Preparing for the "Big Daddy" of Earthquakes:
Vancouver's 9.0 Megathrust
THE BIG ONE: What Does It All Mean?
Megathrust events occur at the boundaries of tectonic plates, and comprise the planet's largest earthquakes and can exceed magnitudes of 9.0 and above. Examples of recent megathrust events include the 9.2 Indian Ocean earthquake in 2004, the 8.8 earthquake which struck Chile in 2010, and the 9.0 earthquake which hit Tōhoku, Japan in 2011. All were megathrust events and caused extreme destruction, economic damage and loss of life.
The Ring of Fire
British Columbia is located along the edge of the Pacific Ring of Fire, one of Earth's most tectonically active zones. 9 out of the 10 largest earthquakes on record have occurred along its edges, including the 2004 Indian Ocean, 2010 Chilean and 2011 Japan earthquakes, killing over 280,000 people and causing extreme economic, social and environmental despair.
There are no B.C. earthquakes on this list - yet - but we must prepare for what will be the most devastating natural disaster in B.C.'s history.
Global seismicity over 20 years, concentrated at plate boundaries.
Source: J Adams, 2012
Tectonic Context of Canada's West Coast
Source: J. Cassidy
The Cascadia Subduction Zone
The City of Vancouver should plan ahead for a huge Cascadia Subduction Zone megathrust earthquake.
The Cascadia Subduction Zone is a 1,300 km fault that runs underneath the west coast from Brooks Peninsula, Vancouver Island, to Cape Mendocino, California.
What used to be the Juan de Fuca plate consistently subducting (sinking) beneath the North American plate at a rate of ~4.5cm a year has now become a standstill, with the plates becoming locked together for the last 300 years.
The result? A massive megathrust earthquake. Huge amounts of pressure which, when released, will cause the North American plate to be springloaded up to as high as 14 metres west.
We’re talking about three or four or even five minutes of intense shaking,” Cassidy says. “And it’s not just one city. It’s Vancouver, Victoria, Seattle, Portland. Even high-rises in Toronto could sway.”
Watch Evelyn Roeloffs, a geophysicist working with the USGS, explain the science behind Subduction Zone megathrust earthquakes (9.0 or above) and their effect on cities such as Vancouver.
Why Vancouver?
We chose to limit our study area to the City of Vancouver for a few reasons. We hoped that by focusing on a smaller area, the resolution and detail of our data would be greater and would thus allow us to draw more insightful and applicable conclusions about the City's earthquake preparation.
With all of us being UBC students, we hold a special place in our hearts for Vancouver, and given its location in a high hazard zone on every seismic hazard map (see image on the left, from the 2010 Geological Survey of Canada), we hope that the city undertakes more projects such as this one in order to face the reality of a megathrust earthquake affecting its people, economy, and environment.