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Heritage at stake in earthquakes
The West Coast’s geology shows drowned marshlands and forests that submerged during a magnitude 9 earthquake 300 years ago. It also shows 13 significant earthquakes have occurred in the last 6,000 years.
“In a typical year we have three or four earthquakes that will be felt by somebody around Victoria,” says Garry Rogers, a senior research scientist for the Geological Survey of Canada, Natural Resources Canada and an adjunct professor for the School of Earth and Ocean Sciences, University of Victoria.
Not only are we living in an area where subduction quakes, like the one that occurred in 1700, we are also in a zone that includes crustal quakes.
“There’s absolutely no way you can predict earthquakes, that’s fact No. 1,” Rogers says.
Instead, what Rogers and his co-workers at the Geological Survey of Canada do is try to understand where earthquakes will hit, their effects and how to minimize the damage.
Their research ends up in the model building code put out by the National Research Council.
The thing that always fails is un-reinforced masonry, Rogers explains.
“Here, our vulnerable structures are old brick buildings that haven’t been reinforced. Some of the ones downtown have been reinforced and some of them haven’t. Christchurch is a good example of that. Those that had some kind of retrofitting survived … and they lost a lot of valuable heritage buildings.”
A magnitude 6.7 earthquake in Christchurch, New Zealand in 2011 killed 185 people. The city, which is similar to Victoria in population and type of building construction, will continue to rebuild for years.
“If you’re really concerned with heritage buildings … you need to convince as many people as you can that you should retrofit them and make them earthquake resistant,” Rogers says.
After an earthquake the City of Victoria follows a process that first makes sure lives are not at risk, it then moves on to “rapid damage assessment which determines which buildings are safe to enter, that process can take weeks, says Rob Johns, emergency co-ordinator for the Victoria Emergency Management Agency.
“We have a list of heritage buildings, both residential and non-residential, in the city. Not every one has an accurate floor plan,” Johns says. “Many of the heritage features have been catalogued, many have photographic records.”
Johns says many of our buildings are vulnerable to earthquake damage and there is always room for improvement, not only here but across North America.
“Even if you don’t (retrofit) because it costs money, you should document structures and what their heritage significance is and have the building plans on hand so that when you have the earthquake and the building is partially damaged, you don’t have some fire chief saying ‘let’s just tear it down,’” Rogers says.