What are the risks of earthquakes in Quebec?
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.e century. [NDLR : la zone sismique de Charlevoix a connu au moins cinq séismes d’une magnitude supérieure à 6,0 au cours des quatre derniers siècles.]
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.
PHOTO PROVIDED BY THE UNIVERSITY OF SHERBROOKE
Patrick Paultre, holder of the research chair in structural dynamics at the University of Sherbrooke
What is the difference with seismic risk?
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 large 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.
Are our buildings built as a result of this hazard?
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 be applied to structures so that they can resist an earthquake. There are standards for concrete, steel, masonry, etc. structures. Any important 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.
When did seismic standards begin?
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 carried out 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.
However, a large part of Montreal was built before 1970. Can we improve the seismic capabilities of a building?
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 to an apartment building, the building must be updated with the new construction standards. This is required by law.
So there are ways to improve a building’s resistance to earthquakes?
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.
What advice can we give to owners of small, century-old plexes in Montreal who are knocking down walls to afford large open rooms?
It is essential to consult a structural engineer. An engineer must evaluate the planned changes and ensure by calculation that the project is safe.
In conclusion, what is the main quality of seismic architecture?
Avoid collapse. This is the main rule that guides 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.