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Antipodal seismic focusing after an impact: real or not?

  1. Mar 13, 2016 #1
    Reading about meteorites, I have found this idea of "antipodal earthquakes" or "antipodal vulcanism" after a major impact several times. There seems to be perfectly good papers for and against, together with the usual crankish "information." There also was a thread here about the issue almost 4 years ago.

    My question is simple: is anyone aware of any more recent research for or against this antipodal seismic focusing effect, please? (I haven't been able to find anything.) And... do you think it's plausible or far-fetched, or is the jury still out there?

    Thank you in advance!
     
  2. jcsd
  3. Mar 13, 2016 #2

    jim mcnamara

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    Start with this from 2011. There is a link to the primary paper, which again has papers cited.

    https://www.princeton.edu/main/news/archive/S31/90/32S94/index.xml

    I do not think the topic is dead, just that developing models can be expensive, (IMO) and that grant money is going elsewhere. See also 'Theoretical Global Seismology' by Jeroen Tromp - the lead author of the citation above.

    We have someone here @D H who works, I think, in planetary sciences. He will certainly have better information than I do. It is not my field, and I read for interest - which translates to: "I am far from an expert."
     
  4. Mar 13, 2016 #3
    Yes, that was one of the "perfectly good papers" I was talking about. :wink:

    Certainly! That's a good idea I hadn't thought of, I didn't know about this Theoretical Global Seismology. Thank you very much! :smile:
     
  5. Mar 14, 2016 #4
    Although I'm a layman, I've spent many years researching meteorites and crater impacts in depth, and all I've read fully supports the idea of seismic waves which rebound around the planet's structure, sometimes several times after a major impact or explosion event such as a nuclear test. That's how many impacts and undeclared tests have been detected and revealed, through seismic readings from around the world. Also, it's perfectly possible to pinpoint general locations for the origin by correlating timing and strength of the waves as they are detected at multiple locations. Unfortunately you'll have to take my word for it, because I don't have any websites I can cite for you. Having said that, the Oaklahoma Geological Survey published a now famous list of known and putative nuclear tests based on seismological evidence. Some of the events listed are doubtful as to their provenance - whether nuclear or impact - but it proves that even low yield tests - sub-kiloton range - can be detected worldwide, and many major impacts have potential yield equivalents going into the megaton range or far higher. So, to answer your question simply, yes. There's ample evidence for seismic events after an impact.

    You can find the full OGS test list here:
    http://www.okgeosurvey1.gov/level2/nuke.cat.html [Broken]
     
    Last edited by a moderator: May 7, 2017
  6. Mar 14, 2016 #5
  7. Mar 14, 2016 #6

    davenn

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    but that wasn't the Q
    That effect is well established

    the question by the OP was ....

    Dave
     
  8. Mar 14, 2016 #7

    davenn

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    No, you didn't ... your comments had only to do with detection ... and didn't address the seismic focussing
    The OP wasn't interested in detection

    It's not a quibble
    You plainly answered incorrectly and that doesn't help the OP
    It pays to read OP questions just a little more carefully ... It's a mistake any of us can make :wink::smile:


    Dave
     
  9. Mar 14, 2016 #8

    davenn

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    Hi xpell

    sorry that cadar is off on an incorrect tangent and doesn't want to acknowledge the fact

    Tho I have done lots of study in seismology, your topic is one I know little about
    Yes, there is seismic focussing of the energy, but how strong that is, I'm a bit in the same boat as you without having definitive info one way or another.

    That Princeton article Jim linked to is at least from a reliable source.
    https://www.princeton.edu/main/news/archive/S31/90/32S94/index.xml


    Dave
     
  10. Mar 14, 2016 #9
    Seems being less than 100% accurate in one's replies gets one bitched at and mail-bombed. Had I known that, I'd probably have not bothered to respond in the first place. Xpell, my apologies if there's any confusion and for the ridiculous back-and-forth on your thread.

    Just out of interest, I did a quick Google, and came up with these links. One of them is from 2015, does that count as "recent"?
    https://gsa.confex.com/gsa/2015AM/webprogram/Paper260891.html
    https://www.princeton.edu/main/news/archive/S31/90/32S94/index.xml
    http://dspace.mit.edu/handle/1721.1/69472
    http://www.newgeology.us/presentation35.html
    Those are only the first four hits. I had pages full of relevant links off Google. My search keywords were "seismic focussing impact event". I didn't include "antipodal", but Google found some links anyway. Gotta love the internet.
     
  11. Mar 15, 2016 #10
    The crater in Eastern Antarctica was pretty large & seemed timed to the Siberian Traps, while some feel not enough energy will open vents, local faults where the energy arrives may allow mantle lavas to escape upward in new vents, melting the fault surface as it goes this would create the broad fountains and flood versus the pipes of a volcano and take a while to appear a thought.
     
  12. Mar 21, 2016 #11
    I wrote a patent application in 1999, which used the idea of constructive interference of seismic waves from
    vibroseis trucks. The weathering layer of the ground could act like a waveguide.
    Two or more trucks could identify the modulus of elasticity in the local soil.
    One truck would center on the frequency of the modulus of elasticity, while the other would be just slightly
    off frequency. (sorry if this is a little off, but it's from memory from 17 years ago.)
    The closer to the center frequency, the further the interference pattern was away.
    The phase of the other trucks to truck one determined where on the arc of truck one the interference would occur.
    The frequencies were all in the 10 to 120 hz range, with the "c" being the speed of sound in that type of soil.
    My company, decided it was interesting, but not up their alley, so I published it.
    I did try a few rough experiments at home, but it upset the dogs....A LOT!
    I should have added the purpose of the idea, was to see if sounds waves could be used to clear land mines.
     
    Last edited: Mar 21, 2016
  13. Mar 22, 2016 #12
    Tangentially, a spherical charge inside a spherical space underground was shown in a British experiment to produce no seismic detection, unless very close.
     
  14. Mar 22, 2016 #13

    davenn

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    do you want to elaborate, I don't see what spherical charges have to do with seismic waves or the focussing there of


    Dave
     
  15. Mar 22, 2016 #14
    It was an experiment in seismic detection, seismography used to monitor waves resulting from underground nuclear testing, and natural phenomena. Two people perished in a section of the old mine used in SW England, lack of oxygen. A very large charge was exploded the access once set blocked to maintain the shape of the excavated sphere in rock. The exception to the rules and phenomena established recording underground tests and natural phenomena on another "side" of the Earth that might be antipodal.
     
  16. Mar 22, 2016 #15

    davenn

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    ohhhhhhhhhhhhhh an explosive charge, that wasn't initially obvious from your first post

    I record mining blasts on an almost daily basis, sometimes several a day, from around 6 different mine sites ranging from ~ 100 - 150 km from my location


    what was the definition of very close ?


    cheers
    Dave
     
  17. Mar 23, 2016 #16
    Not all frequencies carry well through the weathering layer,
    depending on the local soil makeup.
    There is also a fairly stiff attenuation, but the wave I am speaking of are good for several hundred meters.
    To get something to carry 12 K miles, would involve a very limited set of frequencies,
    and likely something traveling in the deep rock.
     
  18. Mar 23, 2016 #17
    As I recall less than a km, but it's been awhile, it was on the Internet a number of years ago.
     
  19. Mar 23, 2016 #18

    davenn

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    OK, so they must have been very small detonations
    The open cast mining blasts I observe vary from around 1 to 10 tonnes of amfo. The larger blasts will give an equivalent
    quake magnitude of around ML 2.5. Neither these, nor the much larger nuclear test blasts will result in the size of seismic
    waves suitable for doing antipodal focussing research, as being discussed in this thread, as there just isn't enough seismic
    energy produced. It's the M8 to M9 + events and of course large meteoritic impacts that do produce enough energy.

    Dave
     
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