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Photos Where the Faults Are
Buoy Toys The state-of-the-art, $200,000 DART buoys are only half of the picture, McNulty explained. The other half of the system sits on the ocean floor, sometimes thousands of feet down. This sea floor unit measures changes in water pressure, which can be converted into water depth, and transmits the data via an acoustical modem to the buoy on the ocean surface. Each buoy uses satellites to relay up to 15 minutes of data to two NOAA tsunami warning centers in Hawaii and Alaska, which operate 24 hours a day, seven days a week. At the warning centers the data is fed into 26 new tsunami generation models. If buoys near the epicenter detect a large tsunami, and the models forecast it coming ashore, forecasters can broadcast specifics about where, when and how large the tsunami will be when it hits. People in communities equipped to get out the word ought to have plenty of time to head for higher ground. If, on the other hand, it looks like no significant tsunami is on the move, forecasters can cancel any tsunami warning issued at the time of the quake. Over the past three years, there have been plenty of opportunities to test the growing system. "We've had six measurable tsunamis since (the Indian Ocean event)," said Bernard. The largest was a magnitude 8 quake very near the coast of Peru last August. Although a few casualties occurred near the epicenter of that quake -- too close for any warning other than the shaking Earth -- the tsunami that propagated out to sea was accurately forecasted using DART data. The successful forecast was written up by Bernard and his colleagues and published in the Feb. 28 issue of the journal Geophysical Research Letters. Subduction Secrecy Another hard-earned lesson from the Indian Ocean tsunami regards what places are most vulnerable to large tsunamis. At the time, seismologists thought they had good hypotheses about which subduction zones were the most dangerous. But it turns out a lot of those ideas, now tested on real tsunamis, were off the mark. "Immediately following that big earthquake (on Dec. 26, 2004), they said there wouldn't be another near there for centuries," Bernard recalls. Then three months later there was a magnitude 8.7 quake just to the south. Luckily, its tsunami was aimed at Antarctica, posing problems for penguins perhaps, but not for human settlements. "It just tells you how poor our ability is to predict these things," said Bernard. "A tsunami guy like me says [to the seismologists], 'you guys don't know when it's going to happen,'" or where, for that matter. Even the location of the Great Sumatra-Andaman Earthquake defied the prevailing thinking, occurring in a part of a subduction zone considered low risk. The DART buoys monitor every subduction zone, as if they all could create killer waves. The final and ongoing part of the warning system, however, is to teach the public what to do in the event of a tsunami, said McNulty. After all, the best warning system in the world is useless if people don't know how to respond. Related Links: Larry O'Hanlon's blog: Earth Impacts |
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