OREGON STATE UNIVERSITY

Lessons from Chile: Tsunami science, sociology have a ways to go

03/01/2010

CORVALLIS, Ore. – Scientists from around the world tracked tsunami waves across the Pacific Ocean following the massive 8.8 magnitude Chilean earthquake and warnings were issued in Hawaii, Japan and along the West Coast of the United States.

After evacuations and inconvenience, huge waves never materialized and now many in the news media and public are questioning whether such warnings were a good idea.

All this underscores that there is still much we don’t know about the behavior of tsunamis – or people.

“The Chilean event demonstrates that tsunami research is still immature,” said Harry Yeh, an Oregon State University professor of engineering and internationally recognized tsunami expert. “Tracking tsunamis across the ocean is one thing, but predicting how they will react when they reach the continental shelves is something that needs more work.”

So does the sociological impact of coastal hazards. At the same time residents in Hawaii were being evacuated from coastal regions, many people living on the West Coast actually flocked to the beach to see if a tsunami would materialize. And many of the coastal visitors weren’t at high-elevation overlooks – they were on the beaches themselves.

Despite such behavior, Yeh says that when in doubt, warnings should be issued.

“Even though many specialists looked at the tsunami as it was moving across the ocean and felt it would not be on the same level as the 2004 Indian Ocean event, it would have been difficult to not issue a warning,” Yeh pointed out. “After all, there was a fairly significant tsunami present in the ocean, and there is still a great deal of uncertainty about their behavior as they near shore.

“When there are human lives at stake,” Yeh added, “you have to take the cautious approach.”

Chris Goldfinger, an OSU marine geologist and one of the foremost experts on the Cascadia Subduction Zone, worries that the public won’t pay attention when tsunami warnings are issued in the future.

“One of these days, we will have a major earthquake with an associated tsunami warning that will need to be taken seriously,” Goldfinger said. “Having a series of false alarms may be doing some harm, from that standpoint. One area that could be improved would be for the warning centers to make better use of geological information, both at the earthquake source and at arrival locations.”

Such information is improving every year. Goldfinger, in fact, is principal investigator on a project to map the seafloor off the Oregon coast. With funding from the Oregon Legislature and the National Oceanic and Atmospheric Administration, he and his colleagues are creating the most detailed maps of the seafloor ever generated.

When completed, these maps will have a resolution of a half-meter or better, and cover 34 percent of State of Oregon waters and 75 percent of its rocky reefs. They will record every bump, depression, reef and boulder, allowing scientists to create more accurate tsunami inundation models.

Such maps will be invaluable in the future, but they don’t exist for many locations around the world. And that is part of the problem in predicting near-shore tsunami behavior, according to Solomon Yim, director of the O.H. Hinsdale Wave Research Laboratory at Oregon State, which has one of the largest, most sophisticated tsunami wave research facilities in the world.

“The exact height of tsunami waves is very difficult to predict, because some regions tend to focus incoming waves and make them unexpectedly large,” Yim said, “while other areas don’t have much run-up at all.”

Yim said the origins of tsunamis begin with the earthquake and how it affects the movement of the seafloor. If large portions of the seafloor move up or down, it will create a tsunami. If the movement is horizontal, a tsunami won’t materialize.

“When you look at both of those motions on a seismometer, however, they can look very similar,” Yim said. “The only way to determine exactly what happened is to scan the seafloor for the next several days or weeks, which doesn’t lend itself to immediate predictions about the size and scope of a tsunami.”

Devastating earthquakes have struck recently in Indonesia, Haiti and Chile, and research suggests that the Pacific Northwest may be due for its own massive earthquake. Goldfinger’s research into the history of the Cascadia Subduction Zone has found evidence of nearly two dozen earthquakes over the past 10,000 years with magnitudes that likely exceeded 8.5. These quakes occur every 300 to 500 years, he pointed out, and the last one was in 1700.

“A major earthquake and tsunami could happen here literally at any time,” Goldfinger said.