Wikipedia:Reference desk/Archives/Science/2015 July 25

= July 25 =

Mountain building before plate tectonics
How did scientists explain mountain building and earthquakes before the theory of plate tectonics became widely accepted?


 * Plate tectonics is indeed relatively recent. But erosion and Deposition_(geology), sedimentation, etc. were worked out long before that. See Uniformitarianism for some background. We also have fairly good articles on history of geology and timeline of geology. SemanticMantis (talk) 06:08, 25 July 2015 (UTC)


 * See also Geosyncline. ←Baseball Bugs What's up, Doc? carrots→ 06:09, 25 July 2015 (UTC)


 * The emphasis was originally on vertical tectonics - unsurprising considering most geoscientists thought that the continents were fixed. The evidence for lateral shortening, however, in the Alps, the Scottish and Scandinavian Caledonides and the Rockies convinced many that the earth was shrinking as it cooled, causing mountain ranges to rise - see Diastrophism and Timeline of the development of tectonophysics (before 1954) (the latter has issues, but it has some useful information). Mikenorton (talk) 11:31, 25 July 2015 (UTC)


 * Mountain building can also be explained by vulcanism. Of course, not all mountains are built that way, but some early geologists might have thought they all were. StuRat (talk) 15:40, 25 July 2015 (UTC)


 * That was the argument of the plutonists, such as James Hutton, who explained everything in terms of vertical movement due to magma emplacement, see also here. Mikenorton (talk) 16:18, 25 July 2015 (UTC)

Has anyone researched levee failure due to earthquake ground motion?
I've tried looking online for scenarios with models that calculate probabilistic levee failure in Vancouver Canada due to earthquake ground motion, without any success. Does anyone know of such scenarios? I found a scenario with a model calculating probabilistic levee failure due to tsunamis, but not one due to earthquake ground motion.Philly underwater (talk) 13:38, 25 July 2015 (UTC)
 * If you want people to reply, make the title of the thread more informative - researched what. Oh, and please sign your post. DrChrissy (talk) 13:22, 25 July 2015 (UTC)


 * University of British Columbia at Vancouver hosts one of the world's top geology, geosciences, and geological engineering programs in the world. Surely there have been hundreds of research projects regarding their local geology and civil infrastructure!  Maybe a good place to start is the UBC Geological Engineering program website, and in related departments.
 * For example, I found Applied Science 170, an introductory undergraduate course they offer (at the Okanagan campus) in case studied of engineered systems failures. Here is their additional bibliography, which includes studies of dam and levee failures in the Pacific coast region.  Some of those resources point to American (rather than Canadian) studies.  For example, from the Teton Dam article, (whose failure was not due to earthquakes - but spurred a major study of dam failures in the entire Western United States), I found the Pacific Northwest Region Safety of Dams program, an ongoing research program of the United States Bureau of Reclamation - the other major government agency that manages water projects and dams in the U.S.  Between this website and the websites of the U.S. Army Corps of Engineers, you can find just massive quantities of research and data on dam and levee safety.  Here's an entire book: State of the Art for Assessing Earthquake Hazards in the United States (1995).
 * Nimur (talk) 14:35, 25 July 2015 (UTC)

But none for canada24.207.79.50 (talk) 17:22, 25 July 2015 (UTC) I was thinking more of scenarios written by companies that do catastrophe modeling24.207.79.50 (talk) 17:34, 25 July 2015 (UTC)

I think I should ask again, but in different wording.24.207.79.50 (talk) 21:18, 25 July 2015 (UTC)


 * Are Canadian earthquakes really that different from everyone else's tremors? The first half of Nimur's post is all about Canadian sources. Roger (Dodger67) (talk) 09:24, 27 July 2015 (UTC)

Sphere formation
What is the name for the phenomenon when a celestial body is massive enough so that it becomes a sphere? Th4n3r (talk) 16:07, 25 July 2015 (UTC)


 * Hydrostatic equilibrium apparently. Mikenorton (talk) 16:12, 25 July 2015 (UTC)
 * Yes, as mentioned in List of gravitationally rounded objects of the Solar System. ←Baseball Bugs What's up, Doc? carrots→ 16:14, 25 July 2015 (UTC)

1 2 3 Void burn (talk) 16:14, 25 July 2015 (UTC)

Dextrocycloversion and Laevocycloversion
In answering an earlier question, I was reading Eye movement - where it describes our ability to rotate our eyeballs not just left and right, up and down - but also to rotate them clockwise or anticlockwise about an anterior/posterior axis! (So that the top of your eye moves towards your nose while the bottom moves away from it).

I was totally blown away to discover this because it's not obvious that we can do it...and I can't think of any reason why we'd evolve to be able to do it. But This article shows the pair of muscles on each eye that are responsible for doing rotating our eyes that way (they are the "Superior oblique" and "Inferior oblique" muscles).

The motion is called Dextrocycloversion and Laevocycloversion - but web searches on those terms don't produce anything other than dictionary definitions of those terms that describe (often poorly) what this motion is and what muscles produce it.

Clearly we don't have conscious control over this motion as we do with the left/right and up/down axes. Standing in front of a mirror, tilting my head to one side or the other doesn't seem to result in any such motion. You'd think that doing it would result in the horizon spinning clockwise and anticlockwise in front of you!

I really find it hard to believe that this is true - but the muscles clearly exist - and the name for the motion is in every medical dictionary!

So - the obvious questions:


 * 1) Am I totally misunderstanding these terms?
 * 2) Why do we need this kind of motion?
 * 3) Is there a way to produce the motion so we could observe it happening?
 * 4) By how many degrees can the eyeball rotate in such circumstances?  (I'm guessing it's a tiny number...but who knows?)

SteveBaker (talk) 18:34, 25 July 2015 (UTC)


 * "The chief function of the two oblique muscles is to rotate the eye on its own principal axis to keep the horizontal level in certain head movements, but since the eyeball is radially symmetrical this movement is not easily observable." Wendell J. S. Krieg, ''Functional Neuroanatomy (Philadelphia: Blakiston, 1942),pg. 68.&mdash;eric 21:05, 25 July 2015 (UTC)


 * Interesting. When walking with a normal video camera, the video is rather painful to watch, as it bounces about (hence the invention of the steadicam).  We don't observe this when walking ourselves, though.  Presumably the brain does a lot of image stabilization, but, since it's not enough to fix the video, there must also be some other mechanism to keep the image from bobbing about.  I suspect that this is where those muscles come in.  They might even predict your next step and act accordingly, as you make it, to avoid a delay that would wiggle the image.


 * Also, I suspect that some birds lack these muscles, since they keep their head steady as they walk, then suddenly move it to a new spot, then hold it steady again. A much cruder way to stabilize the image. StuRat (talk) 21:14, 25 July 2015 (UTC)




 * This abstract may help in answering #4. Cyclotorsion seems the best search term.&mdash;eric 21:31, 25 July 2015 (UTC)


 * See the last part of the "Torsion" section of this article for #3 and #4.&mdash;eric 22:16, 25 July 2015 (UTC)


 * Searching for Ocular countertorsion i think answers everything.&mdash;eric 01:01, 26 July 2015 (UTC)