FRAMINGHAM, 11 MARCH 2011 - As the deadly tsunami generated by Friday's massive earthquake off the coast of Japan headed toward the United States, scientists at the National Oceanic and Atmospheric Administration's (NOAA) Center for Tsunami Research tracked its progress in real-time.
Dozens of deep-ocean tsunami-monitoring sensors more than three miles beneath the surface of the Pacific Ocean picked up information on the silent swell of water and transmitted it by way of a satellite to the Pacific Marine Environmental Laboratory in Seattle, Wash.
NOAA energy map shows the intensity of the tsunami caused by Japan's magnitude 8.9 earthquake. Darker red colors are more intense. (Image: Ho New/Reuters)
There, scientists crunched the data and quickly developed real-time predictions about how and when the tsunami would reach select locations in Hawaii, Alaska and the U.S west coast. The models predicted the wave arrival time, estimated wave height and the likely extent of inundation for about 50 communities likely to be affected.
When the data indicates danger, first responders in those communities get plenty of time to put evacuation plans into motion to limit human loss.
That kind of real-time, precision forecasting is a far cry from what was available in 2004 during the massive tsunami in the Indian Ocean, said Diego Arcas, a scientist with the NOAA Center for Tsunami Research (NCTR). That tsunami nearly obliterated the Indonesian coastline and that of other countries, killing hundreds of thousands without warning.
"It's almost a whole new world since 2004" in the field of tsunami forecasting, Arcas said.
Hundreds of people were killed and whole cities devastated in Japan by one of the worst earthquakes in over 100 years. The quake, which measured 8.9 on the Richter scale, generated a huge tsunami that inundated parts of Japan and put almost the entire Pacific coast line on high tsunami alert.
The effects of the quake, in terms of human loss and economic damage are expected to be huge.
The NCTR provides support to the national Tsunami Warning Center (TWC). Its mission is to develop numerical models for use by the TWC to develop faster and more reliable real-time tsunami forecasts. The technology used today by the NCTR is still being tested by the TWC for issuing tsunami warnings.
But it already represents the next step in tsunami modeling, Arcas said. Six years ago, there were just eight deep-sea sensors in the Pacific Ocean to monitor for tsunamis. Today, there about 30 of NOAA's Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys collecting such data and beaming it to the TWCs around the country.
There are also about 20 DART systems in the Atlantic and about half a dozen in the Indian Ocean.
When a tsunami travels across the ocean and passes over a DART system, the sensor measures the change in sea levels and reports it back to the TWCs. With first-generation DART sensors, alerts were triggered only when sea-level measurements exceeded specific thresholds.
Current DART systems feature two-way communications that allow forecasters to get measurement data on demand. The sensors are also so sensitive that they can detect an ocean level rise of less than one centimeter, Arcas said. "So we have the ocean instrumented much better than it was five years ago," he said.
The data gathered from these deep sensors give tsunami modelers more information to work with compared to the data generated by tidal gauges. Combining the improved measurement capabilities with historical data -- and data about bathymetry (ocean depth) and topography -- scientists can predict tsunamis far more accurately, he said.
In fact, given the right set of data, scientists at the NOAA today can develop simulations of up to four hours of tsunami activity in about 10 minutes, Arcas said. "Usually, the largest waves happen within the first four hours of a tsunami," he said. For first responders and emergency managers, "that is the most important information they want to get out of a warning."
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