Talk:Seismic wave

Untitled
Surface waves do NOT cause most damage in earthquakes. High horizontal accelerations responsible for most damage are associated with shear waves (S-waves). Some geologists think that, because the surface wave traces are largest on seismograms from distance earthquakes, that surface waves cause the damage. Although the displacement of surface waves is usually higher than that of shear waves at teleseismic distances, horizontal accelerations are highest in the near field when the shear waves arrive, and these high horizontal accelerations do the damage.

This error has propagated through generations of physical geology textbooks.

Some seismologists are looking into a new kind of surface wave called a basin-generated wave, but strong motion seismograms usually reveal that the damaging motions are inconsistent with classical Love or Rayleigh waves, the surface waves well recorded hundred to thousands of kilometers from large earthquakes.

Shear wave amplification and resonance in the soft sediments of deep basins is a well know and understood phenomenon.


 * Hmm... ? - Hamsterlopithecus (talk) 07:24, 7 February 2008 (UTC)

From what I have read in my textbook (google Wave Phenomena, it's a pdf), surface waves are the most severe. 75.26.194.89 (talk) 21:18, 24 January 2009 (UTC)trehansiddharth

You are both right. The confusion stems from the vague notation (which I myself have struggled with a lot -- hence the reason I wrote the "notation" section). S-waves and surface waves are actually two different things. S-waves (the kind that involve shearing) can travel along the surface or through the solid earth. (Similarly P-waves can travel both along the surface or through the earth). It is the secondary waves that travel along the surface that cause the most damage. I added some clarifying words to the main article to help alleviate this problem. Sprunger19 (talk) 18:55, 21 January 2010 (UTC) Sprunger19

Length of Article
In general, I find this article too long and comprehensive, with few outside references. Would it be good for a highschool project? I have started to divide some of these things into 1-page focused articles. These are then good for links in other articles. It's a question as to the 'social purpose' of the wiki ??? --Zeizmic 16:44, 13 December 2005 (UTC)

In my opinion, 'outside references' - I presume by that you mean citations from scientific journals - are not terribly important, or even necessary, if the information presented is accurate (because it comes from direct, first-hand work experience). That is how experts are created, as much as study. I've noticed that some eminent experts - scientists - have been contributing their first-hand knowledge, in various fields. Excellent! Wiki needs 'em. I am never too concerned if an obvious expert in a field does not give references, but just says blah blah blah, this is what it's about. Good for him, or her. That person can condense a lot of information into relatively compact form, and spare other people the long and probably tedious study of that subject. And there are always other people come along and say, this is not quite correct, so it gets adjusted. Or added to. So usually it ends up quite accurate.

Who reads the journals anyway, but the experts? Not very many people! And: citation is a game in itself. There has been strong criticism of the policy of using the number of times a paper is cited as a measure of its quality, for example. Some scientists have said: wrong! (Just to cite the problem with citations.) They are not only used, today, but also abused. "Ha, I've been cited 112 times! Even so: that paper may not be terribly exciting or interesting or valuable or useful.  Yet, citations have become the default rating system.  Foolishly so, in the opinion of some scientists, who I happen to agree with.

Fact is: you can probably find supporting information/references on your own, using Google, if you want it. Type in any term: you can obtain a whole lot of information outside Wiki, about anything. Enough to boggle the mind, and growing rapidly. Wiki should not be considered 'the universe of information'. It's not important that it be 'the authoritative source', as long as the info is well-written and accurate.

In the case of this article...I authored better than half of it, as it stands. That's because I worked in seismology for a number of years. I saw gaps in the article as it was. So I added my knowledge. During my work in seismology I located many earthquakes, using a program I wrote, from scratch. My locations typically agreed very well with the official USGS epicenters, even though I was using data from merely three seismograph stations, and my own equations, which I derived, carefully, from published, well-accepted travel-time charts.

So, that's my reference: personal work experience. Years of it.

Maybe the article is 'too long and comprehensive' in your opinion, but I don't see the harm in being comprehensive, nor any harm in presenting information of a more esoteric nature. Someone else may think: wow, those waves *bounce* inside the earth? I didn't realize that.

Why is such information important? I think it's important because it may give that person a clue, how we happen to know so much about the inner planet. It's because the shock waves from earthquakes do bounce and refract! Thus, the inner Earth is subject to mathematical analysis, and can be effectively *observed*.

This is an encyclopedia, not a dictionary, after all. :-) You may not be too interested in some of the information given - (yawn, where did that video game control get to?) - but someone else may find it quite interesting.  That is the nature of the human beast.  I realize I'm sounding a bit 'Hemmingway' here, but...one man's milk is another man's poison. Law of human nature! In fact: a lot more could be said about the subject of P and S than I said.

Like: what if you reverse them, and make them S and P? But I didn't want to wear out my keyboard.

The 'social purpose' of any encyclopedia is - of course - to inform, and enlighten, and hopefully do it well, in a way that it's enjoyable to read, and maybe even entertaining. Why? So people will want to read, at a time when they are - in great numbers - forgotting how to. When 'R U 2?' came along, I was shocked, frankly! For a surprising number of people, that's standard English now! Shudder. The chinks speak better English than that! Sorry. Chinese. We're all becoming 'PC' these days too, tragically. As well as only partly literate. The lucky ones. I think Wikipedia admirably succeeds in its goal, which I personally believe is: turning back the tide on the illiterates, the semi-literates and the people what don't read so good. It's becoming a serious source of information. Impressive. Just from a lot of contributions, by a myriad unpaid people. Imagine that: a communist system. See: communism. (And I offer also a prayer: may the cyber-vandals who have done naughty in Wiki, and you know who you are, all die, most painfully, preferably by...being sanded, with an electric power sander...slowly...down to nothing. Beat that for a curse on the evil ones.  To quote George Bush.  Who I note: can't read too well.  See?  Even politics thrown into this reply!)

Those who can't read, or who prefer *short* paragraphs, of ideally one or two sentences...should not mess with encyclopedias, in my opinion. No. Because: encyclopedias can require some patience. (Also an old-fashioned virtue, very uncommon these days, I've noticed.)

I would say: don't be too eager to slice things up, too much. Much of what is there has *already* been sliced - rather tragically (sniff) - out of Seismology. Just to shake things up, I guess. (A seismic joke.) At least the information was not moved to mythology. Notice: just to annoy you: a too long, comprehensive reply. :-) Stellar-TO 00:19, 21 April 2006 (UTC)

Question about the sentence in the opening paragraph: "Seismic waves are also continually excited by the pounding of ocean waves and the wind." I thought it would be seismic waves that initiate waves (tsunamis) not the other way around. Is this supposed to be there? If so, maybe it should be explained later in the article. I don't want to delete it unless it should be deleted.


 * This is correct - commonly referred to as microseismicity. For example, every time a wave breaks on the shore, the impact sets up waves which you can see on seismograms. It is clearly visible in a comparison of seismic records from stations on islands, as compared to those in the middle of the continents. And don't get me started on stations near motorways... These seismic waves are not large, but they are detectable. J chaloner 22:47, 14 February 2007 (UTC)

Rayleigh waves
"In any case, waves of the reported amplitude, wavelength, and velocity of the "visible waves" have never been recorded instrumentally." What about the Goodyear blimp during the '89 World Series earthquake in Loma Prieta, near San Francisco? It demonstrated, for the first time, that the air column moved with the ground. Well, based on how the air moved (proved by cameras and the blimps instruments), I think it's safe to say that the ground moved in this fashion. Should I change the article to reflect this or does someone else have more information on this? Banaticus (talk) 09:37, 4 August 2008 (UTC)camila & mr negron 4 ever 2getherx3

I lived on the island of Espiritu Santo in Vanuatu for 4 years in the early 1990s. We lived opposite a football field which was to the south of us. We had a number of earthquakes during my time there, which invariably came from that direction. The first indication that you were going to experience a "shake shake" was a rumbling sound that could be heard coming from the direction of the quake. On a number of occasions, I rushed outside to look at the coming quake. Before it reached me, I could see the flat surface of the football field rippling. The coconut palms in the distance could also be seen swaying wildly sideways as well as up and down. Then I felt the quake underfoot. I believe this verifies the claim made in the article that the Rayleigh waves are visible and not an optical illusion. The quake had not yet reached where I was standing and so the ripple effect cannot be explained by the process described in the article. —Preceding unsigned comment added by Erik Hoekstra (talk • contribs) 03:05, 15 January 2010 (UTC)

Love waves
I noticed the section explaining love waves describes them as being both faster than Reyleigh waves, but slowest as well. I for one don't know which statement is true. I would like to see someone who does know the answer to edit the article, then delete this portion of the discussion. A M Leyva (talk) 07:27, 21 July 2010 (UTC)

New Figures
I was searching around the web for a better example of figures on the waves. I stumbuled across this website that has a .gif of all 4 of the waves that you may want to consider adding to your page.

http://web.ua.es/en/urs/disclosure/seismic-wave-propagation.html

earthquakes
What is the difference between a seismic wave and an earthquake? Cesiumfrog (talk) 07:00, 10 January 2014 (UTC)

OTL: Pc & Sc Wave Speeds and Differentials
Something seems very amiss here regarding P and S wave speeds. On one hand, it is stated:

"the distance from a location to the origin of a seismic wave less than 200 km away is to take the difference in arrival time of the P wave and the S wave in seconds and multiply by 8 kilometers per second."

On the link Earthquake location, there are Gardner's relation and http://www.geo.mtu.edu/UPSeis/locating.html. The later has a nomogram showing also about 8 km/s for the speed difference between P and S waves.

At first appraisal, "S-waves are slower than P-waves, and speeds are typically around 60% of that of P-waves in any given material", so that suggests that P waves travel at 8 * (1-.6) = 20 km/s.

On the other hand, looking at https://www.engineeringtoolbox.com/sound-speed-solids-d_713.html, there is no terrestrial material supporting that sound velocity.

Using Gardner's relation, and re-arranging the formula to V = (rho/.31)**4 with crustal rho as 2.8* yields 6655 m/s for P wave speeds.


 * https://www.rsc.org/Education/Teachers/Resources/jesei/waves/home.htm

This brings forth more queries what other sources state:

https://wiki.seg.org/wiki/Velocities_in_limestone_and_sandstone

https://link.springer.com/article/10.1007/BF02650942

https://earthquake.usgs.gov/data/crust/nam.php

https://earthquake.usgs.gov/data/crust/sam.php

https://escweb.wr.usgs.gov/share/mooney/2002_BSSA_NASeisStruc.pdf

Pc (continental) (km/sec) 6.287

Sc (continental) (km/sec) 3.650

So, maybe I am OTL, but I have no idea how the 8 km/s difference between P and S waves came about.

thanks, Baden — Preceding unsigned comment added by 200.68.142.31 (talk) 00:58, 25 June 2020 (UTC)


 * Okay, I figured out I was OTL! I made a simple reciprocal error.  S=v*t [S=position, v=velocity, t=time], so dv=dS/dt [dS~(6.5-3.3), dt~(1-0.6)].  This yields 8 km/s.


 * 200.68.142.31 (talk) 17:14, 25 June 2020 (UTC) Baden K.