Wednesday, March 3, 2010

Taking Aim At Tsunami Forces

Recent catastrophic earthquakes and tsunamis have taken center stage around the globe. But scientific research now under way could substantially reduce property damage and loss of life from such natural events.

In September 2009, a magnitude 8.0 earthquake struck Samoa and the American Samoa Islands. Nearly 20 minutes later, villages were inundated by four tsunamis ranging from 15 to 20 feet high and traveling as far as a mile inland from the coast.

Fast-forward to Jan. 12, 2010, when a much more destructive earthquake occurred in Haiti’s capital of Port-au-Price. By Jan. 24, at least 52 aftershocks were reported by the Haitian government, and between 217,000 and 230,000 people were identified as dead. Beyond that, 300,000 people were reported as injured and an estimated 1 million people were reported as homeless. The government also estimated that over 250,000 residences and 30,000 commercial buildings collapsed or were severely damaged.

Last week, an earthquake struck in Chile. This was recorded as an 8.8 magnitude quake, but the epicenter was not as close to a large population as was the Haitian earthquake.

To date, the death toll is close to 1,000 -- far different than Haiti for several reasons. First, Haiti’s quake was much closer to the land surface. Second, the epicenter of the Haitian earthquake occurred in Port-au-Prince, where millions of people live. Third, Chile was much better prepared for this kind of catastrophe. Haiti is a much poorer country with virtually no provisional funding for such an event.

Tsunamis often occur shortly after large earthquakes and certainly the Chilean disaster was no exception. After the December 2004 Indian Ocean Tsunami, several researchers recorded the effects of how that event engulfed several communities minutes after residents felt the severe earthquake on land.

Mary Beth Oshnack from Notre Dame and civil engineer Tracy Kijewski-Correa modeled a hotel in Thailand that sustained structural damage in the tsunami of 2004. Since there is limited data on structural damage from tsunami loadings, the team compared the failure modes and moments of their simulation model to the more thoroughly studied natural hazards, such as the Northridge earthquake and Hurricane Katrina.

From their analysis, they came up with recommendations on how to improve the construction of buildings within the tsunami inundation zone. A key finding was that elevating structures or using breakaway walls drastically reduces forces that can damage a building because these methods allow an incoming wave to simply pass through the structure.

Further, Dan Cox at the Oregon State University has collaborated with the O.H. Hinsdale Wave Research Institute (part of the National Science Foundation’s Network for Earthquake Engineering Simulation).

Earthquake-generated tsunamis threaten certain areas of the United States, including the Cascadia Subduction Zone of the Pacific Northwest. Such a tsunami would give residents in those coastal communities little time to respond or evacuate to higher ground.
Researchers from OSU are investigating ways to improve preparedness within the threat zone. The team has come up with two approaches to protecting target inhabitants during a tsunami:

• Constructing vertical evacuation structures within the inundation zone can save lives by moving people above and out of threat.

• Providing communities with small seawalls can reduce tsunami forces on landward structures by deflecting and incoming wave upward.

Scientists are incorporating state-of-the-art wave-makers to simulate actual tsunami conditions. Walls of various materials are subjected to wave loading. Researchers have tested a wide variety of walls over a range of wave conditions. Each time data is collected about the wave profile, such as the wave’s height and speed, and the wall’s reaction, such as the force, pressure and deflection from the incoming wave.

Their project has consisted of five key experiments and generated exhaustive data. The goal is to reduce structural damages and loss of life during a tsunami event.

One of the experiments found that small seawalls cause a skyward deflection of an incoming tsunami. This consequently reduces wave energy and force on structures directly adjacent to the wall. These seawalls are inexpensive and easy to build.

Other research is investigating how tsunami forces change with the distance to the shoreline. This information can help community planners establish setbacks and decide on the best location for high-profile buildings such as schools, hospitals, and evacuation structures.

While very practical, the research is also quite technical. The experimental data is compared to numerical simulations, small-scale experiments and published theoretical models.

Though these comparisons, researchers can determine if their experimental data is accurate. They can even find the most effective and efficient way to model tsunami inundation and loading. Large-scale experiments are costly. If the computer simulations are accurate, a whole new range of research and design possibilities will be discovered to ultimately save lives.

This post is courtesy of TechMan, a contributor who follows trends in technology, science, business and industry.

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