A couple walk along Whiffin Spit Park following a tsunami warning in Sooke, B.C., on Jan. 23, 2018.CHAD HIPOLITO/The Canadian Press
On Jan. 26, 1700, an estimated magnitude 9 earthquake ruptured the seafloor along the West Coast from Northern California to British Columbia. Twenty minutes later, Vancouver Island, which sits on the doorstep of the Cascadia subduction zone where the quake originated, was struck by a massive tsunami.
Evidence suggests that ocean waters sloshed up mountainsides to heights of more than 20 metres in some places, wiping away an entire swath of Indigenous settlements that dotted the island’s network of inlets.
Now, engineers and researchers have teamed up to assess the risk of a comparable event affecting those who live along the same coast today – and the results suggest that many are vulnerable.
“It’s going to happen again – maybe between now and 200 years from now – so it’s something that communities need to be thinking about,” said Soroush Kouhi, an applied science specialist with Ocean Networks Canada (ONC) at the University of Victoria, who led the research organization’s portion of the project.
The chance of a major earthquake in the region is currently pegged at about 12 per cent in the next 50 years, high enough to warrant a more detailed tsunami risk analysis, experts say.
More distant or modest earthquakes can also produce tsunamis that pose a threat. In March, 1964, for example, an earthquake off the coast of Alaska generated a tsunami that reached Vancouver Island more than three hours later. The wave was magnified by the long narrow shape of the Alberni Inlet and reached a height of six metres in Port Alberni, where it destroyed dozens of homes and other structures.
While the potential for such hazards is known, the project, which received support from municipalities and private funders, marks the first time that the risk to many communities – particularly in the northwestern portion of Vancouver Island – has been quantified in detail.
Quantifying B.C.’s tsunami risk
Nootka Sound and Esperanza Inlet on Vancouver Island are among of the areas where a detailed analysis points to a larger- than-expected risk from earthquake-generated tsunamis.
Tsunami risk
DETAIL
BRITISH
COLUMBIA
Max. wave height
0
1
2
3
4
5
6
7
Esperanza Inlet
Metres
Nootka Sound
Vancouver
Vancouver
Island
BRITISH
COLUMBIA
Victoria
Pacific Ocean
50 km
Seattle
john sopinski/the globe and mail,
source: openstreetmap; Ocean Networks Canada
Quantifying B.C.’s tsunami risk
Nootka Sound and Esperanza Inlet on Vancouver Island are among of the areas where a detailed analysis points to a larger-than-expected risk from earthquake-generated tsunamis.
Tsunami risk
DETAIL
BRITISH
COLUMBIA
Max. wave height
0
1
2
3
4
5
6
7
Esperanza Inlet
Metres
Nootka Sound
Vancouver
Vancouver
Island
BRITISH
COLUMBIA
Victoria
Pacific Ocean
50 km
Seattle
john sopinski/the globe and mail, source: openstreetmap;
Ocean Networks Canada
Quantifying B.C.’s tsunami risk
Nootka Sound and Esperanza Inlet on Vancouver Island are among of the areas where a detailed analysis points to a larger-than-expected risk from earthquake-generated tsunamis.
Tsunami risk
DETAIL
BRITISH
COLUMBIA
Max. wave height
0
1
2
3
4
5
6
7
Esperanza Inlet
Metres
Nootka Sound
Vancouver
Vancouver
Island
BRITISH
COLUMBIA
Victoria
Pacific Ocean
50 km
Seattle
john sopinski/the globe and mail, source: openstreetmap; Ocean Networks Canada
The region that was the focus of the project is home to 10 communities representing five First Nations: “These are remote communities where there have not been any previous studies,” Dr. Kouhi said.
To better understand the risk in those locations, Dr. Kouhi and his colleagues used computer models to determine the characteristics of tsunamis generated by earthquakes off the coast of Vancouver Island and also in Alaska. Based on those results, engineers with Northwest Hydraulic Consultants Ltd. in North Vancouver then created maps of flooding hazards to guide community evacuation plans.
In many places where information was lacking, additional elevation data were gathered using airplanes with lidar capability to map the details of the local landscape.
A unique aspect of the project involved gathering local knowledge from Indigenous community members, such as recollections of the 1964 tsunami and older legends of what occurred in generations past.
“We heard about tsunami canoes that were developed that could carry a large amount of people,” said Pieter Romer, Indigenous community liaison with ONC, who conducted interviews for the project. “Some would be on the shore, some further up, some would be strung together.”
The interviews were also incorporated into a documentary film that Mr. Romer produced and directed, and that is now being screened in communities around the region as part of the project’s public outreach.
Dr. Kouhi said the interviews allowed researchers to compare local knowledge with what computer models were showing, which helped refine their understanding of subsidence and other effects that have subtly changed local areas over time.
The result was a detail set of projections showing arrival times and flood patterns for earthquake-generated tsunamis, including a worst-case scenario event as occurred in 1700. The information revealed the wide range of effects that depend on local geography, which can be used to inform emergency plans and evacuation routes if a tsunami is approaching.
“There’s a six-metre difference in wave height between some areas, which speaks to the importance of investing the money necessary to get quality modelling,” said Shaun Koopman, who is Protective Services Coordinator with the Strathcona Regional District, a partner in the project.
He said evacuation plans, as a result of the effort, are being revised for four of the five First Nations that are in the study region.
Dr. Kouhi said the team investigated the effect of sea level rise owing to climate change on tsunami risks in the region. The findings suggest that while the impact on tsunamis off shore will be minimal, higher sea levels can significantly extend the zone of flooding over land.
The project addresses a key need to increase community resilience to ocean hazards worldwide, said Rebecca Martone, executive director of the Ocean Decade Collaborative Center for the Northeast Pacific – a non-governmental organization that was not involved in producing the risk assessment.
“It’s bringing the highest level of observing technology and interweaving that with Indigenous knowledge around the history of tsunamis,” she said.
The project dovetails with an earthquake warning system that ONC has developed using sensors deployed both on land and on the seafloor. The system, which is expected to become available this year, will be used to alert those who are operating critical infrastructure and who could benefit from even a minute’s worth of notice to stabilize large equipment or halt moving trains, among other actions, before the ground begins shaking at their locations.
Benoît Pirenne, the organization’s director of user engagement, said the benefit of an early warning for coastal communities is the chance to get people out of the way when a large tsunami has been triggered.
“We’re doing that in collaboration with and at the request of those communities so they can then prepare for something that we know is going to happen at some point,” he said.
Editor’s note: This story has been updated to include the engineering aspects of the project.
Ivan Semeniuk