ROCKING THE CAPITAL
A magnitude 6.5 quake could hit, experts say
The walls start suddenly to shake and groan.
First, it’s a dull rumbling sound, like a heavy truck where no truck should be. Then comes a banging and clanging that threaten to rend the walls and the ceiling of your office.
Outside, falling plates clatter along the ground of the Sparks Street patios.
Over on Bank Street, walls bulge outward. Bricks from the older stores fall to the sidewalk and to the street.
In Sandy Hill and down in the ByWard Market, some walls of old brick homes and stores give way. The city’s oldest stone and brick churches, which have stood since the 1800s, shift ominously.
Up on Parliament Hill, the massive stone blocks tremble and overhead light fixtures rattle, but nothing collapses.
Welcome to Ottawa’s great earthquake. It’s an imagined scenario, a tale of “what if?”
But that doesn’t mean it couldn’t happen.
We know the Ottawa area could face a substantial earthquake because it has happened before: In Cornwall in 1944, when a midnight earthquake damaged hundreds of buildings; in Témiscaming in 1935; in Montreal in 1732. All these cities are part of our “seismic zone,” meaning we share common fault lines in Earth’s crust.
And none of those earthquakes was as strong as the kind capable of hitting Ottawa. The earlier three were in the range of magnitudes 5.6 to 6.2.
The quake that rattled the capital in 2010 — which was centred in Val-des-Bois, Que. — was smaller still, at 5.0.
This region, say the experts, could have an earthquake of magnitude 6.5 or so.
(Quake fact: That’s a big difference, because the magnitude scale is logarithmic: A magnitude 7 is 10 times greater than a 6, which is 10 times greater than 5, and so on.)
Of the 47 types of possible disasters on an Ontario emergency planning list, Ottawa considers earthquakes one of the five most serious threats, based on our geology and types of buildings.
That puts it on the same risk level as another ice storm, or a severe summer storm (which can bring tornadoes.)
“It really wouldn’t take much” to cause big trouble, says Pierre Poirier, the city’s chief of security and emergency management.
“An earthquake of (magnitude) 6.5 in this city could be devastating. It doesn’t have to be a 9.2.”
And the historic landslides scarring our region show that truly massive shaking has happened in the past.
So, what would happen if we had the Big One tomorrow?
Kate Ploeger was in her backyard in Orléans in June 2010 when she heard a deep rumble. Thunder, she thought. But the sky was blue. A low airplane? She couldn’t see one. Then the ground shook. Her first thought? “I’ve got data!” Ploeger studies earthquakes. In 2010, she was just beginning her PhD.
Today, she teaches at the University of Ottawa, but as a student it was her job to analyze what a big earthquake would do to central Ottawa based on the same two variables that Poirier cites: What kind of buildings are there, and what kind of ground is under them?
Ploeger knew the varying types of buildings react to shaking very differently: Unreinforced masonry, or buildings with a main structure of brick, stone or concrete blocks, do very poorly. Their walls are good at holding up weight, but they break apart when the ground shakes side-to-side. Ploeger’s survey found that 45 per cent of Ottawa’s historic core is made of these types of buildings. Outside the core, they are more rare, because modern building codes don’t allow this kind of construction anymore. Before the 1970s, however, there were no such rules. Buildings with a wood frame (even with brick on the outside) are much stronger. The wood flexes like a tree branch in the wind. “So energy (from the earthquake) is absorbed by yielding, flexing and by damaging components in the structure,” says Murat Saatcioglu, who teaches earthquake engineering at the University of Ottawa. “If it’s brittle, like brick, you can’t deform (i.e. bend) a brick. They resist forces until they fail,” and then they break apart completely. The wood structure acts a little like the shock absorber on your car, he says, with one important exception: The car’s shocks are “elastic,” meaning they spring back to their original shape. A wood-framed wall, once bent, will stay bent until you fix it. But it generally won’t fall down. California’s experiences with serious earthquakes have shown that wood-framed buildings perform well, he said. “Of course, the exterior façades came down, but I don’t think in Ottawa that the magnitude and shaking would cause failure of wood construction.” Modern office or apartment towers also do well, as their steel frames can bend without breaking. The Parliament Buildings are in a very lucky class by themselves. Saatcioglu says their location will protect them: “It is stone masonry, so it is supposed to be vulnerable, but it is sitting on a rock, so that will save it.” Call it geological good luck: The seat of government stands on bedrock, not soft soil. “If the same buildings were on soft soil, the effect would amplify,” because deep soil shakes around more than the underlying rock does. Imagine a big bowl full of Jell-O, he says. If you shake the bowl back and forth, the Jell-O wobbles and moves more than the bowl itself. If you put a tiny house from a Monopoly game on top of the Jell- O, it will be shaken more than the same tiny house in a bowl alone. Soft clay, which is all over Ottawa but especially in its eastern half, wobbles like Jell-O. The bedrock shakes only little, by comparison.
“If we had a (magnitude) 5.5 earthquake right underneath the city of Ottawa, my guess is the old brick buildings in the Market area would suffer significant damage. Newer buildings — reinforced concrete built after the 1980s — will not,” Saatcioglu said.
“In terms of single-family homes, they will be OK. The outside wall may just fall on the street, but it won’t be as critical as load-carrying members (structural pieces) coming down.” Western University’s Gail Atkinson agrees: “The real hazard in a city like Ottawa, and the same is true in Montreal, is a lot of older buildings. Think of all those old, un-reinforced masonry buildings, the old brick buildings that you see in downtown Ottawa. The ByWard Market, all of those buildings that are kind of one- to five-storey walk-up buildings.
“You might see some of those buildings collapsing.”
As a city, Ottawa depends on its bridges, both over the rivers and for highway overpasses.
Bridges, like buildings, vary in age and strength.
Older bridges, generally speaking, can experience failures of the vertical columns that hold up the “deck” — the part we drive on. But a second reason bridges can collapse is odder: The beams that hold up the deck, and which sit in turn on top of columns, may not stretch out widely enough.
Shaking can jostle them sideways until they topple over the edge of the supporting column like a coffee cup set too close to the edge of a table. If that happens, a section of bridge comes down, too.
Saatcioglu says that until Hurricane Katrina, the greatest economic damage from a natural disaster in the United States came from the collapse of bridge sections that severed Highway 5 in California, the state’s main north-south highway and an economic lifeline. That was a result of the Northridge earthquake (magnitude 6.7, plus aftershocks) back in 1994.
QUANTIFYING QUAKE RISK
“Ottawa is an area of moderate seismic hazard,” notes Claire Samson of Carleton University’s earth sciences department. “Certainly we do expect every decade or few decades to get a magnitude five-ish earthquake, like the one that was felt in 2010.”
Over a period of “hundreds to 1,000 or so years, you expect to get a really large earthquake, magnitude 6 or greater.” One very to close 1,000 years ago caused massive landslides where the Quyon River meets the Ottawa River, and about nine other landslides east along the Ottawa for 50 or 60 kilometres.
The Ottawa and St. Lawrence valleys are geologically separate, but they’re related.
The Atlantic Ocean formed once long ago, but closed up as continents shifted. Then more shifting of continents caused it to form again, says Western’s Atkinson.
The first time, “It caused a lot of deep-seated faults as the plates were torn apart. Then they all got shoved back together again and the Atlantic Ocean opened in a new place farther off to the east.”
Old, deep faults from that initial opening run along the Ottawa and St. Lawrence valleys. In addition, an old volcanic hot spot beneath the Western Quebec zone (Montreal to Témiscaming) may have further weakened the Ottawa Valley’s faults.
UNDERWATER RESEARCH
One tool for interpreting our earthquake risk is the new ability to find evidence of big quakes dating back thousands of years, or “paleoearthquakes.”
Samson works with Gregory Brooks of Natural Resources Canada, a geomorphologist who has developed a new technique. He looks underwater.
Brooks began in lakes in northwestern Quebec and has moved close to Ottawa with the technique. Working on Lac de l’Argile, or Clay Lake, north of Notre-Dame-de-laSalette.
Last summer, he and a student from Carleton did a study investigating the bottom of the lake by bouncing acoustic pulses off it. It maps the different layers on the bottom, which were laid down at different times in the past.
They found one layer where the entire lake had been disturbed.
“All around the lake, massive landslides occurred at once,” Samson said. The lake is several kilometres long. It’s still a jump to say this is proof of a major earthquake, so more field work is required, and the group also hopes to expand the project to two other lakes nearby and take sediment cores for dating and analysis. In the meantime, they are presenting their results so far to a meeting of the Canadian Geophysical Union next month.
Ploeger cautions that each earthquake is different, and that there is no one-size-fits-all estimate of the damage. It depends especially how far away the earthquake is: “Naturally, you would see more damage as you approach the epicentre,” which is the heart of the earthquake, the place where the deep rock shifts suddenly.
Nonetheless, Ploeger’s overviews offer some ideas of what damage we could expect here in Ottawa, if the Big One hit.
“You will likely have more damage in historical neighbourhoods, so ByWard Market, Sandy Hill, Centretown, Glebe. You would also likely see more damage on pockets of deep, soft clay. A deeper sediment of clay would usually amplify an earthquake wave as it approaches the surface,” making the surface shake more.
“With a (magnitude) 6.5 close to Ottawa, you would likely have some collapsed buildings.”
“You would likely see some buildings with extensive damage that is beyond repair. In some cases, it probably could be repairable,” except that the buildings around have fallen and further damaged the building that could have survived. That happened a lot in Christchurch, New Zealand (a magnitude 6.3 in 2011.)
There will be “out-of-plane failures.” This means a wall that used to be a straight vertical surface now bulges out dangerously. This happens with brick walls, and this can lead to collapse. “We’ve seen it extensive in California earthquakes (and) Christchurch.”
Even if the buildings are standing, their “guts” can be badly damaged. “You see burst pipes, gas leaks, fires within minutes after an earthquake occurring. Probably power outages, and even failures of the backup power. We’ve seen this in California, where there’s a main power failure and the backup systems weren’t adequately tied down, or designed or maintained for earthquakes.
“The other interesting one is electrical arcing and electrocution. Because you can have the wires just be dislodged a little bit and it can cause fires, or if there’s a burst water pipe and arcing then you have electrocution.”
The contents of a building can also be dangerous, “probably worse in Eastern Canada when you compare it to Western Canada” because westerners are more likely to use wall brackets or special putty to keep tall, heavy objects in place. They do this to prevent toppling in a region more prone to earthquakes than ours.
It’s not just your grandmother’s china collection that will fall.
“The other things are those huge storage racks, the floor-to-ceiling storage racks in businesses and in warehouses that can go down like dominoes.
“Chemical storage, with all the chemicals falling off shelves, whether it’s at a hardware store or a university chemistry lab. With building content, we just think it’s annoying where we have to clean up glass, but it could be HAZMAT situations.”
Roads can be blocked by debris or fires, especially in dense historical neighbourhoods where commercial buildings stand right at the edge of the sidewalk.
Bridges — even if they’re still standing — would likely be closed for inspection. Who wants to send buses across a bridge without knowing how solid it is?
The city has an overall emergency plan for all kinds of hazards, from ice storms to tornadoes.
It lays out duties and command structures for disasters, generally.
But there are separate, detailed plans for particular kinds of trouble, said Poirier, the city’s emergency management chief.
“So, the paramedic service has an emergency plan, and part of (it) is to deal with the surge in call volume.
“If there were, say, debris on the road, we would co-ordinate with Public Works to clear debris from the road. If we needed to house or shelter people, we would work with recreational, cultural and facility services to turn Nepean Sportsplex into a reception centre.
“These are the elements that all come together.”
The city’s plan lays out a complex structure of commanders, strike teams, situation units, ground support units and more. It reads a lot like this. It’s a tad ... bureaucratic.
“7.13 Emergency Operations Centre Deputy Commander
The Emergency Operations Centre Deputy Commander is responsible to support the overall management of the Emergency Operations Centre facility, assigned resources within the Emergency Operations Centre, and the provision of situation support. The Commander and Deputy Commander work together to ensure that the objectives set by the Emergency Operations Centre Control Group are implemented operationally. The Deputy Commander provides leadership for the Emergency Operations Centre Operations Group and may be delegated as Commander as required.”
The Ottawa Hospital lumps earthquakes into the general category of any incident with “mass casualties.”
The hospital explained by email that after the shaking stops, “staging areas would be set up if units were unsafe and decisions to evacuate managed accordingly.”
Depending on the severity of the event, The Ottawa Hospital would activate its Emergency Operations Centre (EOC) to assist first responders in rescue operations and to guide recovery activities. Notification is sent to staff to advise of the impacts and to stand by for deployment. To meet the capacity challenges, units would then assess current staffing levels, call back staff and plan accordingly to staff for long-term incidents.” tspears@postmedia.com