Sunday, 22 November 2009

Interview with Dr. Randy Marrett

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If you regularly read this blog (I guess that is something boring, because I don't regularly upgrade it...), you have noticed that I have changed, once again, the layout of the page. Well, this time is quite a definitive change, I like it now, finally. It is clear and neat. Please, allow me a few days to make all work properly!.

I have thought that it would be interesting to put in the right side bar some videos from time to time related with structural geology. I will start this series of videos with an interview with Dr. Randy Merrett, associate professor in the Department of Geological Sciences at the University of Texas.

As the introduction of the video states:


Dr. Marrett's research concentrates on deformation processes in the upper continental crust where folds, faults, and opening-mode fractures are the most important products. This work is applicable to a wide range of human concerns such as natural hazards (e.g., earthquakes, volcanoes) and the flow of fluids through rock (e.g., hydrocarbons, water, contaminants). Some common themes that relate his disparate interests are quantitative field observations and analysis, especially using techniques that address spatial and size scaling of structures. Dr. Marrett currently has on-going projects that address active faulting and geyser eruption patterns in the Central Andes of Argentina and Chile, detachment folding and curved orogenic belt development in the Sierra Madre Oriental of Mexico, and opening-mode fracturing in numerous areas.




Quite basic, but always useful for forwarding it to people who want to know more about what we do.

Enjoy it!

Saturday, 21 November 2009

Geo-Logic Systems, bought by Halliburton

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Halliburton has recently acquired Geo-Logic Systems, the producers of Lithotect, the balancing and restoring software. It has been announced in several E∓P websites, and also in the corporative websites of both companies:

On Tuesday, October 27, Halliburton announced its acquisition of Geo-Logic Systems, LLC. “The industry faces increasingly difficult exploration and drilling scenarios,” said Paul Koeller,Hal liburton’s vice president of Software and Asset Solutions. “The integration of Geo-LogicSystems offers ge oscientists advanced modeling solutions to address the technical challenges of exploring in complex petroleum regimes such as overthrust belts and the pre-, syn- (including sub-salt) and post-ri ft portions of extensional basins. In these complicated, poorly imaged plays risk reduction is of paramount importance.”

That is probably a big step for Lithotect, a great piece of software. Now, being part of such a huge company like Halliburton, surely the rivarly with MVE's Move (formerly know by its different components: 2DMove and 3DMove) will tight up, and this will be clearly in benefit of the customers.

Halliburton owns already the giant of seismic software, Landmark, and this acquisition points out to the direction that E&P is taking in the last years: Structurally complex scenarios, fold and thrust belts, deep water belts, sub-salt environments, etc, which need serious expertise on structural geology and risk reduction. Well, let's revisit our notes and books because there is a lot of hard work waiting for us...

Monday, 2 November 2009

Recording planes with strike or dip? The problem of the right-hand rules

20 comments
When we want to record the orientation in space of a geological surface (e.g. a stratigraphic body), we have two different ways of doing it:
a) Dip direction and dip angle: Dip direction is just the direction toward which the plane is inclined. Dip angle is the angle of inclination of the plane. In the example included in this article, we would write it down as 090/45; the plane is inclined 45º towards the east (090º). Easy.
b) Strike and dip angle: Strike is the direction of the imaginary line which would represent the intersection between the plane and a horizontal surface. But here it comes the problem: the strike, as we know, can be represented by two different conjugated angles, and we need to follow some kind of convention; typically, the strike is expressed as the acute angle between the intersection line and the north direction. In our example, it would be 0ºN. But how which convention we take for indicating towards which direction is dipping the bed? For that we use the right hand rule.

There are two different right hand rules... Did you know that? Oh, that is not very convenient...
  • American right hand rule: Looking to the strike direction, the bed dips to the right. In our example, that would fit with 000/45. So, looking to the north, the bed dips to the right, to 090 (east).
  • British right hand rule: The thumb of the right hand indicates the dip direction, and the heal points to the strike direction. So in our example, we would record the orientation as 180/45. That is: Strike towards 180 (perfect south bearing), and dip of 45º towards 090.
Usually, if the person who took the measurements knew that other people MAY HAVE different criteria expressing the same results, the data can be recorded as

180/45E

Which would mean, no doubt, a strike of 180 and a dip direction towards the east, with a magnitude (dip angle) of 45. If you use strike, please remember to write always as a companion of the dip angle the quadrant where the dip direction would be. For example, 045/56SE. In this case we are talking of 135/56 (dip direction/dip angle). 045/56NW; now we would be talking of 315/56 (dip direction/dip angle).

But what happens with measures like:

45W/34

What does that mean? I have seen it. Does it mean 45º from north towards west, so 315? or does it mean strike of 045 and an a dip angle of 34 towards W? Is that? Uh, I don't think so.

The truth is that, besides right-hand rules, many geologists use other conventions, sometimes personal ones, and maybe in a wrong way. Perhaps using only NW and NE quadrants for the strike. Perhaps not.

It is clear that using strike values when representing the orientation of a bed we are introducing a risk factor if we don't state clearly which right hand rule we are using. Of course, for some people in some situation the usage of strike/dip angle may be very useful:
  • When we speak of general trends in a big area (e.g. an orogen, in order to show that a trend is parallel or not to the structure).
  • In a mine, in order to visualise quickly if the strike direction is the same as certain mineralisation or lineaments.
  • In engineering geology, for the same reason, in order to know if the bedding/joints have the same orientation than a well, a tunnel, etc.
I would suggest another right hand rule... If you use strike for describing the attitude of a plane, your right hand should be cut!.
But perhaps that is very extreme... so far.

Friday, 2 October 2009

Structural Geology @ Facebook

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I am totally absorted with my renewal work in another website (about Poland, if you are interested, although it is in Spanish), and I am planing to write up some articles for this blog about basic structural geology. Perhaps I should say "not so basic stuff but something we should have always in mind".

And something I have realised now is that I totally forgot to post here the creation, some months ago, of a "Structural geology and tectonics" group in Facebook. Raik and I are the administrators of the group.

If you are an user of this social network (you are in another planet, or perhaps you are still resisting to join it... now is the moment to do it!), you are invited, encouraged, to join us there. I wonder how I can do a more direct link between this blog and the group, but first things first: writing about geology!



Friday, 17 July 2009

DRT 2009 conference in Liverpool

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As it has been communicated in the Geo-Tectonics mailing list, the “Deformation, rheology and tectonics” conference in Liverpool will take place this September, between the 7th and the 9th.

In their own words, “In 2009, DRT is a joint venture between the universities of Liverpool and Manchester, and is to be held in the contemporary cityscape of the rejuvenated Liverpool Docklands.

As many of you are aware, 2008 was shrouded by the untimely loss of Dr. Martin Casey.  This meeting is dedicated to Martin, and events and sessions will be organised in his memory.

The conference includes two fieldtrips: A pre-conference trip to the Mam Tor Landslide (Derbysire, England) on the 6th of September 2009 and a post-conference trip to the Isle of Anglesey (north Wales) from the 9th to the 11th of September of 2009.  (http://www.liverpool.ac.uk/PDMearth_sciences/dept/drt2009/fieldtrips.html)


The site is www.liverpool.ac.uk/earth/drt2009, and you can see the programme in here: www.liverpool.ac.uk/earth/drt2009/programme.


Monday, 13 July 2009

M6.3 earthquake in Taiwan

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If you have been listening to the news in the last hours, you probably know already that a M6.3 earthquake has struck offshore Taiwan. As usual, the best information comes from the USGS.

The event happend at 18.05 UTC, and we don't yet have a focal mechanism solution for it. Anyway, in the attached figure you can have an idea of what is going on in there.

Taiwan is located in the boundary between the Phillipine Sea and the Eurasian plates. There is an approximated convergence rate of 80 mm/yr to the SE. What is really especial about this island is the presence of two subduction zones: One, where the South China Sea subducts beneath Eurasia, and another one, where Eurasia subducts beneath the South China Sea, forming both zones approximately a right angle.

You can see a great introduction (including the previous explanation) to the geology of Taiwan in the dedicated website of the
California Institute of Technology:

http://www.tectonics.caltech.edu/taiwan/regional.htm



Sources:

- http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009jabu.php
- http://www.tectonics.caltech.edu/taiwan/regional.htm

Sunday, 12 July 2009

Comments available again!

1 comments
In the last days I have been trying to fix the problem we had with the comments, which now they work again!

The problem was fairly simple: although we have our own domain, the blog is enginereed by www.blogger.com, and it seems they don't fit as nicely as we expected.

Probably, if you have been visiting this website in the few days, you have been we have been trying some fancy designs... I promise the final one will have a geological look, just give me a couple of days!!

So... post your comments, they are more than welcome!

Wednesday, 1 July 2009

Download ASTER GDEM

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On Monday 29th of June of 2009, NASA and Japan’s Ministry of Economy, Trade and Industry, released the Global Digital Elevation Model (GDEM) created from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data. That has involved the processing of more than a million ASTER scenes, in order to cover Earth’s land surface between 83 degrees North and 83 degrees South.

The result is a 30-m resolution digital elevation model available from the following URL: ASTER GDEM . In this website the GDEM can be downloaded selecting by tiles, by polygon, by shapefile and of course, by coordinates.

So far the standard DEM was the SRTM data, obtained during a flight of the Space Shuttle in 2000. Its resolution is approximately 90 m (30 for USA), and has proven to be a very valuable resource in structural geology, hydrocarbon exploration, geohazard analyses, etc. GDEM will predictably become a new standard, with a commercial resolution and global availability.


363788main_pia12090-516.jpg


Important links:

Tuesday, 23 June 2009

Problems with the comments

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I apologise for the error in the web that doesn’t let you to leave comments in the articles. I will try to fix that in the next days. Apparently it is just a small bug in the template I am using, nothing else! I’ll keep you updated about that.

Thanks for reading this humble place :)

Jorge

Monday, 22 June 2009

Move and LithoTect for free

6 comments
Dr. Alan Gibbs, director of Midland Valley Exploration, has announced in the Geo-Tectonics list that their software Move2009 (which includes 2DMove, 3DMove and 4DMove) is now available for free to universities for teaching and research.

He recommends contacting MVE through their website or using this email: help@mve.com

Move2009, as described by MVE, is “fundamentally different from other geo-modelling and model building software as it incorporates geological time into the modelling process. Other modelling tools simply create good-looking models from the present day interpretations, ours turn the modelling process into a rigorous analytical activity involving geological time, with interoperability support of modelling environments and the ability to easily transfer files between all Move components. Using our products geoscientists can continually challenge and test their assumptions and thereby gain a far deeper understanding into the structural geology they are modelling”.

Is that the only geo-modelling software available for building and balancing cross sections and general structural modelling? No. In the same list, Dr. Robert Ratliff, development director of Geo-Logic Systems, reminds that their software LithoTect is also available for free for universities (as it has been for many years). This software combines the power of geological modelling with a very attractive conditions in terms of available platforms and licensing conditions.

Well, the choice is in your hands. Perhaps you want to make a comment comparing both suites?


Friday, 19 June 2009

Earthquakes in Google Earth

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A good habit I have acquired during the last months is to take a look to the recent seismic activity of a region before starting to work in there, in order to get a quick idea of what is going on. This habit can be more illustrating that it initially seems.

USGS provides a KMZ file with a very friendly and attractive interface for Google Earth. It loads the major earthquakes in our planet for the last 7 days, classified by time (Last hour, Last day, Last week), and by magnitude (from 1 to 8). If you click on each individual earthquake, you will open a box with its basic information and the url link for opening in your browser the complete information about it.

You can load this file in your Google Earth from the dedicated USGS website for seismology:

http://earthquake.usgs.gov/

It is on the left, "Google Earth KML". Anyway, the direct link to the file is:

http://earthquake.usgs.gov/eqcenter/catalogs/eqs7day-age.kmz

The interface also loads plate boundaries and convergence rates, measured in mm/year. I haven't found the source of the rates, but let's accept that if the data comes from USGS, should be fine. The plate boundaries included in the KMZ file are:

- Subduction zone.
- Oceanic transform fault.
- Oceanic spreading rift.
- Oceanic convergent boundary.
- Continental transform fault.
- Continental rift boundary.
- Continental convergent boundary.

Of course, don't expect a very precise location for the plate boundaries! It is just an indication of the global tectonics of each area, in order to put the earthquakes in a correct geodynamic context.

Personally I find this KML file very useful, not only for the very up-to-the-date information given, but also for the boundaries, the rates... Useful thing when we have to prepare a simple figure in Corel or Freehand for a report.

Again, the links:

http://earthquake.usgs.gov/
http://earthquake.usgs.gov/eqcenter/catalogs/eqs7day-age.kmz

There are more KML's and KMZ's providing similar information, but that will be for another day.

Enjoy!

Wednesday, 27 May 2009

Graphical templates for Structural Geology

1 comments
We all need from time to time to print a stereographic projection net, a Kalsbeek counting net or a rose diagram. Courtesy of Holcombe, Coughlin & Associates (http://www.holcombecoughlin.com) today we bring you a document (pdf format) with several graphical templates for structural geology (and mineralogy too!):
The content of the document includes the following diagrams:
Stereographic projection nets (several sizes, 20 cm, 15 cm, 10 cm and 5 cm):
- Lambert equal area projection (Schmidt net).
- Polar equal area projection.
- Equal angle projection (Wulff net).
Rose diagram net
Kaalsbeek counting net
A simple but very useful document, as we can have in a single pdf all the basic diagrams we can need in the field. Now print it and start to plot data!

Wednesday, 15 April 2009

Obituary of Prof. Maurice Mattauer

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I have read today in the Geo-Tectonics distribution list the obituary of Prof. Maurice Mattauer, who passed away on the 8th of April of 2009. I copy it here, and please accept my apologises for the late posting, but I just read that this morning:
Homage to Professor Maurice Mattauer *
** Holding the latest scientific advice that he wanted to give on the earthquake of Aquila in Italy, to appear in the "Gazette de Montpellier", 9 April of this year, Professor Maurice Mattauer died accidentally at his home April 8 2009.
Born in 1928 in Sentheim (Alsace), he makes his higher education in Besançon, he joined the CNRS in 1951, to conduct a thesis in Ouarsenis Algérien, then it will work for the service of the Card. He returned to France, appointed Professor at the University of Montpellier in 1959 where he became the leader of the team of Structural Geology. It will remain at his post as leader of Geology montpelliéraine until 1996, then Professor Emeritus of the University of Montpellier 2 until 2003. It will continue until the last few days, to come to the meeting of young researchers and former students to give its advice and criticism.
Motivated and dynamic teacher, he brought his passion for geology, rocks and fossils, to generations of students, who followed his footsteps and then raised his voice and his methods in other universities.
His books and numerous publications in the direction of specialists in the discipline "Tectonics" or the general public to share his love of the mountains and rocks all have a huge national and international success.
The mountains were his passion, and has published numerous works in "écumant " first outcrops around Montpellier, discovering in himself, with his legendary flair, fossils largest in the region such as dinosaur eggs from the Upper Cretaceous. It will launch here the foundations of the modern tectonic mapping is special for students awarded by Montpellier. It shows the importance of observing the microstructures in the understanding of mountain ranges.
After the Pyrenees, the Alps and the Massif Central where he will propose the first coherent tectonic models, he embarked on the visit of the mountains of South America and Asia, in cooperation with the Andean countries and China. He will also visit the Mountains of North America, but also the Mediterranean for which he published in 2008, the last scientific article, full of new ideas and always served by the quality of its graphics innate.
All persons who have approached Maurice Mattauer and all students have recognized him quickly an outstanding scientist and passionate living for his Science.
It forms part of this, these few men, leading others by communicating their passion to advance or to excel. It was, ultimately, a chance to have met!
During his career Maurice Mattauer has received numerous awards and honors, especially the prices of Geological Societies of France and Belgium and the Academy of Sciences.
He was also promoted to the rank of Officer of the Legion of Honor.
Pr. Maurice Brunel, Montpellier
* His funeral have been held in Grammont-Montpellier on Tuesday 14 April *

Monday, 6 April 2009

Mw 6.3 Earthquake in Italy

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We got up this morning with the terrible news from Italy, where last night an earthquake affected significantly the location of L’Aquila in the Central Apennines region resulting in more than 90 killed (so far, at 14.00 GMT, and surely the number will increase in the next hours).

The Apennines are an accretionary wedge formed as consequence of the subduction of the Adriatic microplates under Italy from east to west, whilst from the south to the north the convergence of Africa against Europe builds the Alpine orogen and opening the Tyrrhenian sea to the west of the Italic peninsula.  

I won’t extend much in this entry; you can read better and more updated information in the news:


Sadly an Italian geophysicist predicted the event –kind of–. We cannot rely on predictions. We cannot expect –yet– to trust correlations between indirect measurements and seismic phenomena. What we can do?

What we can do as geologist is help the authorities educating people, promoting the knowledge of geohazards and how to behave in the case of an Earthquake. Authorities have in their hands the power of approve correct standards for construction. A 6.3 earthquake shouldn’t have caused any fatality in a rich country like Italy. Why it has been like that? Seismicity in the Central Apennines is not new. Historic earthquakes include the one  of 1997 (Mw 6.0) which includen in a period of 2 months several M5.0 events (the Umbria-Marche seimic sequence).

Our support to the people in despair for this earthquake.

(Later I will update this article with some images and corrections... I am sending this from my email!)




Wednesday, 25 March 2009

Tonga and bad science

0 comments
In the recent weeks we have witnessed through the media the eruption of the Tonga submarine volcano reaching the oceanic surface. Spectacular images make us feel small in this wonderful planet. The volcano is emerging day after day and, as reported by Associated Press, it is located at 10 km from the main island, Tongatapu, in a cluster of nearly 60 other volcanoes.

A few days after after the volcano got protagonism, the media also informed of a relevant earthquake in the area, happened on the March 19th, 2009. A 7.6 magnitude earthquake shaked the conctact between the Pacific, also in the vicinity of Tonga.

Well. No. Not really. I mean, yes, it happened, but not in the "vicinity of Tonga". It happened 260 km of the location of the volcano. Anyone with a slight knowledge of geology would think: "Yeah, they are close, relatively, but surely not related at all".


This thought didn't pass through the mind of the responsible of choosing the title of the news in the BBC website...: Quake may have caused eruption. Well, why do they choose this title if the video doesn't make any connection between both events? Very few people would have seen the video (hey, it's science, not a celebrity in Cannes), and most of the readers have kept in mind just that: The earthquake and the volcano may be related.

It is hardly explainable how an earthquake in such a tectonic framework (an oceanic convergence) can cause, or trigger, or affect a volcano 250-300 km away. Both phenomena are perfectly understandable if we take them independently. So, why the story in the news? Possibly is easier to sell the story like that.

I remember how difficult is to explain people how two events can happen at the same time but be absolutely independent: "Sorry, are you saying that the tsunami in Sumatra is not related with global warming? but... surely is related. We destroy our planet! And anyway, you work with satellites, you haven't been in the field". Argh.

Anyway, the good news is that there is not any material harm, and general news are talking about geology. Woohoo.

(Reading about the Tonga volcano and the earthquake I got know the blog of Maria Brumm, "Green Gabro". Take a look, is well worth doing it)

Monday, 2 March 2009

Virtual Seismic Atlas

0 comments
During the 80's the explorationists had in their shelves the unique work of A.W. Bally, "The Seismic Expression of Structural Styles", published by AAPG ("AAPG Studies in Geology" series). This atlas presented and explained in several volumes different seismic lines of all around the world and touched all different types of deformation and deposition. But new times mean changes. Geology isn't an exception to this rule, and for a few years we have available online the Virtual Seismic Atlas.


The Virtual Seismic Atlas is an independent and free project based in contributions by public and private organisations and companies. It collects paradigmatic examples of seismic in differente regions, tectonic / sedimentary frameworks, deposition environments, etc. It is possible to browse it using different criteria (environment, types of structures, depositional environment and so).

http://www.seismicatlas.org/

The Virtual Seismic Atlas is sponsored by BG Group, Shell, BHP Billiton, StatoilHydro, HESS, NERC and PESGB. It also counts with the collaboration of British Geological Survey, The Geological Society, CGG Veritas, Fugro, Badley Geoscience and Midland Valley. The project director is Rob Butler, and it is hosted in the servers of the Universidad de Leeds.


Thursday, 19 February 2009

Software for stereographic projection. Stereonet

25 comments
It is never a bad idea to refresh our memory about the software available online for free (freeware, GNU licenses, etc) in our profession. I have thought that it would be a good idea to dedicate some posts in our website to that topic. So we start today with...:

Software for stereographic projection

There are several pieces of software that you'd like to check out for that purposes. Basically all of them do the same job: project, display, analise and modify orientation data on a stereonet. More in detail, you can project in equal area, or you can choose to project in equeal projection. You can choose the hemisphere (high or low), you can choose to work with a pole or with a plane projection... And of course, rose diagramas, changes in directions for palaeocurrents, etc.

As we know, that is a basic procedure in structural geology, and therefore, my first recommendation is to masterise the stereonet by hand, using (oh, yes!) drafting paper, a pencil and a paper stereonet (And a flat pin, of course*). It is not difficult at all, and it can be fun. I loved it during my degree.

OpenStereo: Reviewed in one of my articles here: http://www.structuralgeology.org/2011/01/openstereo-stereographic-software.html. So far, I am really impressed by it!

Stereonet
(by Rick Allmendinger): In his website you can download not only Stereonet, but a fair amount of other useful tools. For non commercial purposes. It is my favourite one, as it works very well, and I haven't found any bugs in it. Go here: http://www.geo.cornell.edu/geology/faculty/RWA/programs.html

StereoNett: German software produced in the University of Bochum. This is the old version, but perhaps it can be still useful in some old machine... anyway the new version is Stereo32, that you find in this article, below :-) : http://www.ruhr-uni-bochum.de/hardrock/downloads.htm

Stereo32: Same software than the one mention above, but rewritten and designed for Windows 2000, XP and Vista: http://www.ruhr-uni-bochum.de/hardrock/downloads.htm

If you know more software, please mention it in the comments of this article and I will add it to the list.

Soon, more software...

____________
* That reminds me my lessons of "Structural Geology" in the second year of my degree. I studied Geology in Spain, where the basic degrees was, and still is, 5 years. Two of my classmates had exactly the same results during a test, and the lecturer knew perfectly who copied from who: one of them presented his drafting paper without a hole in the center for the pin!!
:-)

Sunday, 15 February 2009

Congress: Salt tectonics, sediments and prospectivity

0 comments
I joined the Geo-Tectonic mail list (www.jiscmail.ac.uk/lists/geo-tectonics.html) several years ago and, in my opinion, one of its most useful features is the contribution of news about congresses and meetings related with structural geology and adjacent areas (of knowledge!).

In this case, Ian Alsop has sent the information related with a very interesting congress on salt tectonics, titled "Salt tectonics, sediments and prospectivity", due to be celebrated in The Geological Society next January. Not a long way, after all!


Salt Tectonics, Sediments and Prospectivity
International conference sponsored by The Geological Society, Petroleum Group and SEPM
January 20-21st 2010
The Geological Society, Burlington House, Picadilly, London.
This two day international conference aims to bring together academic and industrial geoscientists to review recent advances in our understanding of halokinetic processes and to explore the links between salt tectonics and sediments. Encouraging the interaction between structural geologists and sedimentologists is a desired outcome. Contributions are invited that address key technical issues that include:
  • How does salt tectonics manifest itself in sedimentary basins?
  • Comparisons of subsidence rates between tectonically generated basins and salt withdrawal minibasins?
  • Prediction of reservoir presence and quality and new generation facies models
  • What traps hydrocarbons in salt flank structures – salt side seal or sand pinch out?
  • Salt as a trapping and breaching mechanism – are salt welds sealing or leaky?
  • To what extent does salt suppress hydrocarbon maturation?
  • What role does salt play in sandstone diagenesis?
  • Sub-salt imaging – how far have we come, new approaches / techniques to make further improvements?
  • Papers are welcomed from a wide range of sub-disciplines including, earth surface processes and landforms, outcrop or mining data, subsurface seismic, well and core data, potential fields and physical and numerical modelling.
More information, abstract deadlines and posters to download etc may be found at our web page:
Convenors
Stuart Archer ( University of Aberdeen)
Ian Alsop (University of Aberdeen)
Adrian Hartley (University of Aberdeen)
Neil Grant (ConocoPhillips)
Richard Hodgkinson (Bowleven)

Tuesday, 3 February 2009

Trishear deformation: the yet to bloom concept

0 comments

We are used to draw fault related folds using graphic methods involving kink folding and parallel folding. This methods allow us to get an idea of the folding mechanism ruling some structures, but in general nature is more complicated than that...

Rick Allmendinger, structural geologist from the Department of Earth and Atmospheric Sciences at Cornell University explains it in full in his website :-)

What the heck is "Trishear," anyway?
Eric Erslev (1991) deserves full credit for developing the concept of trishear. During his studies of the Laramide Rocky Mountain foreland in Colorado and Wyoming, he noticed that discrete fault zones within the basement diffuse outward and upward in a triangular zone of deformation in the overlying sedimentary section. He called these triangular zones of deformation "trishear." Trishear provides an alternative to the parallel kink fold description of fault-propagation folding. Unlike the simple kink fold model, trishear can produce footwall synclines, downward steepening dips and thickening and thinning of forelimb strata. Furthermore, trishear provides a richer description of heterogeneous strain distribution at the tips of propagating faults (see the above graphic), which may ultimately prove useful, for example, in studies of fracture distribution and orientation. However, whereas parallel kink fold angular relations can be determined graphically (e.g., Suppe & Medwedeff, 1990), trishear models can only be calculated numerically.
Since 1997, we have been studying trishear extensively at Cornell and have concluded that trishear structures are far more widely distributed than previously recognized. We have written general 2D and pseudo-3D trishear modeling programs which enable us to explore the complete broad range of trishear-associated deformation In these web pages, we give a brief, mostly graphical, introduction to trishear, with the intent of illustrating how it might be used. Be sure to check out the trishear movies!
This material in this site is partly based upon work supported by the National Science Foundation under Grant No. EAR-9814348. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF). Additional support comes from the Donors to the Petroleum Research Fund of the American Chemical Society. And finally, there is a lot of unsupported stuff in here as well :-)
I think a good understanding of this concept should be a requirement to anyone approaching structural geology in a degree. Unfortunately, it doesn't seem to be a very spread idea yet. So you know... Visit it, play it, learn it!

http://www.geo.cornell.edu/RWA/trishear/default.html

Monday, 2 February 2009

Online sale of the GeoSoc bookshop: February'09

0 comments
Hopefully you don't read this message too late!

The Geological Society of London, through its bookstore service, offers periodically at a very low price different volumes in an online sale. The volumes belong basically to the Special Publications series, amongst others.

In this occasion the GeolSoc runs the sales from 30 of January to 6th of February of 2009; but don't worry, this sales are repeated every 2-3 months.

This time most of the books are offered at £25 (sales price for the last years, as far as I remember), and having in mind the quality of the titles, this is a real bargain.

Check it out here: http://www.geolsoc.org.uk/gsl/publications/bookshop/SalePublications

Box Cube Cut

0 comments
My friend Raik sent me last week this video from YouTube, a very funny presentation that, from a very cinical point of view, shows us the... reality behind software in the Exploration and Production world :) Read carefully the introduction to the video.

Sunday, 1 February 2009

Great set of paleogeographic maps

1 comments
Who doesn't surf the net and find very interesting links that after a couple of days are totally forgotten? Some days ago I found this superb collection of paleogeographic maps in the website of Dr Ron Blakey.

http://jan.ucc.nau.edu/~rcb7/globaltext2.html


The globes presented in this series show how Earth may have appeared over the last 600 million years (Ma). The global views were prepared from rectangular projections drawn at a resolution of 3000x1500 pixels for each of the 26 time slices (small files of the rectangular maps are also included). Topography was "cloned" from digital elevation maps of modern Earth from the USGS. Colors were adjusted to portray climate and vegetation for the given time and location. The modern Earth was also drawn in this manner using a color pallet derived from satellite images created by ARC Science of Loveland, Colorado. The geologic data was gathered from the references listed below. The completed rectangular images were then wrapped on a sphere and saved as jpg files.


Take a look. They don't only look great, they show great geology. Enjoy it!

Friday, 30 January 2009

Welcome!

2 comments
Welcome to this website about structural geology. Why we do it? Because we like Earth sciences and we like to understand the processes which model the crust and the upper mantle of our planet. And more important, we like to discuss about and to spread what we know.

Perhaps you have arrived here because you don't know what is this all about. Structural geology and tectonics are sisters, much closely related than other disciplines within the Earth sciences constellation of knowledge, but not so different.

Structural geology deals with the deformation of rock units, how different stresses affect rock bodies causing a certain strain, and how this stress and strain are distributed in space and time. Tectonics is the study of the deformation within the Earth's crust, and its consequential structural effects. In ther words, structural geology deals with the micro and mesoscale of deformation, and tectonics deals with the macro- and global scale of deformation.

Both structural geology and tectonics will have their home in this website where everyone is more than welcome. Regardless of the level of experience you have in this disciplines you are welcome to collaborate, to discuss, and why not, to sit down and read.

If you want to contact us, just email to info @ structuralgeology.org .

J.