Researchers Study Tallest Man-Made Tsunami
YOKOSUKA, Japan — At the far end of a long trough, a bulge of water appears. Seconds later, the wave rips through the wall of a room with such fury it splinters the wall and washes away the furniture and a mannequin standing behind it. From seabed to crest, the 8-foot-tall wave is the world’s tallest man-made tsunami, Japanese scientists at the Port and Airport Research Institute’s Tsunami Research Center said on Wednesday.
But while size is critical in tsunami research, the scientists aren’t concerned about breaking records. They’re trying to recreate the awesome force of the wave.
“The bigger the tsunami we make, the more accurately we can reproduce its actual destructive power,” Taro Arikawa, the project’s leader, said during a demonstration of the simulator.
By determining the power and behavior of a tsunami, the scientists hope to devise better seawalls and more precise evacuation plans for coastal communities at risk of a direct hit, Arikawa said.
Such safety measures might have made a difference in saving lives in the Indian Ocean earthquake tsunami in December that killed nearly 180,000 people and left another 50,000 missing.
“Based on this data, we can create a hazard map showing which areas might sustain the worst damage from a tsunami. That would let people know which way to run,” said Arikawa.
The United Nations has led an effort to set up a tsunami early warning network for the Indian Ocean similar to the one that now protects the Pacific. The U.N. Educational, Scientific and Cultural Organization says such an offshore system would cost $30 million, and could go into operation by mid-2006.
Japan, which has one of the world’s most advanced warning systems, uses a supercomputer linked by satellite to an array of seismic, pressure and tidal sensors that can make forecasts about the size of waves approaching the country’s coastline.
Onshore, however, it’s a different story.
Experts say it’s impossible to know whether a tsunami will burst past seawalls and demolish buildings or flow harmlessly on the beach because that depends on the shape of the seabed.
Many researchers have studied the mechanics of the killer waves. Oregon State University’s O.H. Hinsdale Wave Research Laboratory, for example, has built a tank and unleashed man-made tsunami on concrete bridge columns. Others in Russia, Germany and Spain have tanks as well.
But the Tsunami Research Center has come closer than anyone else to mimicking – and measuring – the waves’ actual power.
In a narrow, concrete tank slightly longer than a football field, a giant vertical slab lurches forward, creating a wave. Traveling at about 10 yards per second, the wave pounds into a 4-inch-thick wooden wall, tossing a table, bookshelf and a mannequin into the air before sweeping them away. Tiny sensors record the force of the impact at different heights.
Arikawa compared the pounding to that of a car hitting an object at 25 miles per hour.
“We estimate that a real 33-foot-tall tsunami would exert about 25 times the force of our wave here,” he said.
Measuring the sheer force of a tsunami is only part of the equation. Other experiments examine how the waves can churn up the sandy seafloor and destabilize the foundation of coastal towns, or test how different types of building materials and seawall designs block the wave.
Some experiments look at all three factors at once.
“We can simultaneously monitor the wave as well as its effect on the seabed and impact on a building,” said Takayuki Yamane, the institute’s director of marine environment engineering.
Plugging that data into a program might one day allow coastal communities to know how far inland a tsunami might reach or select buildings that could withstand a tsunami and devise strategies directing residents to them, Arikawa and others said.
They are also at work on a seawall that would flutter to dampen the waves’ force and another made with an inner core that would double the wall’s height by automatically rising in response to the sudden force of a monster wave.
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