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  1. #1
    rider of small bicycles geneman's Avatar
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    I'm confused about this Tsunami

    I watched a news special tonight covering the tragic events surrounding the Tsunami. What confuses me is the location of the devistation. Specifically, several towns severely damaged and highlighted on the show were on the "backside" of the island relative to the wave trajectory. I assumed (obviously incorrectly) that damage would require a direct hit by the waves, akin to how wind effects the windward but not the leeward side of an island.

    Why was I wrong?

    -mark

  2. #2
    Guest
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    Start with this link:

    http://neic.usgs.gov/neis/bulletin/neic_slav_ts.html

    If you check other links on that site, it goes into more detail.

    Koffee

  3. #3
    Direct Hit Not Required BlastRadius's Avatar
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    Waves bounce off land masses too. Imagine the water in the ocean is like water in bowl. Slosh it one direction and water will get spilled on the opposite side too.

    [edit]
    The sloshed water may or may not have contributed to the original destruction though.

  4. #4
    deep fried goodness harlot's Avatar
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    Remember that this earthquake didn't drop from above like a rock in a pond, it emanated from the earth's plates below. Its energy wasn't isolated to that one spot on the west side of Sumatra, it shook the whole plate below the region which is why the waters on the east side of Sumatra were equally effected.

    The wave energy generated from this earthquake has traveled almost all over the world, from South America to the US. This bulletin is from NOAA's Pacific Tsunami Warning Center:

    SOME ENERGY FROM YESTERDAYS TSUNAMI IN THE INDIAN OCEAN HAS
    LEAKED INTO THE PACIFIC BASIN... PROBABLY FROM SOUTH OF THE
    AUSTRALIAN CONTINENT. THIS ENERGY HAS PRODUCED MINOR
    SEA LEVEL FLUCTUATIONS AT MANY PLACES IN THE PACIFIC. FOR
    EXAMPLE...

    50 CM CREST-TO-TROUGH AT CALLAO CHILE
    19 CM CREST-TO-TROUGH AT IQUIQUE CHILE
    13 CM CREST-TO-TROUGH AT PAGO PAGO AMERICAN SAMOA
    11 CM CREST-TO-TROUGH AT SUVA FIJI
    50 CM CREST-TO-TROUGH AT WAITANGI CHATHAM IS NEW ZEALAND
    65 CM CREST-TO-TROUGH AT JACKSON BAY NEW ZEALAND
    18 CM CREST-TO-TROUGH AT PORT VILA VANUATU
    06 CM CREST-TO-TROUGH AT HILO HAWAII USA
    22 CM CREST-TO-TROUGH AT SAN DIEGO CALIFORNIA USA

    THIS IS TO ADVISE THAT SMALL SEA LEVEL CHANGES COULD CONTINUE
    TO BE OBSERVED ACROSS THE PACIFIC OVER THE NEXT DAY OR TWO
    UNTIL ALL ENERGY FROM THIS EVENT IS EVENTUALLY DISSIPATED.

  5. #5
    rider of small bicycles geneman's Avatar
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    Thanks for the replies, but I'm still confused. Here's why ...
    look at the map below. The star indicates the site of the quake. The wave flow away from the star was essentially East/West along a 100Km front. The town of Colombo in Sri Lanka was decimated yet it out of the immediate path of the wave. How can this be?



    ... and Harlot, I'm not ignoring your explanation, I just find it hard to believe that the vibrational force 1000 miles away on the West side of Sri Lanka was sufficient to create a new wave with such destructive potential.

    -mark

  6. #6
    deep fried goodness harlot's Avatar
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    You're right, the earthquake would not have created a new wave on the west side of Sri Lanka. I was giving an explaination for how it hit Malaysia. As for Colombo, I'd say the waves that emanated from the epicenter wrapped around the south end of Sri Lanka. Colombo is far enough southwest that the wrapping waves could still impact that city as a southern swell. There's not much of a continental shelf to slow down those waves so when they hit the mass of Sri Lanka they rise up pretty large and hard.

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    Quote Originally Posted by geneman
    The town of Colombo in Sri Lanka was decimated yet it out of the immediate path of the wave. How can this be?
    I haven't seen details on Sri Lanka's damage but it could've been damaged by simple sea level rise rather than a big wave. If Colombo is predominately at sea level and the surrounding ocean bed is shallow then a low amplitude wave can still cause damage.

    For example, where I live is a very similar earthquake zone to this recent event. My town is protected from significant wave impacts due to geography but in a similar large earthquake we will still experience an estimated (according the the news broadcast last night) 3m sea level increase due to all the water energy coming into this area.

  8. #8
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by geneman
    Thanks for the replies, but I'm still confused. Here's why ...
    look at the map below. The star indicates the site of the quake. The wave flow away from the star was essentially East/West along a 100Km front. The town of Colombo in Sri Lanka was decimated yet it out of the immediate path of the wave. How can this be?



    ... and Harlot, I'm not ignoring your explanation, I just find it hard to believe that the vibrational force 1000 miles away on the West side of Sri Lanka was sufficient to create a new wave with such destructive potential.

    -mark

    Think of the island of Sri Lanka as a ship. The "bow" or eastern side of the island splits the wave and the wave will move down the north and south ends of the island. As soon as they get to the "stern" of the ship or western side of the island they will recombine (in this case with less energy) and swirl around the island before dissipating completely. I would suspect that the devistation on the west side of the island, while still bad, wouldn't be as great as on the east side.

    Stuart Black

  9. #9
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    Quote Originally Posted by cyccommute
    Think of the island of Sri Lanka as a ship. The "bow" or eastern side of the island splits the wave and the wave will move down the north and south ends of the island.
    Sort of shows it in this animation:

    http://www.pmel.noaa.gov/~tsunami/sumatra/indo2004.mov

  10. #10
    contrarian lala's Avatar
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    The above is a good illustration.
    Higher ground for the apocalypse!

  11. #11
    don d.
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    Actually, there were two major quakes. The first, originally measured at 8.9 and located at the star on your map, and a second, originally measured at 7.3 and located very close to Nicobar Island on your map, but not shown. If you notice the location of Nicobar, the 7.3 quake could very well have caused a tsunami along the eastern border of the penninsula you mention.

    There were another ~20 quakes along that fault in a 48 hour period following the original 8.9. All of the subsequent quakes were greater than 5 on the Richter scale, quite large in other words.

  12. #12
    Senior Member LordOpie's Avatar
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    ask the people who caused this quake... http://www.google.com/search?hl=en&c...quakes&spell=1

  13. #13
    Senior Member Bontrager's Avatar
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    You also have to consider that there isn't just 1 wave in a Tsunami..
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  14. #14
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    Quote Originally Posted by LordOpie
    ask the people who caused this quake... http://www.google.com/search?hl=en&c...quakes&spell=1
    Thanks for this website. I had no idea this existed.

  15. #15
    Senior Member Bontrager's Avatar
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    Quote Originally Posted by scottogo
    Thanks for this website. I had no idea this existed.
    google????
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  16. #16
    Senior Member LordOpie's Avatar
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    yeah, I can't tell if scott was being sarcastic or if he was refering to scalar weapons.

  17. #17
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    Quote Originally Posted by LordOpie
    yeah, I can't tell if scott was being sarcastic or if he was refering to scalar weapons.
    Well, the weapons. I think the military was messing around with sonar waves in the ocean and that thay have developed a sonar cannon but scalar is news to me.

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