Alexander Cruden, chair of the geology department at the University of Toronto, is searching for the right analogy, the apt metaphor. He finds it in the ballroom.
"Basically all of the plates, they're in a delicate balance," he says. "They're dancing with each other."
Earthquakes, like the magnitude 7.0 one that devastated Haiti last week, are what happen when that slow yet powerful choreography of tectonic plates falters.
And they're far more common, even in Ontario, than most people likely imagine. It's just that, with rare exception, they're barely strong enough to be felt, let alone cause damage.
Around the world, there are nine major plates jostling with one another. They're basically the foundation of the earth's crust and the uppermost mantle underneath, collectively dubbed the lithosphere.
But there are also dozens of smaller plates and platelets, such as the Juan de Fuca Plate on Canada's west coast, sandwiched between the giant North American and Pacific plates. So the dance can get complicated.
The quake in Haiti, for instance, occurred along part of the Enriquillo-Plantain Garden Fault, which runs East-West through Haiti to the Dominican Republic in the east and Jamaica in the west.
It's a so-called "strike-slip" fault, meaning the plates on either side are sliding in opposite directions.
In this case, the Caribbean Plate south of the fault line is moving east, while the small Gonvave Platelet on the north side is sliding west.
All that grinding movement creates a lot of stress and, when it becomes unbalanced, gets released in the form of earthquakes.
That's why Canada's biggest worries are in British Columbia, where the Juan de Fuca Plate is part of a much bigger system that includes the Queen Charlotte Fault to the north and the San Andreas Fault in California.
While the biggest earthquakes tend to occur where along the faults separating the plates, they also regularly happen much farther afield, which is where Ontario comes in.
Most quakes in eastern Canada are small, between the magnitudes of 1 and 5. (Earthquakes are measured by on a logarithmic scale, so a magnitude 7 such as the one in Haiti is 10 times stronger than a magnitude 6, and 100 times greater than a magnitude 5.)
Why Ontario? "There's not a lot of agreement on what causes them," says Cruden, by which he means no scientifically precise explanation.
But some of the broad factors are known, and the first is the Mid-Atlantic Ridge that separates the African and Eurasian plates from the North American Plate, which they're slowly pushing to the west and southwest.
Some of the stress from that travels through the North American Plate, causing so-called intra-plate earthquakes when that stress builds up around some smaller geological structures or weaker parts of the overall plate.
In this, there are three main candidates in eastern Canada, all of them more or less connected.
There's the Ottawa Graben, an ancient valley running along the Ottawa River, which was created when the Earth's crust dipped between two fault zones. At its eastern end, it joins up with St. Lawrence Rift, a half-graben, which then parallels the river to the Saguenay Graben.
One of the biggest earthquakes to hit eastern North America in the past century, in fact, was the Saguenay earthquake of 1988, which measured 5.9.
But some of the stress buildup in this part of the world does have a more domestic origin: the glaciers.
When they covered Ontario 12,000 years ago, the weight of all that ice, three-kilometres thick, literally pushed the Earth's crust down. "The surface has been rebounding up to its original level ever since," says Cruden.
You can see it in the so-called "pop-ups," or unexpected hills in farm fields, which likely occurred relatively soon after the glaciers retreated.
Yet the most dramatic examples may well be Toronto ravines, which were largely formed by the earth rising on either side of them.
Happily, notes Cruden, "We're in the tail-end of that uplift."
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Scientists: Haiti must prepare for more massive quakes
by Mira Oberman Mira Oberman – Sat Jan 16, 2:04 pm ET
CHICAGO (AFP) – Haiti and its neighbors must prepare themselves for more massive quakes after the devastating tremors this week increased pressure along a lengthy fault line, scientists warned Friday.
Paul Mann, a senior research scientist at the Institute for Geophysics at the University of Texas at Austin, warned that just because the rebuilding process had started people shouldn't assume the risk was over.
"This relief of stress along this area near Port-au-Prince may have actually increased stress in the adjacent segments on the fault," he told AFP.
Researchers have already begun to work on models to try to predict how the stress changes resulting from the 7.0-magnitude quake which struck Tuesday is affecting the adjacent segments of the fault.
"This fault system is hundreds of kilometers long and the segment that ruptured to form this ear quake is only 80 kilometers long," Mann said in a telephone interview.
"There are many more segments which are building up strain where there haven't been earthquakes for hundreds of years.
"Potentially any one of these segments could cause an earthquake similar to that which happened in Haiti."
There are, thankfully, only two major population centers along the fault: Port-au-Prince and Kingston, Jamaica.
But as demonstrated in the chaos which followed Tuesday's tremor, the impact of a quake of that magnitude can be "paralyzing," Mann said.
Adding to the danger is the fact that the segment which broke was not among those closest to Port-au-Prince.
And there is a second fault system in the north of Haiti which extends to the Dominican Republic which has not ruptured in 800 years and has built up sufficient pressure for a 7.5 magnitude quake.
"The question is when are those going to rupture," Mann said, adding that it is very difficult to predict "whether or not that's going to happen next week or 100 years."
Eric Calais, a French geophysicist who works at Purdue University in Indiana, is among those trying to assess the danger.
He had warned Haitian officials years ago of dangerous pressure in the fault which caused this week's devastating quake, but little could be done to reinforce the desperately poor nation's weak buildings.
"The Haitian government is not to blame in this," Calais told AFP.
"They listened to us carefully and they knew what the hazard was. They were very concerned about it and they were taking steps. But it just happened too early."
Calais began researching the fault line in 2003 and soon took his initial findings to the Haitian government, even meeting with the prime minister.
In March 2008 he and Mann presented a paper showing that the fault had built up sufficient pressure to cause a 7.2 magnitude quake.
But they could not pinpoint when the quake might strike and the government was occupied with recovering from a series of four hurricanes which struck that year.
While the government had begun work on an emergency response plan, little could be done to retrofit and strengthen key buildings such as hospitals, schools and government buildings from which rescue operations could be organized.
"It's a poor country," Calais said. "Strengthening a building to resist a large earthquake can be as costly as replacing the building."
The devastation will allow Haiti to rebuild stronger than before, Calais said, noting that there are relatively cheap engineering solutions that can be applied to ensure that new buildings will not collapse in the next quake.
"It's very important for Port-au-Prince to rebuild properly," he added. "There are other segments of that fault that could rupture in the future."
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