Yukon earthquake reveals a fault line hidden beneath glaciers

A helicopter full of researchers with the Yukon Geological Survey is scouring a remote mountain region in southwest Yukon, looking for avalanches and landslides – evidence of a magnitude 7.0 earthquake that rattled the area last month. 

The quake, which struck near the Alaska-Yukon border on Dec. 6, has helped geologists confirm a decades-old hypothesis: it’s revealed a fault hidden beneath the earth’s surface. 

The area has been a bit of a blind spot for people like Michael West, Alaska’s state seismologist and research professor at the Alaska Earthquake Center. 

“What’s really unique about the southwestern corner of the Yukon is that two of the most massive plate boundary systems on Earth intersect at almost a right angle,” said West. “We have a limited understanding of how that works. Some people refer to this area as the ‘train wreck of plate tectonics.’” 

Both Alaska and the Yukon are seismically active places. But last month’s earthquake was in a specific area on the map, explains West, where there has not historically been significant earthquake activity – not, at least, any that has been recorded in recent decades. Many researchers have theorized that there must be a connection there between the North American plate boundary and large faults in the interior of the plate.

“It had been hypothesized since the 1960s, but we haven’t been able to directly observe it,” said Jan Dettmer, geoscience research manager with the Yukon Geological Survey. “And now we can. It’s a very significant opportunity and it certainly has international interest.” 

‘I thought my house was going to collapse’

The earthquake happened at 12:41 p.m. local time on Dec. 6, and was felt most strongly in the communities of Burwash Landing and Haines Junction, Yukon – although ground shaking was also felt as far as Whitehorse, about 250 kilometres away. 

“I was in my bedroom, and I heard my bedroom door start rattling and creaking,” recalled Pascale Dubois, who lives in a duplex in Burwash Landing. The small community is around 100 kilometres from the quake’s epicentre.

“My first thought was that it was my neighbour’s washing machine.” 

Dubois said the shock waves built in intensity until everything on her walls was swaying back and forth, and her kids began yelling for her. 

“We all ran to the living room and the whole room was swaying back and forth like we were on the ocean… it was pretty intense,” she said. “I honestly thought my house was going to collapse.”

But aside from a few items falling off walls or knocked off shelves, the earthquake had relatively little impact on people living in the Yukon.

Michael West says that’s not a reflection of its power.

“A magnitude-7 earthquake is a truly massive event. The rupture was probably on the order of 50 to 100 kilometres long,” he said. “A magnitude 7 in other parts of the world can kill 10,000 people.”

‘There’s mountain-building going on’

However, the aftermath of the earthquake is written across the slopes of a remote range in Yukon’s Kluane National Park, which is home to the tallest mountain in Canada. 

In December, researchers with the Yukon Geological Survey carried out field reconnaissance to try and look for the fault itself, and trace where and how it shook the earth. 

Dettmer says the earthquake, and the aftershocks that are still happening, will likely help reveal more about the mechanism of deformation in the area — the process by which plates collide and form mountains. 

“There’s mountain-building going on actively in this area,” said Dettmer.

West says the research interest in what happened last month is significant. 

“There are researchers all around the world investigating this earthquake in different ways,” he said. “The end product of all this is probably a new set of faults yet to be named.” 

Researchers hope mapping the fault lines beneath the ground will lead to a better understanding of the earthquakes in the area, and how much nearby communities may be at risk.