Magnitude 9.0 earthquake could eclipse all previous BC disasters: provincial report
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Minutes after a massive 9.0 magnitude earthquake hits Vancouver Island on a summer day, thousands of British Columbians are killed or injured in the debris – then comes the tsunami, aftershocks and chaos.
Distraught survivors overwhelmed hospitals as they searched for their loved ones. Road and rail links are damaged by earthquakes, then inundated by tsunami floods. There is a shortage of food and medicine.
The BC government’s risk analysis describes a “megathrust” earthquake scenario, predicting more than 3,400 deaths and more than 10,000 injuries on the day of the main shock.
It reads, “After an earthquake, thousands of people are killed or injured by hazards such as tsunami, aftershocks and fires.”
The scenario also describes a cost of $128 billion, destruction of 18,000 buildings and widespread damage to more than 10,000, while economic growth is halved and GDP and job losses soar over the next decade. The report said the damage would exceed the combined effects of all disasters experienced in BC over the past 200 years.
It said the heaviest damage could occur along a roughly 20-kilometre strip of coastal parts of the lower mainland, including Vancouver Island and Vancouver, stretching from the U.S. border to the Sunshine Coast.
The analysis is part of the BC Disaster and Climate Risk Assessment for October 2025, which also outlines several other “extreme event” scenarios – severe flooding in the Fraser Valley, high tide flooding on the southwest coast after a winter storm, an urban interface fire, and previous years of drought.
Edwin Nissen, professor of earth and ocean sciences at Victoria University, said the report’s estimates of deaths and destroyed buildings were based on simulations.
“You can kind of run a simulation to see what an earthquake would look like, and then how much ground it would shake,” said Nissen, who was not involved in the report.
He said these simulations will consider the physical condition of homes, their materials and their structural integrity based on building codes.
“On a purely individual level, wood-frame homes are generally relatively safe from shaking,” he said. “If it’s brick, it’s bad. If you’re on bedrock, if you’re close to the bedrock, it’s good. If you’re not on the bedrock, it’s less good.”
We have all been told to prepare for “The Big One” – a major earthquake that is expected to cause devastation in the Lower Mainland. Although the damage will be severe, not every part of the area will be affected in the same way. Darius Mahdavi went out with some researchers who are creating detailed mapping that outlines the risks at a more detailed level.
Nissen said the figures in the report come with a “huge amount of uncertainty” because of factors such as the time of day and year when the earthquake occurred.
He said earthquakes can be more deadly in winter because the ground has absorbed more water, increasing the likelihood of landslides and soil liquefaction.
But he said such reports are needed on a regular basis.
“I think it’s good that they update these emergency reports every few years, because I think the science moves pretty fast. The engineering moves pretty fast.”
The last comparable earthquake in the region occurred in 1700, the report said.
Nissen said researchers learned about that earthquake from First Nations oral records as well as recent scientific studies of the Cascadia Fault, which stretches 1,000 kilometers from central Vancouver through the Pacific to Northern California.
The report puts the probability of such an extreme event within the next 30 years at between two and 10 percent. It described the magnitude 9.1 earthquake that struck the Indian Ocean in 2004 as comparable “in terms of its tectonic setting, rupture length, and tsunami generation.”
While the last regional earthquake of this magnitude occurred more than 300 years ago, Nissen said they do not occur on a regular schedule.
“Sometimes, you can have two back to back, 100 years apart,” he said. “At other times, you might have a difference of 800 years.”
He said that the scope of possibilities could be huge.
“But the truth is that it could happen at any time, so we need to be prepared.”
Nissen also said that scientists are “a little blind” when it comes to the Cascadia subduction zone, as they have not been able to record many moderate earthquakes.
“Cascadia has been extremely quiet on the earthquake front,” he said.
