Talk:Fault (geology)

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This article was the subject of a Wiki Education Foundation-supported course assignment, between 5 September 2019 and 3 December 2019. Further details are available on the course page. Student editor(s): Rockjockey222.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 21:13, 16 January 2022 (UTC)

webpage on faults

When I visited the webpage http://www.wikipedia.org/wiki/Geologic_fault, I was very glad that I had finally found a webpage on faults, but I was really confused by the language. Something that a long-ago English teacher once said to me: When you answer an essay question, tell all the facts you know, make the answer as complete as possible. Then say what that means. ex. "The Earth is an oblate sphere. THIS MEANS that the Earth is a sphere, but because of the fact that it spins on an axis, centripical force flattens the poles and pushes out the center. A good way for you and I to understand what this means is by thinking of a popular toy much like a yo-yo. This toy is a, viscous disk about 1 cm thick and 4cm in diameter. It is attached to two strings coming out of either side. One twists these strings, then untwists them with a flick of the wrists, repeating this motion until the circle blurs, appearing bigger than it is. In truth, it is not an illusion, but that the centripical force has pulled the edges of the disk out with material taken from the top and bottom of the disk, forcing it to squish in. This is how the Earth acts." I am not saying that the explanation of each fact should be as complete as this one– no, for that much information would be much too much. However, in the way that this explanation makes you understand (or at least tries to), you don't have to be comfortable with scientific language. If you understand the part quoted about the toy, you don't even have to be able to think abstractly. I think that your geography page could do well to be written in some way more similar to this.

It's a geology page, rather than a geography page, but fair point. Will have another crack at it. charlieF

I second the point made above: the earth link in the lede takes you to earth as in the planet, when this is clearly not meant. Many geology pages could do with more diagrams so that the uninitiated can understand the terminology better. Geology students: Help us!1812ahill (talk) 00:25, 2 May 2015 (UTC)

Fault Causation

Next to the Strike-slip Faults section, the description under the image of the San Andreas Fault suggests that the fault caused the earthquake. This is not true. Earthquakes cause faults, not the other way around. —Preceding unsigned comment added by Iraubergeek (talk • contribs) 14:59, 7 April 2010 (UTC)

So can you explain how you get an earthquake to occur in a solid object. The fact is they cannot - faults progress by brittle failure into solid structures, exploiting zones of weakness. Earthquakes occur as a result of a fault locking and then suddenly moving. Every earthquake plots onto an existing fault plane not the other way round.The Geologist (talk) 16:24, 22 July 2013 (UTC)

Hangingwall/Footwall

I am (was) trying to learn about terminology of structural geology. I found this web page and read it, and thought I understood it. Then I visited another site, the Schlumberger oilfield services oilfield glossary page about faults. I thought I understood what a hanging wall was from this page since I could grasp the concept of 'the block above the fault' easily. What I mean is that I had an 'intuitive' feeling for the concept of a fault plane (as long as it wasn't vertical) and could easily grasp the idea of the block above this plane and the one below it. Then I went back to this page and realised that according to the Schlumberger definition what is called the hanging wall here I would call the footwall and vice versa. I don't understand why. Don't forget I'm an amateur and could be missing something obvious.

I'm pretty sure the caption on the picture is backwards and the Schlumberger source is correct. Can anyone think of a quick fix? -- Walt Pohl 16:56, 17 Mar 2004 (UTC)

I agree. I can't find a web page that agrees with our picture, so I swapped the labels. -- Heron 21:24, 17 Jul 2004 (UTC)

I hope that the mining origin of the terms helps people, it sure helped me Mikenorton 16:49, 15 October 2006 (UTC)

integration

Text copied from newly created article 'Faults'. Maybe there is something that ought to be integrated into the article:

A fault is a fracture in the crust of the earth that has caused displacement (offset) of the crust. Faults may offset soil or rock materials on either side of the fault plane for distances ranging from less than a few inches to distances on the order of hundreds of miles. Faults are usually associated with past or present tectonic movement, seismic activity (earthquakes), and volcanic activity. Faults may be quite old features (having displaced rocks millions of years old) to recent features that have displacement rocks within historic times. Faults may be too old since their last displacement to be of concern to man, whereas recently active faults, particularly those faults associated with recent large earthquakes, can be a significant hazard to man.

- snoyes 11:35, 5 Jul 2004 (UTC)

Reverse fault same as thrust fault?

Some texts, unlike our article, make a distinction between reverse fault and a thrust fault. A reverse fault is the exact opposite of a normal fault, while a thrust fault is the slippage of two strata past each other under horizontal compression. Is this distinction generally accepted? -- Heron 21:40, 17 Jul 2004 (UTC)

Many structural geologists would use "thrust fault" for a compressive fault dipping LESS than 45 degrees and "reversed fault" for a compressive fault dipping MORE than 45 degrees. User:Denbrok

Thrust faults, as Denbrok said, are shallow-dipping. They also have other distinguishing features from reverse faults, in that they occur within units; ramp up through units; may be associated with fold-bend folds, etc etc.Rolinator 02:38, 20 December 2005 (UTC)

Depending on who you ask the amount of dip at which a thrust fault is called reverse fault and vise versa varies. a common value is 35 degrees. EndoSimon 12:12, 16 April 2007 (UTC)

The fault labeled in Figure 3 as a 'thrust fault' looks more like a reverse fault. Perhaps a better image could be located. PowerWill500 (talk) 23:17, 3 September 2008 (UTC)

Removed Image:Fault types.png as it is in error. Yes the USGS can make errors. Vsmith (talk) 23:51, 3 September 2008 (UTC)

Whilst a thrust plane is an over-riding of the lower sequence and places older rocks on top of younger ones, it is not to be confused with a reverse fault which, whilst it apparently does the same - older rocks over younger rocks, they are distinctly different. A reverse fault usually has a high angle ~>40 degrees whilst a thrust generally is considered to have a low angle ~<30 degrees. Thrusts are usually associated with large tectonic motion at subduction zones. It was the mapping of the Moine Thrust - NW SCotland, in the 19th Century that proved that (despite the theory advanced by many geologists of the time), it was impossible for metamorphic rocks to be deposited above unaltered sediments and then undergo metamorphism leaving the underlying rocks unaffected.

Incidentally the term "normal" and "reverse" in respect of faults originated in the British Coalfields. Miners could tell which way the seam had moved and as the usual direction was downwards it was considered to be "normal" to then dig down until the coal seam was encountered and on occasions the opposite was the case and this said to be reversed motion or a reverse fault.The Geologist (talk) 16:24, 22 July 2013 (UTC)

Merges

I think transform fault and thrust fault should be merged into this article. If they get too big, they can be split off again. -- Kjkolb 03:39, 16 December 2005 (UTC)

I think not; they are too different in terms of their sense of throw and geologic setting. Thrust faults are not at all like transform faults.Rolinator 02:36, 20 December 2005 (UTC)

I know they are very different, but normal faults, reverse faults, strike-slip faults and oblique-slip faults are covered here and don't have articles of their own. Transform fault is only a paragraph and one sentence long and thrust fault is two paragraphs long, and the second paragraph is small. Both are shorter than the dip-slip fault section of this article even without the pictures. -- Kjkolb 08:30, 20 December 2005 (UTC)

No, let's keep them separate. Both thrust faults and transform are distinctly different from other fault types and each other. They describe totally differing geologic processes and the articles for each need considerable expansion - definetly not merging. Vsmith 03:30, 21 December 2005 (UTC)

That's fine. It just seems weird to have some fault types split off, while other major types are included in the article, especially when the articles are so short. I'll remove the tags. -- Kjkolb 06:17, 21 December 2005 (UTC)

There's talk on the [[1]] page to merge its content with this page. My question is whether the terminology "Earthquake Hotspot" is a legitimate geological term. In my experience it is not, but more learned folks might want to check the page out and make a recommendation. Mkantonelli1 (talk) 10:48, 12 February 2012 (UTC)

Duplexes, ramp-flat, klippe

I have added throw, heave, etc. Added duplexes and klippe. I'm lacking decent open-source diagrams for these, especially the ramp-flat ones.

Parallel Faults

I was reading about dip-slip faults, and got confused about the use of the word "parallel". It seems that the author means parallel at the surface. I looked at the linked articles for horst and graben, and found the same reference to "parallel" faults, but the fault planes are not parallel, only the intersection of the planes with the surface. Is this a standard accepted use of this word in this context? Also, as a geology neophite, I wonder if three or more faults could produce the same effect as a horst or graben, without even the intersection of the faults and the surface being parallel?

Yeah. Imagine a graben within a graben. In fact, that's what happens pretty much all of the time, since faults always come in sets. "Parallel" must indeed refer to the intersection of the fault plane with the surface, but even then it's not a precise term. A horst or graben can be between two fault planes which do not have parallel strikes... just so long as they're roughly parallel and not, like, perpendicular.

I added the dip directions of the two faults in the horst and graben definitions and then decided that the use of "parallel" became unnecessary. Mikenorton 16:52, 15 October 2006 (UTC)

syndepositional faulting

Editing something else. Need to put SynDep faulting onto the To-Do list. Really needs a diagram to help.

Images

The amount of images people have taken of "a fault in the wilderness" is flattering as to the importance of this page, but the following image, in thumbnal, is pretty much useless as far as a clearly legible depiction of faulting goes, so I have removed it from the page;

Relative Motion

This is not to say it isn't a good photo, but for illustration purposes we need things which are clearly identifiable as faults even in thumbnail size.Rolinator 23:52, 26 October 2006 (UTC)

I agree. I can tell the fault is in the middle of the photo, but someone who doesn't know a thing about geology would not see it. Mkantonelli1 (talk) 10:51, 12 February 2012 (UTC)

Thrust / Reverse faults definition incoherent with pictures?

There must be a slight inversion here. In one of the pictures, a reverse fault is shown, but labelled "thrust fault". In another one both names are used. This perhaps may be changed for a clearer version.

Requested move

Geologic fault → Fault (geology)

• You won't find the term "geologic fault" in any dictionary or other encyclopedia. In keeping with general naming style in wikipedia I'd suggest changing the name of the article to "Fault (geology)" (with redirect from geologic fault). If no discussion I'll do this soon. --Zamphuor 13:49, 21 April 2007 (UTC)

Discussion

• Support: This is a sensible suggestion. (John 14:21, 21 April 2007 (UTC))

• Support: Term used exclusively by geologists and geological engineers; give'r. +mwtoews 02:03, 22 April 2007 (UTC)

• Support: "Geological fault" redirects to this page so Zamphuor's suggestion would be a good plan - either that or I think the fact that this term is also used to describe this feature needs to be incorporated into the article. --Vertilly 12:15, 20 May 2007 (UTC)

• Support. Neither the phrase geological fault nor geologic fault is common English, rather the context indicates that this is the meaning, so this is a standard case of disambiguation. Andrewa 03:09, 13 August 2007 (UTC)

• Support Sdornan 03:12, 14 August 2007 (UTC)

• Support Rolinator 05:09, 14 August 2007 (UTC)

• Support Mikenorton 10:14, 14 August 2007 (UTC)

• Support Geologyguy 13:54, 14 August 2007 (UTC)

• Support per nom Reginmund 01:37, 15 August 2007 (UTC)

Moved per consensus. Will fix double redirs. now. Vsmith 02:56, 15 August 2007 (UTC)

Mitigation

I'm not sure what this section is doing in this article, this is covered better by the pages on Seismic hazard and Mitigation of seismic motion. Unless anyone objects, I'm just going to add these links to the See Also section and remove Mitigation.Mikenorton 08:22, 15 August 2007 (UTC)

No objections, so section removed. Mikenorton 16:06, 16 September 2007 (UTC)

fault plane

This topic is in some kind new to me, but as I have not found any article mention 'focal mechanism' I would suggest that an article should be created and 'fault plane' should lead there or should be the article title, which in the latter case treats 'focal mechanism' as well. Ausgerechnet alaska 02:20, 15 September 2007 (UTC)

INCLUDE EXAMPLE OF NORMAL FAULT

Figure 5. Schematic illustration

Can someone fix/move Figure 5? It covers a portion of the image of the San Andreas fault and it's caption. I'm not sure how to reduce its size, otherwise I'd do it myself. THANKS!! 66.218.202.75 (talk) 19:24, 29 July 2008 (UTC)

Include mechanics of faulting

Should we connect this to the more quantitative mechanical explanations for faulting, especially as given by Mohr-Coulomb failure? Awickert (talk) 02:46, 27 September 2008 (UTC)

Slip, heave, throw

An anon IP has been removing the "Slip, heave, throw" section without explanation, and adding ambiguous text, worsening the intelligibility. They were reverted [2]. Another editor (probably the same anon IP after logging in) has removed the same section without explanation, and added more ambiguous text with elementary grammatical errors. I have reverted.

I think the article needs a section like this, but it needs to be reworded to make clear what it is trying to say. Removing the section without explanation is not helpful. The section needs to have an intelligible explanation of what "sense of slip" actually means with citations to reliable sources. 85.94.186.91 (talk) 15:43, 6 September 2009 (UTC)

Nuclear Plant

According to this the North Anna Nuclear Generating Station was built on a fault line. — Preceding unsigned comment added by 85.177.152.21 (talk) 09:04, 24 August 2011 (UTC)

Slickensides, slickenfibres

Hi, I am a student of the OU, UK, in Geoscience, from Germany. Your side is more extensive than the german ( Verwerfung (Geologie)). What is about "slickensides" and "slickenfibres" in connection with the topic "fault plane"? "They developed, when the fault was active; fibres form when the walls are held apart by mineral-rich fluid under pressure, grooves form where they are not. The grooves themselves are called slickensides, whilst the fibrous mineral growths are often called slickenfibres. Slickensides and slickenfibres give an accurate measure of the direction of slip of the fault." [ which occured at last] The Open University, S 260 Geology, Block 3 Internal processes, Walton Hall, Milton Keynes, MK7 6AA, first published 1999 I do not want to try to put it in the article, because my style in English is not a perfect one. --Schuetzler 62 (talk) 16:59, 28 December 2011 (UTC)

I've moved this question to the bottom of the page and given it a title for clarity. Slickensides should be mentioned - we need a section on determining fault displacement or something similar. I will try to remember to do it when I get the time. Mikenorton (talk) 17:07, 28 December 2011 (UTC)

Isopach map

A map, which say that it's an isopach map, has been added to the article and is now the first image. A number of questions (with my views added):

• Should it be the first image that visitors to the page see? - probably not, I think that the outcrop image of the Blue Anchor fault is much clearer
• Does it add anything to the article? - it's not clear to me that it does, it's not possible to read the contour values so you can't tell which is up or down across the fault or how much displacement there is, assuming that you know what such a map means
• Is it really an isopach map? - it looks like a depth structure contour map on a particular stratigraphic level to me, in this case I'm assuming 'top reservoir'

On balance, I would remove this, but I will await other comments. Mikenorton (talk) 16:07, 27 April 2012 (UTC)

I'll go ahead and move the Isopach map image.

It would be better to have a higher resolution image, so that the specific elevations numbers can be read.

I'll find a better underground map with a fault line to post, and posit it in the future, in high res. RainmakerUSA 03:03, 30 April 2012 (UTC)

Outcrop explanation from de wiki

I reverted the addition of the text and pictures that were based on those used in the German version of this page. I looked at the pictures there, but I don't find them or the text at all helpful in understanding the outcrop effect of dip-slip faults - you can see them here - others may disagree. Mikenorton (talk) 20:43, 15 October 2012 (UTC)

Not helpful, OR, and WP is not a "how to". Vsmith (talk) 00:19, 16 October 2012 (UTC)

Subduction zones

Unless I'm mistaken, arn't subduction zones faults? They don't seem to be discussed in the article. Volcanoguy 07:19, 30 November 2012 (UTC)

They are in fact the biggest fault zones on the planet. The whole article needs a rewrite, although I'm not too sure where to start. It needs a section on why faults form, how fault networks develop from individual fault segments, why they cause earthquakes, their economic importance (e.g. association with mineralisation) and no doubt other things that I can't think of right now. One of these days I'll get round to doing this, unless someone else beats me to it. I'll try to add in subduction zones though right now. Mikenorton (talk) 17:39, 30 November 2012 (UTC)

You know what I do, I just remake articles from scratch as if you're making a new article. Start collecting information and put in your sandbox and when you are done with it just copy and paste it into the article's text box then save it. I can't remember the last time I did that but it may have been the Mount Price article. Actually, I'm in the process for doing it again to remake and expand the Itcha Range article. Volcanoguy 19:54, 30 November 2012 (UTC)

I would not call subduction zones faults. I would call them plate boundaries where a large number of faults occur. The distinction for me is that the material on the downgoing plate may have absolutely no relation to the material on the overriding plate. There is no way to measure total offset. The directionality of the plate boundary is not as simply related to the direction plate motion as an outcrop fault would be related to the direction of stress. The subduction thrusts (or megathrusts) themselves are very unique faults; a discussion of the subduction channel theory, deep-sourced fluids, sediment underplating, etc, should not be in the main article about faults. — Preceding unsigned comment added by Elriana (talk • contribs) 02:34, 29 June 2013 (UTC)

"Earthquake Hotspot"

To my knowledge this is not a real geologic term. It is no geology glossary or book that I have ever found. The phrase "earthquake hotspot" seems to be found only in a few news articles, where "hotspot" is slang for a place where something happens frequently, just as a graffiti hotspot would describe an alley with a high incidence of graffiti. I believe the redirect to this article should be removed because it seems to validate "earthquake hotspot" as a term synonymous with "Fault".Elriana (talk) 02:45, 29 June 2013 (UTC)

Proposed first step to address "insufficient citations"

This article has been identified at WP:The_Core_Contest as core ("vital") and needing repair. The most prominent repair needed is as tagged: lack of inline cites. I don't feel like doing that whole job myself, but to make it easier for anyone else I propose to move all of the full references out of the text and into the References section, and to create the proper Harv templates for doing short cites in the text. This would simply the editing needed to add the in-line cites. Any objections? ~ J. Johnson (JJ) (talk) 00:02, 11 February 2014 (UTC)

Done. But note: attribution (citation) of specific material is still needed, one citation is dead, and some of the others are pretty flakey. It would be a big improvement if someone were to identify some leading authorities on the topic, and cite from them instead of grabbing what ever Google tosses up. There are good, authoritative sources out there; we don't need to rely on any junk. ~ J. Johnson (JJ) (talk) 01:21, 15 February 2014 (UTC)

Changes

I played hookey today, made some changes here that shouldn't be controversial. I propose another change: deleting the paragraph on accelerating moment release (AMR). That is something more appropriate for earthquake prediction (though even there its notability is suspect); I don't see that it is relevant here. Also: the image for strike-slip faulting doesn't really show that, we need a better one, like shows some offset. I've seen some good images, but off-hand don't have any good "free" ones. ~ 21:59, 15 February 2014 (UTC)

There being no objections, I have removed the section on AMR. ~ J. Johnson (JJ) (talk) 21:05, 20 February 2014 (UTC)

Ha! Perhaps this image will suffice. ~ J. Johnson (JJ) (talk) 23:21, 15 February 2014 (UTC)

It's a great image, showing no vertical displacement at all - the only problem is that it appears to show left lateral movement, although the slip on the Imperial Fault in that earthquake was right lateral. I've also just uploaded a USGS image of the San Andreas which might be better still. Mikenorton (talk) 23:13, 16 February 2014 (UTC)

  Yes, 2/3 of a period dextral movement looks like 1/3 sinistral, lacking any definite piercing points or signs of dragging. That is one point in favor of offset fences, but what I don't like about those pictures generally is that the fault trace is not evident, like it is here. My thinking here is that even if readers misinterpret the slip (and I see this as left-lateral even though I "know" better), it doesn't matter: the point comes across even if it is backward. (Benjamin Franklin is still credited with discovery of electrical current as a flow, even though he got it backward.) I think confusion would arise here only if a reader knows this is right-lateral fault, AND does not understand that +2/3 = -1/3.

  The problem with many of the Carrizo Plain images is either that the fault trace is not clear, or the offset is not clear. I have seen some good, immediately discernable images, usually showing offset of one or two streams. But I haven't found any free ones (yet). There was an article some years ago with good images, which I would ask about, if only I could remember which article. Well, I'll try some different search terms. ~ J. Johnson (JJ) (talk) 22:01, 17 February 2014 (UTC)

Chapter 2 of USGS Professional Paper 1515 (on-line) has a bunch of pictures. Generally not so good, but fig. 2.5 is a good diagram. ~ J. Johnson (JJ) (talk) 22:36, 17 February 2014 (UTC)

I agree that Fig 2.5 is good but so is this. Mikenorton (talk) 23:42, 17 February 2014 (UTC)

Too noisy. I would crop out the upper half to focus attention on the fence. What I like about the first picture is that it doesn't need doctoring to show the fault trace. Also, with all the "fence" images it is never clear that the fence might have been built that way; with fields/orchards/vineyards that is not a factor. ~ J. Johnson (JJ) (talk) 00:05, 18 February 2014 (UTC)

Globalise tag

A tag has just been added suggesting (to quote what appears at the top of the current version of the page) "The examples and perspective in this article deal primarily with the First World and Western countries and do not represent a worldwide view of the subject". In my view faults are faults, wherever they occur - what we need in the article are good examples to help the reader understand the topic, irrespective of their location. As to the perspective, I am not aware of any other 'perspective' to the one currently used in the article. The current pictures are variable in quality - I don't personally get much from either the French example (too much vegetation obscuring the fault) or the Junction Fault (it's just hard to see what the relationship is between the two sides), so I'd be happy to see them replaced. I'll take a look around for alternatives, but the main criterion should be clarity, rather than location. Mikenorton (talk) 11:45, 28 November 2015 (UTC)

Agree and removed tag; it's about geology not social inequity. That said - if a good fault image from a non "First World" location which better illustrates a geologic feature exists - then add it. Vsmith (talk) 13:12, 28 November 2015 (UTC)

Vsmith and Mikenorton. WP:GLOBALIZE applies to natural science also. There is no exception. As I see it the confusion stem from an erroneous belief that the need to globalize overrides the need for good quality, aesthetic and illustrative pictures. And it does not. In the case of two pictures where none is obviously superior to the other in terms of quality, aesthetics and illustriousness the one the globalizes the article most should be preferred. Sietecolores (talk) 09:21, 29 November 2015 (UTC)

I have replaced the photos of the fault in France and the Junction fault with photos that are, I hope, simpler and clearer. I did this before I even noticed this section on the Talk page, and my reasons for changing these photos are the same as User:Mikenorton has given. The photos I found as replacements are not particularly good but I think they are at least an improvement on the removed photos. Of course, if better photos can be found, I'd like to see them in the article. I agree that globalization is secondary to content quality and I also agree that globalization of content is desirable if a feature is shown well in a lesser-known (especially non-US) example. Using lesser-known but good-quality examples helps to counter the misleading impression that the ever-present examples, seen in so many textbooks etc., are the only good examples. GeoWriter (talk) 12:38, 29 November 2015 (UTC)

From Wikipedia:WikiProject Countering systemic bias (to which "WP:GLOBALIZE" redirects): Generally, this project concentrates upon remedying omissions (entire topics, or particular sub-topics in extant articles) rather than on either (1) protesting against inappropriate inclusions, or (2) trying to remedy issues of how material is presented. Thus, the first question is "What haven't we covered yet?", rather than "how should we change the existing coverage? Always best to read the page you are using. Vsmith (talk) 14:55, 29 November 2015 (UTC)

...and thanks to user:GeoWriter for image improvement. Vsmith (talk) 14:55, 29 November 2015 (UTC)

Thanks for the clearer images user:GeoWriter - my only criticism is that we don't have any good pictures of reverse or thrust faults, which is an omission. I've looked through all the ones that I can see at Commons and found none that really do the job of showing clearly the effects of such faults. I find this quite surprising, and I've spent a bit of time trying to find photogenic field examples to take pictures of, with rather limited success so far. Mikenorton (talk) 23:17, 29 November 2015 (UTC)

Listric normal faults

I'm not sure if this deserves it's own section or it should redirect to listric fault. Volcanoguy 15:32, 7 January 2016 (UTC)

It absolutely does deserve its own article. I moved the listric fault bit into the normal fault section yesterday and enhanced the section a bit more yesterday, but listric faults are a world of their own. Britoca (talk) 05:52, 22 July 2024 (UTC)

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New Edits Incoming

To whom it may concern,

a group of graduate students is preparing to make substantial edits to this page. We are working together and doing this exercise as a group project for a class under the supervision of a professor and Wikipedia experts. We wish to keep the overall structure of the page but will be editing some sections for content, moving existing information around, and adding some new headings. Overall, the majority of the information that started on the page at the time of this commenting will still exist after our editing. We are not going to use any controversial talking points or vocabulary and only intend to change something if it can be improved.

Rockjockey222 (talk) 15:46, 15 November 2019 (UTC)

"Fault(geology)" listed at Redirects for discussion

An editor has asked for a discussion to address the redirect Fault(geology). Please participate in the redirect discussion if you wish to do so. Steel1943 (talk) 18:46, 10 January 2020 (UTC)

Separate articles on fault types

Currently normal fault, reverse fault and strike-slip fault all redirect to this article. Thrust fault, however, has its own article and I think that we should be aiming for that for all of the fault types. Mikenorton (talk) 17:19, 9 April 2020 (UTC)

I agree, all major fault types should have their own article, even if basic entries for quick reference. Britoca (talk) 05:41, 22 July 2024 (UTC)

Recent edits

Some of the recent edits are an improvement but some are not. It's made me look again at the whole article and I see a lot of things that could be better. I think that the entire article could do with a rewrite, starting with the "Mechanisms of faulting" section (and the article linked at the top of that section, which definitely needs work). I've spent my entire professional career working on faults and shear zones at a variety of scales across different tectonic settings, which has generally led me to leave this article alone as I have strongly held views about all aspects of the topic. However, I should at least try I think, doing my best to stick with what sources say, rather than "what I know". Mikenorton (talk) 21:56, 21 July 2024 (UTC)

I agree, there's nothing on microfaulting, for example. I particularly dislike the very definition given: "a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements"

I learned that a fault is any joint in which there is detectable slip, no matter the scale, and therefore faults vary from microscopic to continental-sized features, but I did not want to alter the header definition without first consulting the community.

I did a major revamp yesterday on the dip-slip section, including drawing my own additional figures. For such an important topic, it was very poorly organized and illustrated IMHO, including drawing my own additional figures. I hope it's to everyone's liking, but please feel free to enhance it further or correct anything I might have messed up. Britoca (talk) 05:50, 22 July 2024 (UTC)

Remove the "Basin and range topography" bit?

Yesterday as I edited the Normal Fault section, there were mentions of grabens and horst. I added an image for elucidation purposes, but the topic is really a geomorphology matter, not so much a structural geology issue. IMHO, to keep this article lean and focused strictly on faults, mentions about grabens and horst should be removed, no? At the same time, it is a rather short bit that does not take up much space in the entire Faults page, and is linked to its own detailed wikipedia page on the matter. Comments please. Britoca (talk) 06:01, 22 July 2024 (UTC)

I don't really like that USGS horst and graben graphic because it's unlike almost anything in the real world. The basic unit of a rift is the half-graben, which means that in most cases it is accompanied by a half-horst (although no-one uses that term). This is true of the basin and range, which is a remarkable extensional province, and also true of the East Africa Rift, the Lake Baikal rift, the Gulf of Corinth rift, the rift along the Apennines, which is pretty much all the active continental rift zones in the world. If we did cover it, it needs to be accurate at least, but probably best to just leave it out as you suggest. Mikenorton (talk) 23:34, 22 July 2024 (UTC)

Should we place Thrust/Detachment faults under a Decollement Faults section?

Decollement faults are not really slipping along a dip anymore if their motion is occurring on a horizonal fashion. Should we place them both under a new "Decollement Faults" section? Britoca (talk) 06:04, 22 July 2024 (UTC)

The one detachment that I know really well is the Nordfjord-Sogn Detachment. It is low-angle now and was almost certainly steeper when it formed, based on the dip of the sediments deposited in its hanging wall. It apparently cuts right across the complete Caledonian thrust stratigraphy, putting the uppermost thrust sheets against basement with eclogites that have been down to 80 km and back in the footwall. Something like the Northern Snake Range Detachment is a bit different and there's evidence of it being fairly low-angle from the start. What they have in common is being zones dominated by simple shear, juxtaposing unmetamorphosed upper plates against metamorphic lower plates, with large (10s of km) displacements.

Thrust faults are low-angle overall, typically consisting of alternations of shorter, steeper ramps (30°) with longer bedding parallel (often sub-horizontal) flats. This is all about mechanical stratigraphy with the flats along bedding planes located at major changes in lithology - these get described, confusingly, as detachment levels. Thrusts also have large (10s of km) displacements but I don't think that they can easily be grouped with extensional detachments.

Decollements are different again, they're just weak zones along which other faults decouple. In passive margins overpressured shales and salt layers act as basal decollements (or detachments) with linked faulting systems characterised by extensional up-dip back ends and contractional down-dip front ends - there should perhaps be a section on these, they're very well described and understood. In accretionary complexes, there is a basal decollement on the plate interface above the subducting slab. This is of course also a zone of overpressured muds into which the thrust faults within the complex decouple (detach).

This is perhaps a rather long-winded way of saying no to your question but I wanted to lay out my reasoning, such as it is. These faults and fault systems are all, however, examples of non-Andersonian faulting. In the Andersonian world all normal faults start at 60° dip and all reverse faults start at 30° dip and all strike-slip faults are vertical in opposite sense pairs at an angle of 60° to each other. This has been an incredibly useful model for understanding fault formation and orientation and should be in the article but it can't be used in all situations. We could perhaps have a section entitled "Non-Andersonian faulting" or something similar. My thoughts continue to evolve on how to handle this. Mikenorton (talk) 20:59, 22 July 2024 (UTC)