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Mysterious Ringing of the Earth

  1. Nov 29, 2018 #1

    jedishrfu

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    A recent Nat Geo article highlights a mysterious ringing of the Earth whose source is localized to the island of Mayotte but whose origin is unknown:

    https://www.nationalgeographic.com/...ake-waves-rippled-around-world-earth-geology/

    @davenn did you see this too?
     
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  3. Nov 29, 2018 #2

    davenn

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    Thanks for that

    I wasn't aware of that one ...... Not sure why the USGS didn't report it, it was reasonable amplitude surface waves. I will have to check my data and see if I recorded anything :smile:
    There were around 4 other events in that same area during November that were reported, the largest a M5.0

    this is the unknown event as recorded in

    181111 seismic segnal from off shore E.Africa.jpg

    basically a set of low frequency surface waves with a lack of P and S waves ... this isn't uncommon, I see that often on my recordings
    where at a distance from the recorder, the higher frequency P and S waves have been heavily attenuated

    that statement is VERY misleading ..... shows a total misunderstanding of quakes shown on seismograms. I will have to check my data and see if I recorded anything :smile:
    Any reasonable quake will have the signal going on for some time. and of course, if you are not close to the event, you wont "feel it"

    a little similar from my system, just one I have on my work PC
    could look through records at home and possibly find a better example :wink:

    181122  UT M5.9 Pacific-Antarctic Ridge zhi.jpg


    The P and S waves are very low amplitude but a good surface wave trace .... M5.9 5000+ km from recorder


    edits to fix image and finish text


    Dave
     
  4. Nov 29, 2018 #3

    jedishrfu

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    That's awesome, I feel like I'm now plugged into the Earth's Seismic network. Thanks Dave.
     
  5. Nov 29, 2018 #4

    davenn

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    I was having trouble uploading that second image and you did a post like whilst I was still editing haha

    you can see in that example of mine, even for a moderate event, the surface waves went on for an hour or so, not just a mere 20 minutes
     
  6. Dec 1, 2018 #5

    davenn

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    just had a chance to go back through the data
    WOW ... I got signal from it. Comparing to the arrival time on the New Zealand sensor in Wellington, it makes the timing correct for my station in Sydney, Australia.

    upload_2018-12-1_22-19-18.png


    The time along the bottom is UTC on the 11 Nov 2018


    Dave
     
  7. Dec 1, 2018 #6

    jedishrfu

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    So now the next step is what do you think it is?

    Do you think there’s any connection to it and the Alaska earthquake?

    I figure that may be a stretch to think that but it’s odd that Alaska got hit with such a large one after so many years of relativ quiet.

    I found this article on Mayotte of an earthquake swarm in May. 2018

    https://watchers.news/2018/05/15/ea...-oldest-volcanic-island-in-the-comoros-basin/

    So apparently it’s been known for a lot longer.
     
  8. Dec 1, 2018 #7

    davenn

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    As I commented earlier, it is really strange that the UGSG never reported an event there for that time, but did report the other events.
    This, of course, has led to lots of wild speculation across the net as to what it was ??

    Maybe is it volcanic in origin ? The movement of magma ? tho it doesn't have the appearance of what would usually be termed "harmonic tremor".
    Harmonic tremor tends to be more "even" in amplitude with occasional stronger pulses eg .....

    CHIE_2012-01-20.19.28.utc_.jpg
    4 channels are being recorded here ( 1 colour trace for each channel)
    I personally have never seen volcanic harmonic tremor with a smooth drop off of amplitude, producing a nice "bell" shape as in
    post #2. Harmonic tremor doesn't produce P and S waves as it is a continuous low level fracturing of rock as magma pushes up towards the surface.

    No, definitely not, The Anchorage M7 event was a crustal (crustal = down to ~ 50km depth) tectonic quake. Primarily caused by
    the subduction of the Pacific Plate under Alaska. Tho the subduction region is much deeper, it will always cause faulting/quakes
    at shallower depths, commonly reverse thrust faulting and events. This can be seen in pretty much any subduction zone around
    the world.


    Always good to think about these things. There was a large event south, well offshore a few months back ~ M7.8.
    The last really big even within Alaska was the Mw 7.9 Denali fault quake in 2002. It ruptured over 300km for Faultline.
    I didn't record that one , it was only 2 years after I arrived in Australia from NZ, and didn't have my seismic station set up at that time.
    The largest event in the Alaska region was the 1964, Mw 9.2, event not too many km SE of Anchorage. There would be many
    people living there today and that felt the M7.0 and well remembered the 1964 event and bringing back scary memories.



    Some good info. Yes, there has been quite a number of events since around May 2018. I was reading that in a different article yesterday.

    So it's still the frustration of not knowing the cause of that seismic signal


    Cheers
    Dave

    EDIT - fix typos
     
    Last edited: Dec 1, 2018
  9. Dec 1, 2018 #8

    jedishrfu

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    Thanks Dave. Your commentary always teaches me new things to look at and learn. My usual work involves things around acoustics but I’m more like a software janitor not really understanding the science behind the models we use.

    WRT the USGS it may be that software decides what events are important to report on so these more harmonic tremors are routinely ignored.

    One question I had about your station setup. Is this a personal hobby like ham radio or is this more formal and connected to some university?
     
  10. Dec 2, 2018 #9

    davenn

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    Cheers, I am no expert, but I do seem to be one of the few involved in earth science on these forums. I did most of my BSc in geology
    in New Zealand before coming to Australia almost 19 years ago. I really only had my 3rd year final paper to do and 1st year maths
    papers and I would have completed the degree. But life took a major turn and I moved countries.
    Well, P waves in seismology and acoustics go hand in hand in the way they travel through different mediums and other properties.


    Probably true, but anything significant would be reviewed by the duty seismologist(s) and with something unusual like this
    that was recorded far and wide around the world, it just seems strange that there has been a lack of comments from them.


    It's a very serious personal hobby around 1990. I ran ink on paper around the rotating drum up till I left NZ in Jan. 2000.
    From 1995 or 1996, I was running a digital system after I met up with a bunch of guys in California that started up the PSN (Public Seismic Network),
    http://psn.quake.net/ ....
    It grew to be a worldwide thing and was a mix of professionals from the USGS, running their own systems at home, as well as all us amateurs.

    A link to my online channels ( 5 out of 6 of them and one of 5 currently offline) ....

    http://www.sydneystormcity.com/seismograms.htm

    A link to the page showing my sensors and other info ....

    http://www.sydneystormcity.com/g_phones.htm

    The only affiliations to professional organisations I have these days are

    International Registry of Seismograph Stations

    and my station listing ....
    http://www.isc.ac.uk/cgi-bin/statio...tn_left_lon=&stn_right_lon=&stn_srn=&stn_grn=

    and am a member of the Geological Society of America
    http://www.geosociety.org/GSA/contact.aspx?_zs=MIvNb1&_zl=elOx4

    When I was in NZ and particularly during my years at uni. I was a member of the Geological Society of New Zealand
    now days known as Geoscience Soc. of NZ
    http://www.gsnz.org.nz/information/branches-i-3.html

    Their monthly meetings were always held in the geology dept. at Otago University, so it was really handy. Finish study for that day then attend the meeting



    cheers
    Dave
     
    Last edited: Dec 2, 2018
  11. Dec 2, 2018 #10

    davenn

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    just has a memory flash

    I knew I had seen seismic traces like that in post #2 above somewhere before ......

    Lunar (Moon) quakes and from one of my www pages .....

    http://www.sydneystormcity.com/moonqk.htm

    scroll down the page and there's a bunch of examples
     
  12. Dec 2, 2018 #11

    fresh_42

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    Potsdam hasn't it either: https://geofon.gfz-potsdam.de/eqinfo/list.php?page=7
     
  13. Dec 4, 2018 at 6:17 AM #12
    @davenn Very curious, I wondered if you had the sound file. I would like to hear transposed to audible range maybe in audition or audacity.
    ref->
     
  14. Dec 4, 2018 at 2:27 PM #13

    davenn

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    I have never tried converting the seismic file to a sound file. I am aware of others who have done that in the past,
    tho I am not sure how I would do that ?


    Dave
     
  15. Dec 4, 2018 at 2:30 PM #14

    jedishrfu

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  16. Dec 5, 2018 at 8:05 AM #15
  17. Dec 5, 2018 at 2:55 PM #16

    davenn

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    A great insight into how things are done by the professionals. There are a number of good things in there that the amateur
    can still take into account when building a home station. Particularly when it comes to housing the seismometers. The main
    considerations being thermal and air pressure stability and I personally know the frustrations that can be had with those things.

    I really do need to find time to write an "Insight" article on amateur seismology .... time nor health is not on my side :frown:


    Dave
     
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