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Tsunami caused by the earthquake.

  1. Dec 30, 2004 #1
    I was reading in the newspaper and saw that it said that there was first an initial tidal wave, then the water receded for 10 minutes, then the big wave came crashing ashore. I was just trying to think on why the water would recede for so long, being 10 minutes. When the earthquake takes place how exactly does it effect the water? Does it first give an outward push causing the small wave then cave back in causing the water to recede and all of the water that receded rush back outward?
  2. jcsd
  3. Dec 30, 2004 #2
    I actually thought this through in the first instance of when I seen the first report, early (uk) boxing day morning. The BBC report showed a graphic image of Tsunami, shoreline's close to the epicentre would experience a rapid tidal receeding effect.

    This was caused by the ocean 'welling' upwards over the earthquake area, enough to cause closeby tides to receed, but coastlines that were far away had no receeding effect.

    At least that is how I read the early reports?
  4. Jan 1, 2005 #3
    Anyone can answer this? Or maybe send some sites on how earthquakes form tsunamis?
  5. Jan 1, 2005 #4


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    Wow, I heard that on the news, but thought nothing of it, that's REALLY interesting... ohh I just thought of an explination:
    ( http://en.wikipedia.org/wiki/Image:2004_Indonesia_Tsunami.gif )
    Many waves of varying heights were produced by the 9.0 earthquake, as shown in the computer generation taken from NOAA.
  6. Jan 1, 2005 #5


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    Staff: Mentor

    That "welling up" is the tsunami itself - and since the tsunami is just like any other wave, it has a trough like any other wave - and both propagate together. Its less noticeable (and much, much smaller, of course) but every ocean wave works exacly the same way. When you're at the beach and see the water pulled toward a coming wave, it really is being pulled toward the coming wave - its not just that the previous wave is receeding.

    Coastlines further away had less of a receeding effet because the tsunami was much smaller further away.
  7. Jan 1, 2005 #6
  8. Jan 1, 2005 #7
    Nice links Tom, thanks.
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