Aftershock: Scientists drill deep beneath Pacific to study past quakes
U.S.-Canadian collaboration could clarify future hazards of Queen Charlotte-Fairweather Fault
For geologists, developing the ability to predict earthquakes is something like finding the Holy Grail — there's a chance it's impossible, but it sure would be nice.
As is so often the case, a good starting point for forecasting the future is understanding the past, and that's why a group of Canadian and American scientists recently spent 20 days on a ship off the West Coast, collecting samples from the seafloor far below.
The international team was trying to learn more about the 1,100-kilometre Queen Charlotte-Fairweather Fault, which runs from southern Haida Gwaii up to the Alaskan coast. It marks where the Pacific and North American tectonic plates meet.
Rachel Lauer, a geofluids specialist at the University of Calgary, was part of the expedition, and she's excited about the possible applications.
"Since we know there's seismic events occurring along there, understanding the hazards presented by those potential ruptures in the future and how that might impact infrastructure and development is really important," Lauer told CBC News.
The team extracted cores of sediment from the sea floor and hope that by looking at the layers of silt that have developed over time, they'll be able to determine when and where past earthquakes have happened — and how severe they were.
"It really gives us a record of, ideally, the earthquake cycle if we can time events through those cores," Lauer said.
That knowledge could help design safer pipelines, LNG plants and coastal communities in the future, she explained.
An active fault line
The fault is what's known as a strike-slip fault, a line where two plates move past each other in opposite directions. It's an exceptionally speedy fault line, according to Lauer, with the boundary moving by 55-60 millimetres every year.
That means that the Queen Charlotte-Fairweather Fault can trigger quakes and tsunamis more frequently than slower faults.
The fault was responsible for Canada's largest earthquake since 1700, the magnitude-8.1 Haida Gwaii quake of 1949, which knocked cows off their feet on the islands and caused cars to bounce around in the streets of Terrace.
It was also the source of the 7.8 that struck off Haida Gwaii in 2012, causing the hot springs in Gwaii Haanas National Park to dry up, and the 7.5 that hit a year later off the southeastern coast of Alaska.
"Even in modern history there have been significant events that were capable of generating up to six-metre tsunami waves," Lauer said.
The expedition team also used seismic-reflection surveys — a technique similar to sonar — to examine the layers of rock beneath the seafloor, and cameras to explore what lies above.
That last bit may have been the most interesting for Lauer.
"The camera work we did … identified massive chemosynthetic communities of clams and unique biological markers that suggest there are some massive mud volcanoes along this vault that we didn't know about before," she said.
The team took samples from the volcanoes' plumes, and hope to determine what they're spewing and where it's coming from.
The U.S. and Canada began teaming up to study the Queen Charlotte-Fairweather Fault two years ago, with the hope of addressing the looming threat to both countries. The fault has generated at least six major earthquakes in the last century.