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Author Topic: Why Do Seismic Waves Travel Faster North To South than East to West  (Read 3659 times)

Offline neilep

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Dearest peeps Of klevur knowing stuff !

As a sheepy I of course know everything there is to know about seismic waves !!

Look here I am examining the planet in a seismic kind of way !


Me Just moments Ago (picture is to scale !!)

Can ewe help me with the one thing I have yet to know about seismic waves...


Why Do Seismic Waves Travel Faster North To South than East to West ?


ewe see, I just do not know !!...and I want to know cos knowing about stuff is kewl innit ?



If ewe help me I will wave at ewe from a great distance !!



Neil

Seismic waves are full of fun
Enjoy a curry and wave's come out your bum !


chortle chortle ...fnarrr !!






 

Offline Pecos_Bill

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Using the search string, "Do Seismic Waves Travel Faster North To South than East to West ?" on google yields two pages which lack any assertion of the sort. May I ask what source "ewe" got that from?

Perhaps you are confused because S-wave velocity thru rocks is different than it is through water.(1.)

But if that is not the case, I think that we, in the interests of suffering humanity should avoid uttering obvious twaddle so as not to cause a flock of the gullible to go stampeding about the creation like a flock of sheep -- because they saw it in the naked scientist instead of "Uncle Willy's joke bag"

PS: Your map location shows that you are somewhere on the Arabian peninsula. I hope that you are wearing your hat when you go out in the noonday sun.



(1.) http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm
« Last Edit: 29/07/2015 19:41:35 by Pecos_Bill »
 

Offline chris

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Neil! Good to see you back!

I don't know the answer to this question, but my guess would be that the planet composition is relatively symmetrical on the inside and so there shouldn't be a massive difference for wave transmission; that said, there is clearly some sort of asymmetry that generates the Earth's magnetic field with the polarity that it does, but whether that would have an influence, I am uncertain.

Chris
 

Offline neilep

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Using the search string, "Do Seismic Waves Travel Faster North To South than East to West ?" on google yields two pages which lack any assertion of the sort. May I ask what source "ewe" got that from?

Perhaps you are confused because S-wave velocity thru rocks is different than it is through water.(1.)

But if that is not the case, I think that we, in the interests of suffering humanity should avoid uttering obvious twaddle so as not to cause a flock of the gullible to go stampeding about the creation like a flock of sheep -- because they saw it in the naked scientist instead of "Uncle Willy's joke bag"

PS: Your map location shows that you are somewhere on the Arabian peninsula. I hope that you are wearing your hat when you go out in the noonday sun.



(1.) http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm

LOL...thank ewe Pecos_Bill !...I must have mastered the art of uttering twaddle without even realising it.

I did view the conundrum on a BBC program about  Earthquakes. Unfortunately I can not find the referenced program and suspect it's no longer available for viewing !...what a poo !!
 

Offline neilep

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Neil! Good to see you back!

I don't know the answer to this question, but my guess would be that the planet composition is relatively symmetrical on the inside and so there shouldn't be a massive difference for wave transmission; that said, there is clearly some sort of asymmetry that generates the Earth's magnetic field with the polarity that it does, but whether that would have an influence, I am uncertain.

Chris

Thanks for the kind welcome back Doc,

Well, Im convinced !..lol....as mentioned in my earlier reply this was cited in a BBC program and I just made a mental note in my head about it....grrrr !!..I should have been more pedantic in my analism !! (new word !)

Thanks for your response.

I wonder if the spin of the planet might have anything to do with it ?
 

Offline evan_au

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There is a suggestion that Earth's inner core may be rotating slowly relative to the Earth's surface, by perhaps 1 per year. If so, this could contribute to Earth's magnetic field, as differential rotation is a contributing factor in laboratory experiments on geomagnetism.

This rotation was detected because there is an East-West asymmetry in the speed of seismic waves through the Earth's inner core.

See, for example: http://arxiv.org/abs/1111.1121

PS: Since this region of the inner core is thought to experience a gentle rain of iron crystals, I assume that this is no place for ewe...
 

Offline neilep

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There is a suggestion that Earth's inner core may be rotating slowly relative to the Earth's surface, by perhaps 1 per year. If so, this could contribute to Earth's magnetic field, as differential rotation is a contributing factor in laboratory experiments on geomagnetism.

This rotation was detected because there is an East-West asymmetry in the speed of seismic waves through the Earth's inner core.

See, for example: http://arxiv.org/abs/1111.1121

PS: Since this region of the inner core is thought to experience a gentle rain of iron crystals, I assume that this is no place for ewe...


yayyy !!....thank ewe evan_au for this ! That is very interesting.

 I'd have no issues at the inner core of course because I have sheepy magic to protect me !
 

Offline alancalverd

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Are you sure you aren't confusing longitudinal (compression, primary, P) waves with "north-south" waves?

They certainly do travel about twice the speed of transverse (shear, secondary, S) seismic waves but "longitude" isn't related to geographical divisions of the planet, it just means that the particle motion is in the same direction as the propagation velocity of the wave.
 

Offline Pecos_Bill

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I have lived most of my life in California and I know from the two different types of seismic waves, believe you me.

During the Loma Prieta quake that hit the bay area in 1989, I was 40 miles away from the epicenter at work in the Santa Cruz public health clinic. The P and S waves arrived together and made me first think that the building had been hit by a truck  -- a BIG truck. It was a sharp shock that lasted too long to be a truck accident.

The Napa quake was distant enough that I only felt the slower S waves. I was watching an online girlie show when it suddenly seemed that my chair was close on a lee shore in a moderate, non-breaking  sea..
 

Offline neilep

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I'm very interested in the girly show ! did they make seismic waves too ?
 

Offline Pecos_Bill

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As the science forum is frequently visited by the obviously weak-minded, the rest is silence.

It is a well known fact that all true scientists possess strong moral fiber.
 

Offline alancalverd

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That's a new ewephemism!
 

Offline evan_au

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Are you sure you aren't confusing longitudinal (compression, primary, P) waves with.. transverse (shear, secondary, S) seismic waves?

Earth's liquid outer core blocks the S waves, but P waves still pass through.

S waves can propagate through the solid inner core, but can't get out through the surrounding liquid as S waves, but there are apparently mechanisms that transfer some energy between P waves & S waves at the boundary. 
 

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