OSU Wave Lab: Simulated tsunami

Story Posted: Fri, Sep 14, 2007

By Carol Reeves
Gazette-Times reporter

First step in research looks at wave depth and speed

A 35-foot tsunami crashed into downtown Seaside at about 10:30 a.m. Thursday. Another one rolled in about 20 minutes later, followed by two more before the hour was up.

Fortunately, the giant waves didn’t cause any damage to the real coastal community of 6,000 people. But the surges — generated by the wave machine at the O.H. Hinsdale Wave Research Laboratory at Oregon State University — played havoc with a scale model of the town that researchers have built during the last three months.

Daniel Cox, director of the research center, said a magnitude 9 earthquake along the Cascadia subduction zone could result in a three-story wave slamming Seaside. The subduction zone, which lies less than 100 miles off the Oregon Coast and stretches from British Columbia, Canada, to northern California, is similar to the kind of geological fault that caused the massive tsunami in East Asia in 2004.

The Northwest has not seen such an event in 300 years, but scientists estimate there is a 14 percent chance one will occur in the next 50 years, he said. The tsunami would arrive within 30 minutes and coastal communities without an efficient evacuation plan would see thousands of casualties.

“What we’re looking at here are solutions,” Cox said. By studying the effect of the tsunami on models of real buildings according to how they are actually clustered together, researchers can begin to develop evacuation strategies that will minimize the loss of life.

The first phase of the study is to measure how deep the water is relative to the “ground” and how fast it’s moving — critical pieces of data in estimating the potential wave force, Cox explained. The next step is to determine how the tsunami will impact buildings, followed by a study of what happens to the debris unleashed by such a huge wave of water.

Practically speaking, the information gained can help cities design better evacuation routes and establish construction guidelines for buildings that can withstand the force of a tsunami.

People naturally try to escape a tsunami by moving inland, Cox said, but sometimes, the better option would be “vertical evacuation” inside nearby buildings that are tall enough and strong enough to resist a huge wave.

Dr. Harry Yeh, an OSU civil engineering professor and tsunami researcher, said many communities on the coast of Japan have tsunami towers that people flee to when a tsunami warning is issued. In other places, there are raised concrete platforms people climb onto in the event of a tsunami.

As part of his research, Yeh has developed a computer simulation that tracks the evacuation of Seaside after a tsunami warning. His research shows that a scenario that includes two theoretical tsunami shelters close to the beach dramatically reduces the potential death toll when compared with the city’s current plan directing people east to higher ground.

Cox said Seaside was chosen as the “model city” for this particular round of wave research for several reasons. It’s a popular tourist town where the population swells dramatically on the weekends and in the summer. The topography is also unique in that most of the town east of the beach slopes down and evacuees must cross two rivers to get beyond the inundation zone.

Those bridges may not be standing after a major earthquake, and out-of-town visitors are likely to slow the evacuation process if they don’t know where the safe zones are.

Current research efforts at the wave lab are important, Yeh said, because unlike earthquakes, there’s always at least a short lead time to warn people about a tsunami.

“We need to determine where the safe places are for people — how high is tall enough? Which existing buildings would withstand a tsunami or when building new hotels or structures along the beach, can we make them strong enough to be tsunami-resistant?” he asked.

“As best we can, we need to minimize the lives that might be lost,” Yeh said.