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Minutes after a powerful magnitude 9.0 earthquake struck off Vancouver Island one summer day, thousands of British Columbians were killed or injured by the rubble, followed by a tsunami, tremors and chaos.
Distraught survivors are crowding hospitals searching for loved ones. Roads and railway lines were damaged by the earthquake and then flooded by the tsunami. Then there are shortages of food and medical services.
A “megathrust” earthquake scenario is described in the British Columbia government's risk analysis, which estimates that more than 3,400 people will be killed and more than 10,000 injured on the day of the main shock.
“After the earthquake, thousands more people will be killed or injured by natural disasters such as tsunamis, tremors and fires,” the report says.
The scenario also describes costs of $128 billion, the destruction of 18,000 buildings and significant damage to another 10,000, while economic growth is halved and GDP and job losses are spread over the next decade. The report said the losses would exceed the combined losses of all natural disasters that have occurred in British Columbia over the past 200 years.
It said the most severe damage could be on Vancouver Island and a roughly 20-kilometre strip along coastal areas of the lower mainland, including Vancouver, stretching from the US border to the Sunshine Coast.
The analysis is part of British Columbia's Natural Hazard and Climate Risk Assessment, dated October 2025, which also outlines several other “extreme event” scenarios – severe flooding in the Fraser Valley, tidal flooding on the southwest coast after a winter storm, an urban border fire and drought that has continued in recent years.
Edwin Nissen, professor of earth and ocean sciences at the University of Victoria, said the report's estimates of fatalities and destroyed buildings were based on modeling.
“You can kind of model what an earthquake would look like and then determine how much shock it would cause,” said Nissen, who was not involved in the report.
He added that these simulations will then take into account the structural integrity of homes based on their physical location, material and building codes.
“On a purely personal level, timber-framed homes tend to be relatively safe from shaking,” he said. “If it's a brick, it's bad. If you're on a rock, if you're close to bedrock, that's good. If you're not on a rock, it's less good.”
We've all been told to prepare for the 'Big Quake' – a massive earthquake predicted to bring devastation to the Lower Mainland. Although the damage will be severe, not all parts of the region will be affected equally. Darius Mahdavi met with some of the researchers who are creating detailed maps that describe risk at a more granular level.
Nissen said the report's numbers contain a “huge amount of uncertainty” due to factors such as the time of day and year the quake occurs.
He said earthquakes can be deadlier in winter because the ground has absorbed more water, increasing the likelihood of landslides and soil liquefaction.
However, he noted that such reports are required on a regular basis.
“I think it's good that they update these emergency reports every few years because I think science moves pretty quickly. Engineering moves pretty quickly.”
The last such earthquake in the region occurred in 1700, the report said.
Nissen said researchers know about this earthquake from oral records from Indigenous peoples, as well as from recent scientific studies of the Cascadia Fault, which extends 1,000 kilometers from mid- to northern Vancouver across the Pacific Ocean to Northern California.
The report estimates the likelihood of such an extreme event to be between 2 and 10 percent over the next 30 years. It also mentions the 2004 magnitude 9.1 Indian Ocean earthquake as comparable “in terms of tectonic setting, duration of destruction and tsunami generation.”
Although 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 events in a row, 100 years apart,” he said. “In other cases, the difference can be as much as 800 years.”
The range of probabilities could be wide, he added.
“But the thing is, it could happen at any time, so we need to be prepared for it.”
Nissen also said scientists are “a little blind” when it comes to the Cascadia subduction zone because they haven't been able to record many moderate earthquakes.
“Cascadia is eerily quiet at the earthquake front,” he said.
