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Keywords searched: 8 February 2005 Interview with Dr. Hal Mofjeld

  1. How do scientists gather information and detect tsunamis?
  2. Is there more than one way to detect tsunamis?
  3. How does that information help us to create better tsunami warning systems?
  4. Is there anything scientists learned from the Dec 26, 2004 Sumatra tsunami in particular?
  5. Did this last tsunami prove to scientists that current detection and warning systems are effective or not? If not, what are scientists doing now to improve those systems?

  1. How do scientists gather information and detect tsunamis?

    Tsunami scientists gather data from tide gages and do field surveys in areas hit by tsunamis to better understand the behavior of real tsunamis. This information is then used to tune computer models that can be applied to other areas. I'm assuming you refer to the new DART buoys we're developing. These will help make the tsunami warnings faster and more accurate. Right now, the warning centers depend on earthquake data and on tide gage data to assess the danger. The earthquake data tells you how big the earthquake was, and the location of the epicenter.

    If the location is:

    1. in a region that has generated tsunamis in the past -- basically, very seismically active regions of the "Ring of Fire" around the Pacific Rim, where plate tectonics drives the Pacific plate under various continental plates, and
    2. if the earthquake is big enough, i.e., about a magnitude 7 or greater, then it is considered a possible tsunami hazard.

    But the warning center still doesn't know if a tsunami was generated, because it doesn't have a way to measure it, until the tsunami propagates into a nearby harbor and registers on the tide gage.

    That may take a while, and:

    1. it's too late to warn the folks in that particular harbor and
    2. you may have lost a lot of time waiting for the tsunami to register on the tide gage.

    So DART systems are being place close to the potential tsunamigenic zones, offshore in deep water. That way, if a tsunami is generated by the earthquake, you get the measurement right away. Not only that, but you know that it is headed out to sea and you can warn communities across the ocean that a tsunami is heading toward them.

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    Authority: Dr. Hal Mofjeld, NOAA Center for Tsunami Research

  2. Is there more than one way to detect tsunamis?

    Tsunamis are detected and measured by coastal tide gages and by tsunami buoys in the deep ocean. The tide gages measure the tsunami wave directly. In the deep ocean, sensors on the ocean floor detect the pressure signature of tsunami waves as they pass by. Sometimes by chance a satellite that can measure water levels passes over a tsunami and detects it; this was the case during the tsunami in the Indian Ocean.

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    Authority: Dr. Hal Mofjeld, NOAA Center for Tsunami Research

  3. How does that information help us to create better tsunami warning systems?

    For improved tsunami warning systems, the data collected immediately after a tsunami is generated will be used as input into computer models to forecast the heights of the tsunami when it reaches the shore. The data are presently being used to verify that a tsunami has been generated. This is important since sometimes large earthquakes do not generate dangerous tsunamis but other times they do.

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    Authority: Dr. Hal Mofjeld, NOAA Center for Tsunami Research

  4. Is there anything scientists learned from the Dec 26, 2004 Sumatra tsunami in particular?

    Scientists are presently doing field surveys and setting up computer models, with the expectation that much will be learned from this research. Once this work is done, we'll know a lot more about the details of the earthquake and tsunami. The one surprise that the fieldwork has shown so far is that the height of the tsunami at Banda Aceh, Sumatra, was much higher than was expected.

    Authority: Dr. Hal Mofjeld, NOAA Center for Tsunami Research

  5. Did this last tsunami prove to scientists that current detection and warning systems are effective or not? If not, what are scientists doing now to improve those systems?

    There was no warning system in the Indian Ocean The tsunami did show the value of having one, and many governments are stating that one like the system in the Pacific Ocean needs to be put into the Indian Ocean.

    Scientists are working to expand the coastal and deep ocean measurement systems, improve the global earthquake measurement array, do more detailed tsunami modeling using computer models, help to educate the public on looking for natural signals of tsunamis (earthquake shaking, withdrawal of water from shore, roaring sounds from the ocean), and improving communication systems to warn people quickly in potentially affected areas.

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    Authority: Dr. Hal Mofjeld, NOAA Center for Tsunami Research

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