OREGON STATE UNIVERSITY

Tsunami behavior, prediction a very complex task

03/29/2005

CORVALLIS, Ore. - The earthquake that hit near Indonesia yesterday does not appear to have caused the huge tsunamis that were generated by the event last December, illustrating the difficulty of predicting with certainty these catastrophic events, say experts at Oregon State University.

The earthquake itself appears to have occurred on at least part of the same subduction zone as the previous event, and has a magnitude that has been reported as high as 8.7, but there have been no reports of any significant destruction from tsunamis. The original earthquake was at least magnitude 9.0.

OSU experts, who operate the Tsunami Wave Basin at the O.H. Hinsdale Wave Research Laboratory, say it's critical that extensive research should continue on earthquakes, the tsunamis that result from them, their magnitude and directionality, preparation of infrastructure for tsunami resistance, and many other issues.

"Yesterday's earthquake event will give us much to study and learn from, not only in terms of scientific findings but also the social response to the event," said Harry Yeh, an internationally recognized expert on tsunamis and the Edwards Professor of Ocean Engineering at OSU. "It may be unrealistic to think that our warning systems and other approaches have improved much in East Asia in the short time since the December event, but we'll see what kind of progress we are making and how people reacted."

It's not without precedent for a major earthquake zone such as this to have two substantial earthquakes within a short period of time, Yeh said. But the type of tsunami, if any, that might be generated depends a great deal on the length of the fault that ruptures, its motion, the overall energy released and many other factors. And even that does not always predict with any certainty what direction a tsunami wave will take.

The issuance of tsunami warnings is always done after careful consideration, Yeh said, because of the social concerns and disruptions related to evacuation of low-lying coastal areas. An 8.2 magnitude earthquake in 1994 that occurred beneath the seas between Japan and Russia resulted in warnings of a significant tsunami for Hawaii. But that event never resulted in much of a wave, and was the source of some criticism about the personal and economic disruption it caused.

"Since the science of predicting tsunamis will never be perfect, there will always be some false alarms," Yeh said. "But that just can't be helped. In the science community we worry more about people becoming complacent, not taking these warnings seriously or understanding what they need to do to protect themselves if a tsunami event or warning does occur."

Yesterday's event also provides yet another reminder of the high level of tectonic activity on the "ring of fire," an area surrounding much of the Pacific Ocean which is among the most earthquake-prone regions of the Earth. It includes the West Coast of North America. The tsunami risk is highest in the Pacific Northwest, which is near the Cascadia Subduction Zone - an area quite similar to the subsea region near Indonesia that has now been the focus of two major earthquakes in three months.

Other research at OSU has also indicated that there may be a "clustering" of great earthquakes on the Cascadia Subduction Zone, during which they occur with more frequency, and that the region may be within one of those clusters right now - and possibly due for a great earthquake almost any time.

Dan Cox, director of the Hinsdale Wave Research Laboratory at OSU, said that yesterday's event also provides another reminder of the need to structurally prepare our coastal infrastructure well in advance for earthquakes and tsunamis. "Some researchers have predicted that there's a 15 percent chance of a major subduction zone earthquake and tsunami here in the Pacific Northwest in the next few decades," Cox said.

There are fairly good warning systems already in place today on the West Coast, and they might even be improved, Cox said, although for most people the primary warning they will get of a tsunami is the earthquake itself.

"But that type of warning, while helping to reduce some loss of life, won't do much to prepare our coastal cities and infrastructure to resist the damage from tsunamis," Cox said.

"In our work here at OSU we're learning more all the time about how to build things, where it's safe to site them, and what steps we can take to lessen the destruction from a tsunami," he said. "We can see in these events in Indonesia just how active subduction zones can be, and the damage they can cause. Our structural preparation for the events we know are coming is where a lot of the challenges remain, and there are still a lot of things we can do better in this area."