) if you want.
Brian–many site managers object to members discussing their commercial interests, for fear of people getting conned.
At any rate, this is a summary of my patent, #6,438,957, “Piezoelectric Power Generating Arrangement Activated By Elements Caused To Rotate By Natural Energy Source”. I am a great believer in the future of undersea exploration; the patent describes what is essentially a cargo bathysphere functioning as a funicular car between a floating base on the ocean’s surface and bases at various depths and especially the bottom. The mechanical energy of the bathysphere’s descent and ascent is converted into electrical energy and compressed hydrogen and oxygen which are delivered to the undersea colonies along with the standard cargo.
The bathysphere empty is positively buoyant, it will float unloaded. As desired, the compressed hydrogen and oxygen could be used to affect the buoyancy.
The bathysphere has lateral hatches to facilitate loading/unloading. It also has a vertical hatch at the top for the initial loading at the surface. The bathysphere is intended to moor under a floating supply base or between the hulls of a catamaran supply ship. Initially, the, top hatch of the bathysphere is flush with the deck of the supply base or catamaran.
The bathysphere is held in place by piezoelectric latches. Thus, as the craft is loaded, the weight of the cargo will increasingly stress the latches and cause them to emit an electrical charge, which in turn could be stored in batteries or as pressurized hydrogen and oxygen electrolyzed from the ambient sea water.
When the bathysphere is released to begin its descent, the latches are immediately de-stressed, again causing the piezoelectric cells to emit a charge comparable to the entire weight of the craft and cargo, which charge can be further stored or utilized. The craft is piezoelectric-coupled to a cable between the floating base and the subsurface base; thus it rides the cable down.
The hull of the bathysphere is mounted with diaphragm-like tubes. The flexible head of the diaphragm is connected internally to a toothed rack which meshes with a gear on a shaft.
As the craft descends, increasing water water pressure forces the flexible head of the diaphragm inward and thus drives the toothed rack against the gear, thus turning the shaft and producing either AC or DC electricity as desired. The descent may be stopped at any desired depth, causing the piezoelectric coupling to emit an electrical charge proportional to 1/2mass X velocity squared, both at stop and restart.
At the bottom, the bathysphere is engaged by piezoelectric latches, again producing electricity proportional to 1/2 massX velocity squared, which in a descent of miles could be very large.
As the craft is unloaded, it becomes increasingly buoyant, again stressing the piezoelectric latches. The craft is then re-loaded for the trip to the surface, allowing for the innate buoyancy to lift the craft back. It seems likely the trip down will carry heavy equipment for expanding the undersea colony while the trip up will carry small, high-value objects suchh as geological and biological samples and refined gold or gems.
As the bathysphere rose, the decreasing water pressure would draw out the head of the diaphragm, causing the toothed rack to again turn the shaft, but in the other direction, producing AC/DC.Thus a highly profitable long term energy exchange , producing surplus electricity and pressurized gases in both descent and ascent, would be established.
Comments?
Jim
Jim … sounds interesting … but, I have absolutely zero technical expertise in this and really can’t offer anything of value. Sorry. You might see what the guys at the blog Deep Sea News think (http://blogs.discovery.com/deep_sea_news/) — they have way more knowledge about deep-sea equipment and exploration than I do. Good luck with your endeavor.