PRISM - American Society for Engineering Education - Logo - APRIL 2005 - VOLUME 14, NUMBER 8
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Send in the Engineers - Soon after the disaster, U.S. researchers headed to tsunami-ravaged Sri Lanka to learn what they could about mitigating such catastrophic destruction in the future. - A solitary building remains barely intact in a barren, debris-littered landscape that was once filled with brick houses in the town of Kalmunai. Here, the tsunami reached a height of more than19 feet killing, perhaps more than a 1,000 people. - Photograph by Philip Liu

By Thomas K. Grose

On the morning of Dec. 26, 2004, a massive earthquake along the Sumatra Fault, lying off the coast of Indonesia, triggered a huge tsunami, the likes of which the world had not seen in 45 years. Huge waves spawned by the quake devastated coastal communities in 11 south Asian countries. As of this writing, the death toll stood at 154,000, but the final tally will likely near 300,000. Yet, experts say, the fatalities caused by the Asian tsunami could have been far fewer, even without the sophisticated warning systems found along tsunami-prone coastal areas of the United States. They blame a lack of public education, shoddy building design and construction, and poor zoning for the huge loss of life. To help ensure that future tsunamis are less lethal, at least two teams of researchers led by American engineering professors headed to the tsunami-ravaged region in early January to survey the damage.

Unlike hurricanes and earthquakes, tsunamis are relatively rare natural disasters, a fact that makes predicting their behavior difficult. Hydrologists and hydrodynamicists use numerical models to forecast how tsunamis will interact with land and buildings, and that information can be used for warning systems, for public education, and to improve building and zoning in tsunami-threatened areas. And evidence amassed in the wake of a tsunami helps researchers to fine-tune and improve those models.

"Going out into the field and getting data is one of the most important things you can do in tsunami science because the events are so very rare," explains Patrick Lynett, an assistant professor at Texas A&M University's Ocean Engineering Program. Lynett was part of a team of eight researchers—engineers, geologists, and hydrogeologists from American universities as well as the U.S. Geological Survey—who spent a week in Sri Lanka, mostly on its east and south coasts. That team was led by Philip Liu, a professor of civil and environmental engineering at Cornell University. Harry Yeh, a professor of ocean engineering at Oregon State University, led a second team to the east coast of southern India, where it spent five days in the field, covering about 215 miles. His six-member team included two Indian researchers—a seismologist and an ocean scientist—as well as a social engineer from Japan.

Researchers face severe time constraints while trying to get into disaster zones. They must wait until critical rescue missions and body collections are mostly complete, but if they wait too long, key evidence might disappear as cleanups commence. "This trip was timed well—there was plenty of evidence," says Liu, whose team arrived in Sri Lanka in early January.

The two key things the engineers were trying to learn were the maximum water levels onshore and the inundation zone, or how far inland the water came. They looked for waterlines and mud marks on buildings and tree damage. How high the water reached tree trunks is very clear, Liu says. "The tree bark is torn apart." Debris hanging in tree branches can also indicate water levels, while debris lines denote how far the water came ashore. The accumulated evidence, Lynett says, "can give you a whole profile of the tsunami."

This tree, nearly uprooted by the surging water, was about 27 yards from the shoreline, in the village of Kinniya. Here, the tsunami reached about 13 feet.  Photo by Patrick LynettMost of the areas in Sri Lanka are relatively flat, and water levels there ranged from around 10 to 20 feet. But where elevations were steeper, the water raged even higher, up to around 38 feet in parts. "It [the water] just shoots right up the slope," Lynett says. The amount of inundation also varied. In some locales it petered out after about 160 feet; in other areas, it flowed inland about a mile and a quarter. Water levels measured by Yeh in India ranged from around 9 feet to 16 feet at Nagapattinum, where 6,000 people perished.

Learning From the Past

Those data are compared with existing models. The researchers are finding that in some cases their models were quite accurate, while other times they overestimated levels in some areas and underestimated in others. The data can also be calculated back to their source to help scientists get a better idea of what the seafloor looks like where underwater quakes occur. While scientists can quickly measure how much energy is released from a quake, the question of how the ocean floor was displaced, how the fault ruptured, for example, remains a mystery.

The Sri Lanka team found that some surviving buildings that faced the ocean nevertheless had their back walls blown out. As the water filled those buildings, the growing pressure forced the back walls to burst.

A researcher measures the water level in a destroyed house in the village of Kinniya. Mud lines on its walls shows the water flowed to a depth of about 8 feet.  Photo by Patrick LynettBoth teams also found deep scarring on the foundations of some buildings. They determined that as the water was funneled between rows of houses and buildings it accelerated. As the charging water hit the corners of buildings, whirlpools formed that scarred and undermined the foundations of buildings erected on sand. Yeh called this finding "very significant" for the future design of tsunami-proof buildings.

Because the tsunami struck during daytime and inundated many populated areas, the researchers were also able to gather eyewitness accounts. Indeed, Yeh says, there is also plenty of videotape footage and photographic evidence that is proving useful. Liu says that his interviews with locals lead him to conclude there were three waves that day, with the second being the strongest. Another boon for the researchers is remote-sensor images taken from government and commercial satellites, a first in post-tsunami investigations. Yeh calls the images amazing and very helpful. "In just two to three years the technology advancement has been incredible." In damage surveys, Yeh explains, "there are a lot of false clues" on the ground, and the satellite images can help investigators avoid them. For instance, Yeh came across several fishing boats piled together. He wasn't sure if the wave or the cleanup crews pushed them there. When he checked the satellite images taken not long after the tsunami receded, the boats were not there. He concluded the cluster was manmade.

As a tsunami races across open seas it can reach speeds of nearly 600 mph, as fast as a commercial airliner. But it slows greatly once it strikes land. The wave drops sediment as it slows, and geologists measure sediment deposits to factor the wave's land speed. That work is still being done, but Lynett says a ballpark estimate is between 20 to 30 mph.

Vital Signs

Researchers say ongoing, frequent public education efforts are the best way to avoid huge fatalities from tsunamis. "It is not too difficult to avoid loss of life," Liu insists. "And the cheapest way to mitigate a tsunami is with education," letting people know when a tsunami is likely (such as after a deep sea earthquake) and what the warning signs are. The people who died in Sri Lanka had only to head inland anywhere from a few dozen yards to, at most, a mile and a half to reach safety. And they could have done that had they known the danger signals, such as a receding sea.

Tsunamis occur relatively frequently in parts of Japan. As a result, people living in coastal areas know when to evacuate. When a 30-foot-high wave took out an entire Japanese village a decade ago, only three people died. In Sri Lanka, between the smaller first wave and the much larger second wave, the water receded far out into the seabed. Instead of using that opportunity to head for safe ground, some people wandered out to look at the seashells and floundering fish.

Education programs, however, can be weakened by the potentially long lag periods between tsunamis. After a few years, memories of the horrors and the need to heed warning signs can ebb like the tide. Yeh says a silver lining from this disaster is "now everybody is aware of the tsunami threat—at least for the next two or three years."

Zoning is a key safety measure, too. Liu's team visited the remains of a hospital that was built about 50 yards from the shoreline. All the facility's doctors, nurses, staff and patients—300 people in all—were killed. And, of course, the loss of so much medical personnel undermined the town's post-wave rescue efforts. Liu says "I still get very emotional about that, just thinking about it." But the tragedy underscored how important it is not to build critical infrastructure—hospitals, schools, and police and fire stations—in inundation zones.

Tsunami-resistant buildings can be designed and built, the engineers say, some perhaps with open designs on the lower floors that will let rushing waters flow through. Yeh envisions tsunami shelters, either single-purpose ones, or multipurpose buildings designated as shelters. Building code enforcement is a must, too. Liu saw many supposedly sturdy brick buildings demolished because they weren't reinforced.

The researchers confess to being awestruck by the destructive power nature can unleashThe researchers confess to being awestruck by the destructive power nature can unleash. Liu has been on many surveys, including one after a large tsunami battered Indonesia in 1992. But that wave hit an area that was sparsely populated. So the difference between that inspection and Sri Lanka's was stark, he says. "What shocked me was the magnitude of the devastation." This was Lynett's first survey, and he says words don't do justice in describing the destruction he saw. "It really was like an apocalypse."

Thomas K. Grose is a freelance writer based in Great Britain.

 

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