March 6, 2005
By Winston Ross
The Register-Guard
FLORENCE - On the open ocean, you won't even feel it.
Not the magnitude 9 earthquake radiating from two tectonic plates that merge just off the Pacific Coast; not the resulting tsunami, traveling at jetliner speeds. As the quake wreaks havoc on land, rattling buildings and bridges into pieces, triggering massive landslides and turning soil into quicksand, the wave will silently surge toward shore like any other.
But as the wave strikes the shallows, it rises up, transforming itself from a barely detectable swell to a 50-, 80-, maybe even a 100-foot wave in some places. The tsunami will powerfully meet whatever dares confront it - homes, automobiles, people - with chaotic force.
As it encounters obstacles, the wave will create swells that crash north, south and back toward the sea. On land, the tsunami will surge toward low-lying areas, adding uprooted trees, dock pilings and cars to its arsenal and mangling or killing anyone who can't get out of the way.
Then it will happen again. And again. The waves will diminish in speed and force, but grow more deadly as people on the coast assume the threat has passed - when, in reality, the ocean will simply be gathering more weaponry in the cars, refrigerators, broken houses and propane tanks it earlier dragged into the water.
"This will have more damage than a nuclear bomb," said Tillamook County emergency manager Tom Manning at a tsunami preparedness workshop in Salem last week.
George Priest knows all this because he can simulate tsunamis with a sophisticated computer program, which sorts through a mind-numbing combination of factors to predict how and where a tsunami will strike Oregon.
The question he can't answer is when. Still, this work is crucial, because the same computer programs create evacuation maps for coastal communities. Emergency officials rely on Priest's estimates to tell people where it's safe to go.
Until the Indian Ocean tsunami the day after Christmas, however, the models were incomplete. Priest and other scientists with the Oregon Department of Geology & Mineral Industries had only weak or ancient analogies to compare past earthquakes and tsunamis with what would probably occur if the two plates that form the Cascadia subduction zone shake again.
Old earthquakes lack recorded data. Recent earthquakes weren't nearly as large, or they happened at night, impeding eyewitness accounts that help researchers figure out the waves' height, path and force.
Now scientists have a perfect test case. Of the many coastlines struck by the Dec. 26 quake - which killed 180,000 people and left 5 million homeless in 11 nations - none matches Oregon's more closely than that of Sumatra Island.
The fault lines that caused that quake make up the Sumatra subduction zone, which last produced a magnitude 9 temblor in 1833. There, the India plate subducts, or dives under, the Burma plate, much like the two plates that make up Cascadia. And the zone's distance from Sumatra's coast is about the same as Cascadia's is to Oregon.
But chaos reigns in Sumatra, where a civil war and suspicion of outsiders have combined with the tsunami's own havoc to make sending a team of scientists to the region problematic. So far, only a few researchers have traveled there and they've recorded waves twice as high as anyone previously measured.
"It's one of the largest tsunamis in modern history. It will be the best-documented tsunami ever. It was even caught on a satellite image, when it was still in the open ocean," Priest said. "It's possible this event will revolutionize the way we do tsunami warnings internationally and the way we simulate tsunami waves with computer software."
ALL QUIET ON THE WESTERN FRONT
For centuries, the Cascadia subduction zone has been quiet.
Too quiet.
To the south and north of these locked-tight tectonic plates, tiny earthquakes have rattled the consciousness of coastal residents throughout history.
But Cascadia is eerily silent.
"It doesn't even give up little bitty earthquakes," Priest said.
That is not good news for the Oregon Coast.
The 650-mile fault runs from British Columbia to Northern California. It is a member of the family of fault lines known as the Ring of Fire in the Pacific, where more than half the world's volcanoes are found and 80 percent of the world's tsunamis are generated.
The fault is where the Juan de Fuca plate is forced beneath the Continental plate, locked so tightly that they only move a few centimeters each year. As they remain locked together, pressure builds. Eventually, they will slip. It's insignificant in the grand scheme of geological time, but a disaster that could kill thousands along the Pacific Coast.
"Subduction zones produce the most powerful earthquakes and tsunamis in the world," said Chris Goldfinger, an associate professor of marine geology at Oregon State University and a leading expert on the Cascadia fault.
A 1998 state study showed that an 8.5 magnitude earthquake on the Oregon Coast would produce $11.8 billion in economic losses, kill or injure 6,800 people and destroy 54,000 buildings.
But after decades of debate, scientists agree that the earthquake's size will probably be magnitude 9 or greater, releasing many times more energy. About 90,000 people are estimated to live within .6 of a mile of the Oregon Coast. Millions visit each year.
"It's going to be a mess," said Bob Eaton, who has worked for years to educate his guests about tsunamis as general manager of the Inn at Spanish Head in Lincoln City. He told emergency managers at last week's workshop, "I don't know how you people are going to handle them after I get them to the emergency room."
FALLING INTO THE SEA
The earthquake alone will cause incredible destruction on the Oregon Coast and in the Willamette Valley. From its shaking, buildings will crumble, bridges will collapse, roads and airport runways will buckle, dams will burst and water lines will break, leaving emergency officials helpless to battle inevitable fires.
And in areas with a high water table and sandy soil - prolific on the Oregon Coast - the ground will liquefy, as water and soil placed under intense pressure turn to mush for the duration of the quake.
Then there are landslides. In 2000, the 600-foot-high Cape Creek slide between Florence and Yachats closed U.S. Highway 101 for months as workers removed tons of debris that had broken loose from the hillside above it and cascaded down onto the highway.
A magnitude 9 earthquake would cause entire chunks of the coast to fall right into the sea. On steep slopes, landslides that dwarf the one at Cape Creek would bury U.S. 101 - cutting off relief efforts for thousands of residents, making them reachable only by helicopters and boats.
"Every single bit of coast highway is going to be clipped where we have these steep slopes," Priest said. "We all know how long it took ODOT to fix just one. Parts of the shoreline will have to be abandoned."
WARNING TIMES WILL VARY
Eventually, the shaking will stop, and a new clock will start ticking - on the incoming tsunami. The plates will push the water above them with herculean force, creating a wave offshore that will travel at speeds of up to 600 miles per hour, until it hits shallower water moments after it has formed.
People in Seaside will have the most warning on the Oregon Coast - the town is farthest away from the fault line. Places closest to the fault, such as Cape Blanco, will have as little as 10 minutes from the start of the quake to when the first wave strikes. But some of those landscapes are better protected from the wave.
What happens when the water reaches shore is guesswork. Tsunamis react to whatever they hit, bouncing in all directions until the water subsides. They also come in sets. A magnitude 9 Cascadia quake could produce waves that relentlessly bash the coast for eight to 10 hours.
For Florence, the Siuslaw River estuary and the spit between it and the ocean will serve as a buffer, slowing the tsunami considerably before it reaches people. It's far more likely to cause flood damage than by the sheer force of a towering breaker. Water levels probably wouldn't change for 30 minutes. That's why this town's "inundation map," showing which areas will most likely be swamped by the tsunami, still isn't complete. The estuary makes predicting the wave too complicated.
A QUESTION OF WHEN, NOT IF
Everything else about an earthquake and tsunami here is nearly impossible to predict.
It's certain that landslides onshore will make critical roads impassable. But underwater offshore landslides could change the shape and magnitude of the wave before it reaches land, focusing its energy and height in places no one can predict.
Liquefaction probably will occur anywhere a high water table meets loose, sandy soil. But these conditions vary from acre to acre on the Oregon Coast. The only way to know for sure is to test the soil beneath every piece of property.
Another frightening unknown involves "asperities" - parts of the plates that don't subduct evenly. Since the two plates that meet to form Cascadia aren't smooth, they won't erupt in a uniform fashion. Some pieces will shake far more violently than others, and there's no way to know where that will happen.
But the question everyone wants an answer to now is simple: When will the next big quake happen?
It will happen again, and it may happen soon. Hundreds, if not thousands, of people could die.
Throughout the past 10,000 years, scientists estimate that 19 to 21 major earthquakes have rocked the Pacific Coast via the Cascadia subduction zone, which works out to about one every 500 years. If averages were a safe way to predict earthquakes, one could simply look at the last big quake, which occurred in 1700, and figure the next one would be due in 200 years.
But earthquakes tend to occur in "clusters" of four or five. >From studying soil deposits, scientists figure that the Cascadia has experienced a cluster of four massive earthquakes during the past 1600 years.
If this is a four-quake cluster, the zone already may have entered a long quiet period of 500 to 1,000 years. But some clusters in the past 10,000 years have seen up to five events - one every 300 years. If Cascadia has one more quake left, it is due - right now.
HINTS FROM THE INDIAN OCEAN
Studying Sumatra can't answer that question. But it can help scientists know just how bad a tsunami could be here.
Andrew Moore recently returned from one of the few scientific research trips yet conducted in the region. The assistant professor of geology at Kent State University joined a team of researchers led by a scientist from the University of Tokyo.
Moore's team came across startling new information. At first, maximum wave heights on this coast had been recorded at 35 feet or less. Moore's team found heights on the open water at twice that level, and even bigger "run-up" heights - measures of the wave as it rears up after hitting land - of more than 100 feet in a few areas.
That's much higher than scientists previously had recorded in Asia or predicted for the Cascadia subduction zone. And it could mean today's inundation and evacuation maps anticipate a wave that's too small.
Moore doubts that his team's findings will alter maps significantly. There's much more research to conduct before confirming these findings.
"Science is a lot slower than people would like it to be," Moore said. "This is our first salvo in a long, long process."
Sumatra's sea floor is markedly different from Oregon's, Priest said. Here, the continental shelf reaches all the way to the fault line, so a tsunami's power is quickly diminished because it hits shallow water within seconds of its formation. The Sumatran sea floor is much deeper and steeper, giving the tsunami more room and time to gather speed, force and height.
Even if the Indian Ocean quake can't give U.S. researchers an exact glimpse of what a Cascadia event would do here, geologists like George Priest hope it will help raise awareness for people who live in earthquake country throughout the world. But he also wants that awareness to lead to more funding for more research about how tsunamis have struck in the past - and what the next one will look like. Computer models are just that - models, he knows. What a Cascadia event means for Oregon can't be known.
Until the ground starts shaking.
The Associated Press contributed to this report.
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