Initially, it is necessary to distinguish between seismic hazard and seismic risks. Seismic hazard is the possibility that an earthquake of a certain level will occur at a given location. In this regard, British Columbia, particularly Vancouver, is the region most likely to experience very, very large earthquakes due to the existence of large faults in the geology of Western Canada.
There are no such faults in Quebec, but earthquakes still occur regularly. We know, for example, that the Charlevoix region was already hit by a very strong earthquake in the 17th century. [Editor’s note: the Charlevoix seismic zone has experienced at least five earthquakes with a magnitude greater than 6.0 over the last four centuries.]
However, the surface area exposed during an earthquake is greater in the East than in the West. An earthquake in Charlevoix will be felt as far away as New York, while in the West, you no longer feel anything after a hundred kilometers.
Risk is the product of hazard and the possibility of human and economic losses. The city with the highest risk in Canada is obviously Vancouver. But the one that comes in second place is Montreal, because it is a big city, with a huge population and buildings, and whose hazard is not negligible. If we take these two factors into account, this results in a very high seismic risk.
The Geological Survey of Canada is responsible for assessing seismic hazard across the country and updates its data almost every five years. The latest edition dates back to just 2020 with new knowledge and new modeling.
Data from the Geological Survey of Canada is considered in what is called the National Building Code of Canada. It is a model code that is adopted by each province. The latest Quebec Building Code dates from 2015 and, therefore, does not take into account data from 2020. On the other hand, most consulting engineering offices will use the most recent editions of the code and standards of Canada.
This code tells engineers the forces to apply to structures so that they resist an earthquake. There are standards for concrete, steel, masonry structures, etc. Any major building must comply with these standards and, therefore, must be sized taking into account the seismic hazard. These standards are higher for important buildings that absolutely must continue to operate in the event of an earthquake, such as hospitals.
Standards were developed in the United States following the Great San Francisco Earthquake of 1906. Canada followed in the 1930s and 1940s, but the knowledge was not adequate. At the time, we did not know dynamic calculation or the dynamic behavior of buildings. We treated the earthquake like the wind, but the loads were clearly too low.
We can truly speak of a modern seismic code and standards from the 1970s. Since that time, research conducted in Canada, the United States, Europe, Japan, all over the world, has allowed us to develop construction methods that have improved to the present day.
The buildings were built with inappropriate standards. The good news is that as soon as a building changes its purpose, for example a factory converted into an apartment building, the building must be updated with the new construction standards. This is required by law.
Of course, there are a variety of methods that can be used to improve earthquake resistance. This is not a problem, we know these methods applied throughout the world. There are ways to improve steel, concrete or masonry buildings. Even historic and heritage buildings need to be updated according to new building codes.
It is essential to consult a structural engineer. An engineer must evaluate the planned changes and ensure by calculation that the project is safe.
Avoid collapse. This is the main rule that governs us. No collapse, no loss of life. The building may suffer very significant damage. The structure may be replaced or destroyed, but we do not want there to be a collapse and a loss of human life. This is the number one rule of every structural engineer.
