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M 7.5 Indonesia (2018-09-28)

  1. Sep 28, 2018 #1

    davenn

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  2. jcsd
  3. Sep 28, 2018 #2

    davenn

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    from my recorder just before it started over writing the signal …

    180928  UT M7.5 Indonesia zhi.gif


    There were M4.8, 4.7 and 6.1 foreshocks prior to the main M7.5 main shock
    since then there have been M5.8, 5.7, 5.8, 5.4, 5.1, 5.1 aftershocks

    Map of the area …

    180928  UT M6.1, 7.5 and aftershocks Indonesia.jpg


    Dave
     
  4. Sep 28, 2018 #3

    fresh_42

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    Oops, that sounds serious. You already trained me to automatically first ask: Depth? Thank you, Mr. Pavlov, Sir!
     
  5. Sep 28, 2018 #4

    Bystander

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    Borneo?
     
  6. Sep 28, 2018 #5

    Astronuc

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    Region is Sulawesi Tengah (Central Sulawesi). Borneo or Kalimantan is west across Makassar Strait.

    Looking at USGS site, all preceding and subsequent quakes are shallow (10 km), except for M 6.1 - 55km NNW of Palu, Indonesia.
     
  7. Sep 29, 2018 #6
  8. Sep 29, 2018 #7

    davenn

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    that will teach you for not following me :wink: :-p


    As Astronuc said, no.

    That is Borneo that you can partly see in the upper left of the map

    And this event has produced a 2 metre tsunami that have caused further damage.






    Dave
     
  9. Sep 29, 2018 #8

    Astronuc

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    I read this morning that there were tsunami waves of up to 3 meters in Palu and up to 6 m in some places. Perhaps the initial waves were 2 m and subsequent runup was up to 6 m?

    Death toll is at least 400.

    The 7.5 mag earthquake was inland. So what is this earthquake that caused the tsunami, since it was undersea?
    https://earthquake.usgs.gov/earthquakes/eventpage/us1000h3t2#executive
    M 5.2 - 106km NNW of Palu, Indonesia
    2018-09-28 14:26:00 UTC
    Location 0.022°N 119.576°E, Depth 10.0 km

    Or was the 7.5 mag earthquake large enough to cause seafloor displacement?

    The 7.5 mag and related earthquakes occurred in the Palu-Koro fault zone.
    http://temblor.net/earthquake-insig...gering-a-tsunami-and-likely-more-shocks-7797/

    Seismic and Tsunmai Hazard Potential in Sulawesi Island, Indonesia
    https://ir.lib.hiroshima-u.ac.jp/files/public/3/31339/20141016181157824412/JIDC_17-1_17.pdf
     
    Last edited: Sep 29, 2018
  10. Sep 29, 2018 #9

    davenn

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    I tend to agree, specially when I watched the video(s) in the links I posted. It appeared that there was a smaller initial wave,
    that can be seen washing through the street and building by the seashore and the larger second wave in the background.
    It was then followed by that much larger wave that hit with a lot of force completely covering those buildings on the shoreline
    and being a considerable way up that large street sign on the right side of the video which is much higher than the buildings.

    It is very hard to estimate heights of waves when videoed from an angle looking down on them

    I strongly doubt a 5.2 could produce a tsunami, specially one of that size. I have never seen such reported in the past.

    Tho they show the location of the 7.5 as being on land, remember there is a reasonable error circle around that location
    and the fault that it occurred on is offshore, so seafloor displacement is likely.

    Tho the fault is noted as being primarily strike-slip, it obviously does have an oblique slip component ... see the "beachball" moment tensor solution

    upload_2018-9-30_11-41-43.png


    That solution allows for a vertical offset of the seafloor.



    Excellent article …. it amazes me how fast they can produce indepth info for events.
    And it was good to see the offshore fault location

    (cropped to fit here)

    upload_2018-9-30_11-48-40.png



    Dave
     
  11. Sep 30, 2018 #10
  12. Sep 30, 2018 #11

    davenn

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    OK with a bit of searching, I have discovered where that video of the tsunami was taken from. It was from right at the head of that long narrow bay.
    This leads to the possibility of wave amplification as it travels up the bay.

    some severely reduced in size pic's from road level view.

    1) aerial view of the immediate area

    180928 Palu city aerial view.JPG


    2) the carpark spiral ramp from where the video was done . The Mosque can be seen in behind the ramp. It was severely damaged in the quake shaking.
    To the left side of the image is a red mast/pole, just past the street lamp pole ( the unfinished mast is where there is now a large black sign with red writing
    on it ( obviously not finished when Google went through here with their street cameras)
    The videographer was standing with the other people at that narrower ( in height) level, level with the word "SIMPLY"

    180928 Tsunami filming location Palu, Sulawesi1sm.jpg


    3) looking further to the left ( west)

    180928 Tsunami filming location Palu, Sulawesi2sm.jpg


    4) and further again to the left ….

    180928 Tsunami filming location Palu, Sulawesi3sm.jpg


    go to the location in google earth and go into street view for a larger sized image ....
    Lat -0.883346 Long 119.843607

    The first thing that becomes very apparent is the changes of height from beach level to the upper road/bottom of car ramp level.
    I found one spot where there was a clear view of the sea between buildings and there would appear to be approx. one to two metres
    between sea level and those shoreline building floor level. The building floor level is just a little below road level

    Now note from the video, the wave came right over the tops of those shoreline buildings and to around half way up that that large signage
    pole (red on GE, painted white in the video). This infers a wave height of at least 4 metres and possibly more at this location.


    Dave
     
    Last edited: Sep 30, 2018
  13. Sep 30, 2018 #12
    At least 800 confirmed dead in city, sadly thrice more expected, but no signs of life in big town further along coast.

    Looks bad...
    :-((
     
  14. Sep 30, 2018 #13

    davenn

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    yeah, very bad and sad :frown:
     
  15. Sep 30, 2018 #14
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