Talk:Fault (geology)

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webpage on faults[edit]

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

Fault Causation[edit]

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 (talkcontribs) 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[edit]

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[edit]

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?[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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

Images[edit]

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?[edit]

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[edit]

Geologic faultFault (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[edit]

  • 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 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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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 (talkcontribs) 02:34, 29 June 2013 (UTC)

"Earthquake Hotspot"[edit]

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"[edit]

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[edit]

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) Farm field offset along fault trace.

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)
Wallace Creek offset across the San Andreas Fault.png
  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)