December 31, 2004
The type of devastating tsunami that struck the southern coast of Asia is entirely possible in the Pacific Northwest of the United States, according to experts at Oregon State University.
The newest studies on the Cascadia Subduction Zone off the coast of the Pacific Northwest have identified a "clustering" of great earthquakes of the type that would cause a major tsunami.
The studies show the quake zone has already experienced four major quakes in the past 1,600 years, which could mean the cluster is over and has entered a quiet period. Or, the experts say, since the last major quake took place in the year 1700, and the average interval between them is 300 years, the next big one could be around the corner.
"The Cascadia Subduction Zone has the longest recorded data about its earthquakes of any major fault in the world," said Chris Goldfinger, an associate professor of marine geology at OSU and one of the leading experts on this fault zone. "So we know quite a bit about the periodicity of this fault zone and what to expect. But the key point we don't know is whether the current cluster of earthquake activity is over yet, or does it have another event left in it."
According to Goldfinger, there are only two places in the United States with active subduction zones, or major areas where one of the Earth's great plates are being subducted, or forced underneath the other. One is in Alaska, the site of the great earthquake of 1964. The other is the Cascadia zone, a 600-mile long fault zone that runs from Cape Mendocino in California to Vancouver Island in southern British Columbia.
Major studies have identified 17 earthquake events in the area that have reached a magnitude of 9.0 on the Richter scale and triggered major tsunamis.
According to Goldfinger, there are remarkable geologic parallels between what just happened in East Asia and what could happen in the Pacific Northwest. The Asian event happened where the India plate was being subducted beneath the Burma microplate, and it ruptured – for the first time since 1833 – along a 600-mile front that is just about the same length as the Cascadia Subduction Zone. That earthquake happened as the Indian plate moved toward the northeast beneath Asia, just like the Juan de Fuca plate in the Pacific Northwest before it disappears beneath the North American plate.
What happened in Asia may give a vivid demonstration of the geologic future of the Pacific Northwest. For hundreds of years, these subduction zone plates remain locked, releasing little of their tension. The plate that is being subducted is forced down, while the plate above bulges upward. Then, in a few minutes of violence every few centuries, the forces are released. The upper plate moves seaward, and a massive tsunami can be produced along with catastrophic destruction from earthquake shaking.
"In the case of the Cascadia Subduction Zone, you could have an area of ocean sea floor that's 50 miles wide and 500-600 miles long suddenly snap back up, causing a huge tsunami," Goldfinger said. "At the same time, we could expect some parts of the upper, or North American plate to sink one to two meters. These are massive tectonic events. Subduction zones produce the most powerful earthquakes and tsunamis in the world."
The question, Goldfinger says, is not whether or not the Cascadia Subduction Zone will break again. It's when. And that's where the study of past events may shed light on the present.
"The loss of human lives from this latest tsunami is staggering," said Harry Yeh, an internationally recognized tsunami expert and the Edwards Professor of ocean engineering at OSU. "We have to ask, 'why?' Clearly, they didn't have the same kinds of warning systems that we have on the West Coast of the U.S. That is why the research that we do here is so important. As tragic as the event is, it also represents a learning opportunity, and we have a responsibility to learn from it what we can."
Robert Yeats, professor emeritus of geosciences at OSU, agrees that the reason for the great loss of life in Sri Lanka, India and other Asian countries was the lack of a tsunami warning system.
"That much loss of life wouldn't happen here for either a local or distant tsunami because of warning systems operated by the National Oceanic and Atmospheric Administration, with laboratories in Newport and Seattle," Yeats said. "NOAA would record the earthquake on seismographs and issue bulletins about the progress of a tsunami. Deep-ocean buoys off the Aleutian Islands and Cascadia would also record the passage of tsunami waves in the open ocean."
For a tsunami caused by a Cascadia earthquake, people on the coast would have about 15 minutes to get to high ground, Yeats said. Emergency managers of coastal counties have told residents about planning escape routes from a tsunami, and schools in Seaside, Ore., have had tsunami evacuation drills. Some coastal communities also give warnings through a siren for those vacationers who aren't keeping up with the news. Visitors to the coast should look for the blue and white tsunami warning signs on Highway 101 and some beach areas.
"In the Pacific Northwest, there is no way to tell whether the next Cascadia earthquake will strike tomorrow or 100 years from now," Yeats said. "We must prepare for the worst case scenario, both in tsunami escape preparations and in not building in potential tsunami inundation zones."
SOURCE: World Net Daily