INGLÊS

Tsunami science:

advances since the 2004 indian ocean tragedy

The Indian Ocean tsunami was one of the worst natural disasters in history. Enormous waves struck countries in South Asia and East Africa with little to no warning, killing 243,000 people. The destruction played out on television screens around the world, fed by shaky home videos. The outpouring of aid in response to the devastation in Indonesia, Sri Lanka, Thailand and elsewhere was unprecedented.

The disaster raised awareness of tsunamis and prompted nations to pump money into research and warning systems ((1)). Today (Dec. 26), on the 10th anniversary of the deadly tsunami, greatly expanded networks of seismic monitors and ocean buoys are on alert for the next killer wave in the Indian Ocean, the Pacific and the Caribbean. In fact, tsunami experts can now forecast ((2)) how tsunamis will flood distant coastlines hours before the waves arrive. But hurdles remain in saving lives for everyone under the threat of tsunamis. No amount of warning will help those who need to seek immediate shelter away from beaches, disaster experts said.

Since 2004, geologists have uncovered evidence ((3)) of several massive tsunamis in buried sand layers preserved in Sumatran caves. It turns out that the deadly waves aren’t as rare in the Indian Ocean as once thought. “We had five fatal tsunamis off the coast of Sumatra prior to 2004,” said Paula Dunbar, a scientist at NOAA’s National Geophysical Data Center. Over the past 300 years, 69 tsunamis were seen in the Indian Ocean, she said. Despite the risk, there was no oceanwide tsunami warning system in the region. Now, a $450millionearly-alertnetworkisfullyoperational,thoughitisplaguedwithequipmentproblems.Essentiallybuiltfromscratch,the<span>$450 million Indian Ocean Tsunami Warning System includes more than 140 seismometers, about 100 sea-level gauges and several buoys that detect tsunamis. More buoys were installed, but they have been vandalized or accidentally destroyed. The buoys and gauges help detect whether an earthquake triggered a tsunami.

Getting the warnings down to people living in remote coastal areas is one of the biggest hurdles for the new system. Not all warnings reach the local level. And not every tsunami earthquake is strong enough to scare people away from shorelines. In Sumatra’s Mentawai Islands, a 2010 tsunami killed more than 400 people because residents failed to evacuate in the short time between the earthquake and the tsunami’s arrival. The shaking was simply not strong enough to trigger people’s fear of tsunamis, even though islanders had self-evacuated ((4)) after a 2007 earthquake, according to an investigation by the

University of Southern California’s Tsunami Research Center. There was also no clear-cut warning ((5)) from the regional tsunami alert system.

Another hurdle is learning how to accurately forecast reflected tsunami waves. The 2004 Indian Ocean tsunami ricocheted off island chains, and some of the worst flooding arrived unexpectedly late in places like Sri Lanka and Western Australia. “I found a boat on the middle of the road, and at that point knew it was a tsunami,” recalls Charitha Pattiaratchi, a University of Western Australia tsunami expert who was driving on a coastal Sri Lankan road on Dec. 26, 2004. “I came to the conclusion that I was safe. Well, I was wrong ((7)). Twenty minutes later there was seven meters of water where I had been standing, and two hours later there were still more waves coming.”

A tsunami warning can go out just five minutes after a submarine earthquake raises or lowers the seafloor, thus launching a tsunami. For more detailed predictions of the wave’s impact, such as the extent of flooding, scientists rely on data collected by seismometers, GPS stations, tide gauges and buoy systems, which ((8)) is relayed by satellite to warning centers. Computer models then convert the data into detailed tsunami simulations, which are based on more than 2,000 real-life examples.

After an earthquake, scientists with NOAA’s tsunami warning centers now spend about an hour working out the details of a tsunami forecast, said Vasily Titov, director of NOAA’s Center for Tsunami Research. The results project when the wave will arrive at shorelines and harbors, estimate tsunami- induced currents and gauge the height of the waves. The agency’s goal is to dramatically reduce that hour- long delay ((9)). “We’re now at the point where we want to do it in five minutes,” Titov said. That means building out the seismic network ((10)), getting a faster response from the sea-level sensors and speeding up the computer forecasts. “When these three components come together, then we can save everybody ((6)),” Titov said.

(By Becky Oskin, Senior Writer. Adapted from http://www. livescience.com/49262-indian-ocean-tsunami-anniversary.html. December 26, 2014.)

In paragraph 5 tsunami expert, Charitha Pattiaratchi, recalls the critical moments she faced in a Sri Lankan road on Dec.26, 2004. Which of the following proverbs best applies to the statements “I came to the conclusion that I was safe. Well, I was wrong.” ((7)):