After a devastating hurricane season for people in and around the
Imagine that the building you’re in begins to shake violently. Shelves topple; windows shatter; gas, sewage and water pipes rupture; electrical wires snap; the entire structure sinks several feet into the ground, sending it toppling onto its side, as a mass of water rushes into the streets and buildings around, creating a toxic cocktail of industrial contaminants, human waste and decomposing bodies.
These are just some of the possibilities that students and staff at Kwantlen’s
But there is some good news for Kwantlenites. The
Still, there are many good reasons for concern, according to experts in the field, such as Kwantlen’s own John Martin, a geology instructor at the
Liquefaction involves water-saturated sediments acting like a slushy mixture when shaken, he said.
“If the ground material starts to shake, it will behave like a liquid and any buildings that are on it will start to sink,” Martin explained. Perhaps even the dykes are going to collapse or settle, which could lead to flooding by tidal movements or, more likely, river water.
According to an engineering website from the
In a telephone interview with The Chronicle, John Clague — director of the Centre for Natural Hazard Research, geology professor at
"Picture this loose sand, and you’ve got all this water in the pore spaces,” said Clague. While the sand grains are relatively motionless, they’re in contact with one another and maintain an overall rigidity. As this sand is shaken, the grains lose contact and become suspended in their pore water. When this happens to soil, such as that found in
However, those grains will not become suspended in their pore water where the sand is packed to a certain density, he added.
The fact that liquefaction is a problem facing buildings in
Clint Low, a structural engineer from Bush, Bohlman & Partners, who oversaw the designing and construction stages of Kwantlen’s Richmond campus, said a densification process was used to solidify the ground by forcing water out from the sediments beneath the construction site; a 10-tonne steel disc was hoisted into the air by a crane and pounded into the ground repeatedly for several months.
“The building now just sits on pad footing,” said Low. Pads have been placed under each of the campus’s supporting columns. This displaces the weight of the building over a larger area than the columns alone, which have a smaller diameter.
Previous to this, the site was loaded with a small mountain of sand to densify the ground and force out even more water from beneath the construction zone, said Low.
According to building plans for the campus, made available to The Chronicle by the city of
Considering Clague’s remarks about densely packed sediments withstanding the tendency to liquefy, Kwantlen appears to be on pretty solid ground.
“It depends upon the characteristics of the ground and how intense the shaking is as to how deep these sediments would liquefy,” explained Clague. “Roughly speaking, we’re talking about 10 or 15 metres.”
Engineering tests are fairly accurate when predicting the depth where sediments are not at a reasonable risk for liquefaction, he noted. “But of course, there’s extreme events that are off the scale where those engineering measures still wouldn’t work.”
The chance an extreme event like that will occur in close proximity to
“You can only spend so much money,” said Clague. There’s a balance between the cost of protection and the probability of damage from a future earthquake.
Determining the probabilities of a future earthquake isn’t so easy, mind you.
There are basically two types of earthquakes that the Lower Mainland could experience, said Clague: the big one and the small one.
The big one will occur when the Cascadia Subduction Zone slips along a large section of its two converging plates, just off the coast of
Determining the probability that the big one will ever occur is relatively easy, because the subduction zone is so obvious. Determining exactly when it will happen is next to impossible.
Evidence suggests that these earthquakes take place about 100 to 1000 years apart, due to one plate, the Juan de Fuca, diving down under the other, the North American, Clague explained.
“Essentially, where those two plates are in contact, there’s a huge geologic fault,” said Clague. “It’s one of the largest you get on earth.”
It’s thought that a locked portion of that fault is accumulating a huge amount of strain, which will eventually be released during an earthquake, he said.
What’ll make the big one so big is that this fault will likely rupture over a very large area, producing a huge amount of shaking that could last for minutes, said Clague. The longer the shaking, the worse off
The one thing
Despite being about 150 kilometres away from where the rupture will likely occur, the downside is that it’s going to be such a large release of energy that
A magnitude 8 earthquake has a radius of damage that’s hundreds of kilometres, said Clague, whereas that of a magnitude 6 extends only about 30 kilometres.
The worst case scenario, however, is not the big one off the coast of Vancouver Island, but rather a smaller earthquake with magnitude 7 or 7.5 in close proximity to the Lower Mainland, said Clague.
Though none are known to be in the Lower Mainland area, non-subduction zone fault lines can lie hidden virtually anywhere. These are unlikely to ever cause a magnitude 9 earthquake, but they can be the source of a magnitude 7, which is essentially more common in the grand scheme of things, said Clague.
These smaller earthquakes occur on fault lines such as those that cut across the North American crustal plate, which is basically
If a magnitude 7 earthquake has an epicentre within 20 kilometres of
“It would be truly catastrophic,” he said. “There would be, probably, over $100 billion damage.”
No one knows for sure if this can happen in the Lower Mainland, though. “Unfortunately that’s a weak link in our knowledge,” said Clague.
Geologists know where a lot of faults are, but most faults are dead. The challenge is recognizing the faults that can potentially produce earthquakes.
“We’re working on that,” he said. “There’s been a number of what we call capable faults — faults that can produce big earthquakes — that have been recognized, mainly south of the boarder.”
Recently, one of these hidden faults was identified about 10 kilometres south of the boarder, near Deming, Wash., which is close enough that Lower Mainland communities could experience damage, said Clague.
As for closer to home, Clague said “there are, undoubtedly, faults around here that can produce earthquakes. The problem is identifying them.”
One of the keys to identifying these hidden faults is in technology called LIDAR (Light Detection and Ranging), which makes it possible to take air photos of an area and strip away the vegetation to see a simulated image of the ground surface below. This makes it easy to identify potential fault locations, which can then be examined by ground teams to verify if it’s actually a fault or not.
As simple as it sounds, LIDAR surveys are expensive. With a price tag that can reach into the millions, “municipal governments don’t typically want to invest that kind of money,” said Clague.
“Right now it’s like hunting for needle in a haystack,” he said. “Unless you have some targets, you can’t go out and look at them and see what their history is.”
Aside from big ones and small ones, perhaps the most problematic aspect of an earthquake for people in
The dykes surrounding the island are not designed for earthquakes, said Clague.
“The worst case scenario would be if the dykes failed during the freshet in July,” said Clague, referring to the seasonal thaw that sends a sudden surge of water down the
“That would be bad news,” he said. “At very high flows, it’s definitely above the level of the surrounding plane, so if you had a breech under those conditions you’d have a tremendous amount of water flooding in.”
Another common concern for
According to Clague, who recently finished a study commissioned by the city of
“We looked to see if there was any evidence in geologic record for tsunamis, and there’s none,” he said. “Going back thousands of years we don’t think there’s been a tsunami,” or at least one large enough to be of concern.
Of course there’s always the worst case scenario where the unexpected can happen, he said.
For example, if the tides are high when a tsunami occurs, and liquefaction causes sections of the seafront dike to disintegrate, then there’s a possibility for a tsunami to cause some damage, he suggested, though this has a very low probability of happening.
With such a wet outlook for Richmond in the event of a major earthquake, Kwantlen student Shira Osipo said she’s aware the campus is in dangerous spot.
“We’re due any day for a really big earthquake,” she said. “It’s kind of freaky.”
Osipo tries not to think about the possibilities because the thought alone is scary enough, she said. She expects the dykes to burst and major flooding to cause havoc.
The city and Kwantlen need to tell people what to expect, how to prepare themselves and where to go if major flood is to occur, said Osipo.
Another Kwantlen student, Jessica Munn, said she was also concerned about the possibility that an earthquake will cause flooding in Richmond.
“The dyke won’t hold,” she said, “and the river will pour in.”
Though she has other reasons, Munn said the threat of an earthquake is partly why she wants to move out of Richmond to “somewhere higher up.”
Regardless of her concern for where she lives, Munn said she has no problem studying at the Richmond campus, which to her seems like a well designed structure.
Other than the windows in the front hall that could fall down on students below, she said “it’s probably pretty safe for the most part; it’s all brick and steel.”
Despite all the dangerous possibilities, Munn notes that “there’s nothing to say there will or won’t be an earthquake anytime soon.”