South Pacific Tsunami Caused by Two Earthquakes in One

By Joseph Calamia | August 18, 2010 6:25 pm

Originally scientists believed that one earthquake had set off the deadly tsunami that struck Samoa, American Samoa, and Tonga in September of 2009. But two studies to appear tomorrow in Nature argue that instead of one there were really two earthquakes that took place in rapid succession.


For some scientists, the studies clear up odd behavior that didn’t fit with the originally blamed “normal-fault” earthquake in the Pacific Northwest.

“We knew right off the bat that something was weird about this earthquake,” says geophysicist Eric Geist of the U.S. Geological Survey in Menlo Park, Calif. Geist wasn’t involved in the current studies but has puzzled over the anomalous signs produced by the quake. “This is a very complicated event, and these studies, for me, really helped explain a lot.” [Science News]

John Beaven, lead author of one of the studies, told Nature News the researchers expected the Tongan island to move about three inches to the west as a result of the quake, but GPS showed it had moved nearly a foot east. They also expected the sea bed to drop but instead it rose, a sign of a different kind of “megathrust” quake. A separate study led by Thorne Lay confirmed signs of this alternate type of earthquake from seismic readings.

Though both studies point to two different types of earthquakes, they disagree on which earthquake came first and caused the other. Ronald Burgmann, a geophysicist at the University of California, Berkeley, who was not involved in either study says, overall, they both make a good case:

“As in all good chicken-and-egg mysteries,” he says, “there is merit to both views.” [Nature News]

Related content:
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Image: Mick Finn, GNS Science

  • Kevin

    And global warming will destroy us all too, right? Modern scientists are the same as modern phycologists, filled with BS….

  • Nemesis

    “And global warming will destroy us all too, right? Modern scientists are the same as modern phycologists, filled with BS….”

    I didn’t realize the people who study algae (phycologists) are full of it. Psychologists, on the other hand…

    Do you prefer the works of ancient scientists, sir? Flat earth, geocentric universe, and leaches for curing disease-all good things?

  • MWS

    Good one,Nemesis!

  • Chris the Canadian

    What the heck does Global Warming have to do with this article? Two Geophysicists discussing the event in Samoa last year and coming to the same conclusion, that 2 earthquakes occurred to cause the giant Tsunami rather than one after reasearching and looking at the results is actually GOOD SCIENCE!!! They followed the method by looking at the event, evaluating the data, taking into consideration the variables, comparing the data to the hypothesis of one earthquake causing the tsunami, and concluding that 1 earthquake could not have been the cause of the tsunami and shift in the island 1 foot to the east.

    If anything, these geophysicists did an excellent job and should be congratulated, not ridiculed.

  • Albert Bakker

    Sometimes ridicule is preferable to congratulation, much depending on who you receive it from. While being ridiculed is never a great delight, hardly ever even the cleverest use of wit is sufficient the hide from view it’s hostile intent and this always eases the mind to quickly put it aside. The depressing mood and gnawing distress undesired congratulations are able to instill in a person is however much longer lasting.

  • Justin

    On the subject of Scientists being full of BS:
    If you think that being “incorrect” about something is the same as being “full of BS,” so be it. But let us remember that science is a field where people constantly adapt and bend to evidence that changes perceptions. 100 years ago, we thought our galaxy was the only one. Then Hubble found that many of those lights in the sky that we thought were stars were actually OTHER galaxies. And then we found they were moving away from us. And then we realized if they’re all moving away, they all must have started from the same place, which leads to Big Bang and… well, you get the idea.
    Or how about matter? Greeks thought everything was blocks. Fast forward to the model of the atom with a nucleus of Protons/Neutrons surrounded by electrons. And that was was small as things got… until it wasn’t anymore.
    Scientists are always looking, always uncovering, always adapting and bending. Is that BS? A good scientist will tell you with every discovery he/she learns of how much more he/she DOESN’T know.
    And how about obstinate religious fundamentalists who adhere to the same bogus ideas, no matter how much evidence is shown to the contrary. Who is more full of BS: Those who think they know all and do not adapt, or those who are constantly in pursuit of the truth?


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