RED ZONE: Vancouver Island's west coast is expected to be pounded with the largest waves, enormous walls of water towering up to 15 metres high at the heads of inlets.
PURPLE ZONE: Waves up to seven metres are predicted by the time the tsunami reaches the island's south end, weakening to two or three metres at Victoria harbour.
ORANGE ZONE: The Strait of Georgia, sheltered from the full force of the tsunami, can expect waves up to two metres.
First The Ground Shakes, And Then All Hell Breaks Loose
What will happen if a tsunami hits our coast: Experts say the giant waves could destroy towns, submerge forests, rip up beaches and deposit millions of tonnes of sand far inland
The Vancouver Sun
January 08 2005
By William Boei
One day, the ocean floor 100 kilometres west of Vancouver Island will rupture at a point where two of the moving plates that make up the earth's crust have been stuck since 1700.
The energy will be released all at once, the ocean floor will heave and the earth will shake for several minutes.
A tsunami will begin to spread in all directions. Then:
- Residents on the outer coast of Vancouver Island will head for high ground when the shaking stops. There is no time for evacuation warnings.
- In the quake, the island coast falls by an average of one metre, making structures more vulnerable to big waves.
- The tsunami reaches shore in 20 minutes or less.
- The sea may draw back for a few minutes, exposing ocean floor that is normally covered. Then a towering wave will thunder into the shore, only a few metres high in some places, as high as 10 to 15 metres (33 to 50 feet) in others, as it reaches shallow waters.
- Anyone on the beach or on low rocky outcrops when the waves hit is swept into the ocean.
- Beachfront homes and resorts near Tofino are swamped. Flimsier buildings are smashed.
- Hot Springs Cove, north of Tofino, is largely destroyed.
- Zeballos, a small village at sea level in a narrowing valley, suffers severe damage as residents huddle on the mountain slopes.
- At Gold River, Tahsis and Port Alice, some docks and wharves are lifted above sea level, others are permanently submerged.
- The Pacific Rim Highway is swamped where it runs close to the beach.
- The waves undermine shore lines and river banks, toppling millions of trees.
- The tsunami begins to lose energy as it rounds Vancouver Island, especially at the south end. In the northeast, the waves are still up to seven metres high when they crash into Port Hardy, Port McNeill and Alert Bay.
- In the south, Esquimalt and Victoria see waves as high as two to three metres, and Vancouver less than a metre high.
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Port Alberni knows the power
Tsunami death toll along the B.C. coast would not come close to Asia's total, experts note
The Vancouver Sun
January 08 2005
By William Boei
The outer coast of British Columbia faces the same deadly threat of tsunamis as the southeast Asian countries that were devastated in the Boxing Day catastrophe.
When -- not if -- a tsunami hits our coast, it will have the potential to smash villages into splinters, send ships, trucks and buses tumbling like Tinker Toys, submerge forests, rip up beaches and deposit millions of tonnes of sand and gravel far inland.
Here, as in Asia, anyone caught up in the avalanche of muddy water, vehicles, trees and debris from shattered buildings will be very lucky to survive.
But where the potential death toll in the Indian Ocean basin is in the hundreds of thousands, B.C. and the U.S. Pacific Northwest are likely to lose only a few thousand people and perhaps less than a thousand, a tsunami expert says.
That's no reason for complacency, warns Simon Fraser University Prof. John Clague, who specializes in natural hazard research.
Clague thinks up to a third of the victims of the Asian tsunami died needlessly for lack of a working warning and evacuation system to get them out of harm's way. The numbers here might be smaller, but the same principles apply.
And while Asian politicians were promising at a summit this week in Jakarta to implement a tsunami warning system after the fact, other vulnerable regions, including British Columbia, still have time to ensure that their systems are in working order.
B.C.'s outer coast is vulnerable to two types of tsunami: those generated by distant earthquakes in Alaska, the Aleutian Islands and Japan; and others triggered by nearby quakes off the west coast of Vancouver Island.
The difference is not in the tsunami itself -- both kinds can send waves higher than a three-storey building and hundreds of kilometres wide crashing on to the shore -- but in how much warning we get.
No early warning system will help if the quake occurs nearby. The most likely scenario involves the Juan de Fuca plate -- one of the great slabs that make up the earth's crust -- and the North American plate, which meet along a line up to 1,000 kilometres long, roughly 100 kilometres west of Vancouver Island.
The Juan de Fuca plate is subducting, or diving under, the North American plate, but the two plates have been stuck since the last major quake in January of 1700. With some of the greatest forces on Earth pushing them together, they are bending like massive springs, building immense potential energy that one day will be released all at once. The result will be a subduction earthquake of magnitude 9 or higher, comparable to or bigger than the Boxing Day quake in southeast Asia.
Like the Sumatra coast on Boxing Day, the west coast of Vancouver Island will be hit by a tsunami as soon as 15 minutes after the shaking stops -- not enough time for any warning system to analyze the threat and alert local emergency officials, let alone to organize an evacuation.
If you're on the outer coast and the ground shakes hard enough that you have trouble standing up, there is only one thing to do: head for higher ground, fast.
"You shouldn't wait to be told by the police or an emergency official," said Clague. "Turn on a radio right away, find out what's going on." And get out of there.
Bob Bugslag, director of B.C.'s Provincial Emergency Program, agreed. "People are going to have to rely on the natural warning of a severe shaking from a subduction zone earthquake, and react accordingly to ensure their safety if they live in a low-lying area.
"If you live in a vulnerable area, then you have to seek higher ground."
That's doubly true if you find yourself on the shore and notice that the water has withdrawn to an abnormal extent, exposing parts of the sea floor that are normally covered even at low tide.
Run, don't walk. Immensely high tsunami waves have equally low troughs on either side of them, and what you're seeing is the trough ahead of the first wave. If you're lucky, you have a few minutes to reach higher ground before it arrives.
Clague has been looking at pictures coming out of Sumatra now that communications are being re-established, and he's noticing how high up the trees were stripped of their leaves by the onrushing wall of water.
"It's unbelievable," he said. "It looks like the tsunami reached up to about 30 metres [100 feet] above sea level in some of those places. Holy moly."
More than 100,000 people are currently thought to have died in Sumatra, where the tsunami would have hit minutes after the quake.
But the other victims, estimated to number around 50,000, died in coastal areas of Thailand, Sri Lanka, India and even Somalia, most of them more than two hours after the earthquake, some as long as seven hours later.
"If people had been aware that this was coming and believed it and responded appropriately," Clague said, "there would have been very little loss of life, with the exception of in Sumatra."
Clague thinks a similar disaster could be waiting to happen in the Caribbean, which is also subject to great subduction quakes. The region's subduction zone follows the arc of the Antilles islands.
"It's another area that I think is underprepared," Clague said.
It's also an area of dense population clustered along low shore lines -- the same formula that proved so deadly in southeast Asia.
That illustrates a couple of the reasons fewer people will die in a tsunami here.
First, our coast is sparsely populated. From Bamfield on Vancouver Island to Bella Bella on the central coast and Masset on the Queen Charlottes Islands, the total population of the communities at risk is only about 40,000, and not all of them live on low ground.
The B.C. coast's major population centres, Vancouver and Victoria, are relatively sheltered from a tsunami.
By the time the waves hit Victoria, they are expected to be no more than two or three metres high -- enough to do damage along the shore at high tide, but unlikely to cause much if any loss of life. In the southern Strait of Georgia and at Vancouver, the tsunami will be less than a metre high -- no worse than on a windy day on the Stanley Park seawall.
Another factor in our favour is the tides. In southeast Asia, the tidal range -- the difference between high and low tides -- is minimal, Clague said, "and people build and live right at the shore line."
"That's not the case here. We have a tremendous tidal range. So people are set back [from the water] a bit more; they're not as exposed and vulnerable."
The B.C. coastline rises more steeply in most places than the extensive flatlands in the Indian Ocean tsunami zone, and so the waves won't get nearly as far inland here. As well, our buildings and other structures such as docks and bridges are much more quake- and wave-resistant than their equivalents in south Asia.
Still, we are uneasy. Tofino Mayor Allen Anderson gave voice to some of our fears when he complained that there is a gap between a tsunami warning reaching local or regional emergency officials, and word getting to the population.
Only Port Alberni, which sustained severe damage from a 1964 tsunami triggered by the great Alaska earthquake of that year, has set up a physical tsunami warning system: tall wooden poles with solar-powered loudspeakers on top, set in low-lying areas to broadcast tsunami and evacuation warnings.
All other coastal towns will depend on news media, especially radio, and on emergency personnel driving or walking from street to street and house to house to issue warnings and evacuation orders.
Tofino's concerns are not so much with the townsite, which is protected on the ocean side by Wickaninnish Island and by high embankments, as with getting warnings to the ocean-front homes and resorts that stretch along the beaches between the town and Pacific Rim National Park.
It's a different story for Cliff Pederson, the mayor of Zeballos, a seashore village of 230 people on the northwest coast of Vancouver Island.
"Tofino doesn't have that [loudspeaker system] and of course we don't have that either," Pederson said.
"And we are susceptible to a tsunami, for sure, because the town here is at sea level."
Zeballos is not only at sea level, it sits on the edge of the water at the end of a funnel-shaped ocean inlet.
Waves the size of the ones that hit Sumatra could break over the village the way a normal Pacific surf breaks over a driftwood log.
Pederson said the village has been evacuated several times during tsunami alerts, and "it's been handled quite well. We get quite a bit of warning and we don't have any trouble contacting our people."
When a tsunami warning arrives, the local emergency plan kicks in, the fire department and village council get together "and everybody gets a job to do."
Pederson estimated Zeballos could be evacuated in 60 to 90 minutes. "Normally, we'd have lots of time. We might even get three or four hours warning. Our town would be emptied out by that time."
That will work if the earthquake is in Alaska, the Aleutians or Japan, but not if it's off Vancouver Island and the tsunami arrives in 15 or 20 minutes. Pederson knows that would be trouble, and residents will have to figure out what's happening and save themselves.
"We live in a very low, narrow valley," he said. "If we had a major earthquake I don't know what would happen to the community, because we're surrounded by mountains on both sides."
Clague said the final part of the tsunami warning system, getting warnings and evacuation orders directly to residents, has to be in place.
"That's critical," he said. "If there's a break in that link, then it's pointless. The whole system breaks down."
Bugslag has been inundated with questions about how ready B.C. is for a tsunami. His answer is that in light of the south Asian quake, the Provincial Emergency Program will hold a series of workshops with coastal communities to identify the gaps in existing provincial and local tsunami response plans, starting before the end of January.
"Any time you have an event like this where there's lessons learned is a time to go back and re-evaluate the planning process, engage the citizens and identify those gaps and try to determine ways to mitigate those gaps," he said.
The province's overall tsunami plan, which counts on local plans activated by local emergency program coordinators and RCMP detachments to get warnings out to the public, was last revised in 2001. "You'll probably see a full revision of that plan in the fall of this year," Bugslag said. "Then we'll test it and exercise it based on the new information."
The Asian quake and tsunami could spark the biggest flurry of interest in earthquake preparedness in B.C. since the 1980s, when scientists first began to pinpoint how big our offshore subduction quakes could be, and how often they might occur.
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Scientists dig out day, time, size of past earthquakes
The Vancouver Sun
January 08 2005
By William Boei
We know now that the last big subduction quake off Vancouver Island occurred at 9 p.m. on Jan. 26, 1700, with a magnitude of at least 9 -- the same as the Boxing Day quake or higher.
We know that much detail because undersea subduction quakes invariably set off tsunamis, and scientists have been digging into the deposits of sand and gravel that tsunamis dump on the shore, sometimes as far as four or five kilometres inland.
Carbon dating determines the age of deposits within 50 to 100 years. One site contains seven distinct layers of deposits over a 3,500-year period, and another shows 14 tsunami events over 7,000 years.
Unfortunately they are not evenly spaced, Simon Fraser University earth sciences Prof. John Clague said. Subduction quakes off Vancouver Island have occurred as far apart as 1,000 years, and as close together as 100 years.
"So we can't say when the next one will be," Clague said. "What it does tell us is that it's not just a one-off. It's part of the normal geological environment in the Pacific."
The 1700 quake produced a tsunami that crossed the Pacific Ocean and did considerable damage in Japan, where written records were kept of the time and size of the waves. Using that and studying sand and gravel deposits left by the tsunami in Japan, scientists were able to calculate the exact time of the earthquake and estimate its magnitude.
What makes tsunamis so powerful is that they are "amazingly efficient" at capturing and transmitting the immense amount of energy released by a quake.
"The energy is generated by the earthquake and it's transmitted into a wave form," Clague said.
"And once the waves begin to move, they lose very little energy. So they can travel hundreds of kilometres and then once they reach the shore, transmit that energy into running up on to the shore."
Spectacular as they are, however, they are not B.C.'s biggest earthquake problem.
"I try to reassure people that this is a terrible threat, but it's a much lesser threat to our main population centres," Clague said.
"We tend to be mesmerized by these huge earthquakes. But often, as in the case of Kobe, there are much smaller earthquakes that are very devastating."
Kobe, Japan, was hit in 1995 by a shallow non-subduction earthquake of magnitude 7.2, similar to the quakes to which southern B.C. is subject. It was immensely destructive, killing 5,100 people and causing immense direct and economic damage.
For every great subduction quake, B.C. gets 10 to 20 quakes of magnitude 7 to 7.5, Clague said, and while not all of them strike populated areas, when they do they can be very destructive.
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