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New online Seismograph

Discussion in 'Off-Topic Members Lounge' started by davenn, Oct 18, 2012.

  1. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi gang

    something I have been wanting to do for some years is to get real time seismograms from my recorder online.
    Finally achieved that last weekend. I use a program called Snagit which runs in the background and every 5 minutes does a screen capture and ftp's it to my www site for anyone to log in and view

    Quake recorder

    there's an event that happened about an hour ago
    a M5.7 far south of Tasmania, Australia visible on the drum at the moment

    its ~ 2346 km SSW of my home/recorder here in Sydney, Australia

    cheers
    Dave
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Nice work, Dave.

    But: how do I read the chart? The vertical axis is time, as it has time stamps. but what is the horizontal axis showing? Or do I have to continue from the right to the left of the next line below as in reading a text?

    Also you might want to space the lines a bit wider so the peaks do not so easily overlap.


    Harald
     
  3. davenn

    davenn Moderator

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    Sep 5, 2009
    OK ... you can see time (in UTC) down the left side incrementing at 30 minute intervals
    ie. each line across the screen is 30 minutes. It just labels every 4th line to save text congestion down the side. If you sit on the page for a while and do periodic refreshes you will see the trace moving left to right across the screen.
    So X and Y axis are both showing time ;) just to fool you. We are not worried about physically measuring amplitude on this screen.
    From within the probram I can pull out an even from any time since the data recorder started --- ie. in this case over the last year and a bit. I can pull out that event and look at it in the analysis software and do distance and magnitude calcs and also add in the quake information for the USGS (United States Geological Survey) or other institution.
    eg ... event origin date/time - Lat/Long depth etc

    they are going to overlap anyway on the bigger quakes or big bursts of manmade noise many lines get overlapped. Thats not a real issue, its pretty much similar to any of the institution ones and other fellow amateur seismologists


    Dave
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Thanks, Dave.
    I understand that. On old mechanical seismographs this was certainly due to mechanical limitations (if you had more than one trace).
    How about coloring every second line in a different color? Even it has been traditionally as you describe, I see no need to stick to the tradition if a fix can make life easier.


    But then again ai'm not into seismology. Maybe it is not necessary.

    Harald
     
  5. davenn

    davenn Moderator

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    Sep 5, 2009
    OK here's an image of the event after its been put into the analysis program
    and have done some FFT lowpass 6 pole filtering with a cutoff at 5Hz to cut out a lot of the manmade and other higher freq noise

    [​IMG]


    now for some other info....

    There are 4 wave arrivals nother on the seismogram

    P = The P wave is the fastest travelling, ~ 7 - 8km/sec. It is a compressional wave like a sound wave. Their frequency avg's around 1 - 5 Hz, give or take a little

    S = S wave it travels a bit slower ~ 5 - 6 km/sec. It is a shear wave ... ground motion is perpendicular to the direction of propagation. Their frequency avg's around .1 - 1Hz, give or take a little

    The LQ and LR are the surface waves, they dont penetrate into the earth to any great distance, a few 10's or so of km. They are the slowest travelling at ~ 3 - 4 km/sec
    and are complex styles of shear waves.
    LQ = Love waves, LR = Rayleigh waves
    It is the surface waves that do the damage to buildings and other structures. Their very low frequency from ~ 10 to ~ 200 seconds/cycle. are, along with various ground types allow structures vibrate at their resonant freqs and demolish themselves.

    ( I will add to that ... there is also the initial hi acceleration pulse that can do initial damage to weaker structures.)

    OK there's seismology 101

    cheers
    Dave
     

    Attached Files:

  6. davenn

    davenn Moderator

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    Sep 5, 2009
    we leave the different colours for showing additional channels.
    one my system is fully operational there will be 5 channels. At the moment there is 1 within hopefully the next 2 months I will finally find time to get the next 3 sensors online then some time in the future there will be another long period sensor like I have running at present. It will be orientated perpendicular to the current one.
    The current one has its pendulum boom orientated east-west so its sensitive to quakes from the north and south. the next one will have the boom orientated north-south so it will pick up the events to the east and west better.
    The current sensor doesnt do well recording events perpendicular to its orientation.

    Dave
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Thanks for the explanation. Very interesting.
    Could you identify this event? Is it a true seismic event or possibly man-made?
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009
    Oh I meant to add, even when there are 4 or 5 channels being recorded, I will only at most display 2 of them, probably one short period and one long period sensor. and then I will have to cut back on the trace hours visible on the screen.

    Currently, it displays ~ 36 hours from the top to the bottom of the screen.... when the trace finally gets to the lower right corner the screen clears, it is set to display the last 15 trace lines and then continue on from there

    Have a look at my seismo page to see the sensor I built and the commercial tri axis sensor set etc.

    D
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    That's very cool Dave
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009
    manmade events wont cause traces this big... well not these days anyway
    back in the 50's - 70's era of underground nuclear testing, events of M4.5 - 5.5 were easily produced. The New Zealand Institution for recording quakes kept a close eye on Muroroa Atoll in the south Pacific with the French nuclear testing

    There was very little difference in the seismograms. The big giveaway was that because the blast is a point source there is a pretty much equal P ( compressional) wave radiating out in all directions.
    Natural quakes are not point sources, rather they are on a faultline that has some length to it. and from that we can identify the orientation of the faultline that ruptured

    we look at the first motions of the arrival of the P wave at various recorders spread around the world, look at this page of mine for a bit of an explanation NOTE graphic image B that has a fault orientated NE SW note the arrows on each side of the fault and the C compressional quadrants and the D dilational quadrants

    Dave
     
  11. davenn

    davenn Moderator

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    Sep 5, 2009
    Thanks Steve

    This is really one of my major passions in life ( yeah astronomy is another ;) )

    it can be difficult to get me off my soap box once I get started
    but if some one is willing to listen, I will waffle and hopefully teach a little for hours

    D
     
  12. wingnut

    wingnut

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    Aug 9, 2012
    Davenn

    Must be so satisfying to achieve this long term goal.

    You left the tectonic plates of New Zealand for the quieter Australia.
    I have heard of storm chasers but are there quake chasers? :)

    Maybe you can tell be if earthquakes are on the increase or not.

    Years ago I remember a site which had a map of the world and recorded every earthquake with a symbol. Have you seen this site?
     
  13. davenn

    davenn Moderator

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    Sep 5, 2009
    yeah go figure haha I used to record so many New Zealand events
    Yup my wife I also stormchase .. in Aussie and the USA

    there is no obvious trend to say that quake numbers are increasing.
    over the last ~ 120 years of world data collecting by various institutions ... particularly the USGS .... shows that the number of events is pretty stable

    yearly averages are 1 x M8 + ; 18 x M7.0 - 7.9 ; 100 x M6.0 - 6.9 ; 1000 x M5.0 - 5.9
    1000's of M4.0 - 4.9 etc etc

    some years like this one (2012) we get a couple of M8+ events, other years none, it all averages out to ~ 1 / year


    The USGS produce maps with quake locations over various periods of time

    Ohhh BTW you can just call me Dave not davenn ;) the nn are the first and last letters of my surname

    cheers
    Dave
     
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