Yukon earthquake reveals a fault line hidden beneath glaciers

A helicopter loaded with researchers from the Yukon Geological Survey searches for avalanches and landslides in a remote mountainous area in southwestern Yukon – evidence of the 7.0 magnitude earthquake that struck the region last month.

An earthquake near the Alaska-Yukon border on Dec. 6 has helped geologists confirm a decades-old hypothesis: It revealed a fault hidden beneath the Earth’s surface.

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

“The really unique thing about the southwestern corner of the Yukon is that the two most massive plate boundary systems on Earth meet almost at a right angle,” West said. “We have a limited understanding of how it works. Some people call this region the ‘train wreck of plate tectonics.'”

Alaska and Yukon are both seismically active Places. But last month’s earthquake was in a specific area on the map, West explains, where historically there has not been significant earthquake activity — at least, none has been recorded in recent decades. Many researchers have theorized that there must be a connection between the North American plate boundary and large faults in the plate interior.

“It’s been hypothesized since the 1960s, but we haven’t been able to see it directly,” said Jan Dettmer, geology research manager for the Yukon Geological Survey. “And now we can. It’s a very important opportunity and there’s certainly international interest.”

‘I thought my house was going to collapse’

earthquake struck on December 6 at 12:41 pm local time, and was felt most intensely in the communities of Burwash Landing and Haynes Junction, Yukon – although ground shaking was also felt as far away as Whitehorse, about 250 kilometers away.

“I was in my bedroom, and I heard my bedroom door slamming and creaking,” recalled Pascal Dubois, who lives in a duplex in Burwash Landing. The small community is about 100 kilometers from the epicenter.

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

Dubois said the shock waves grew more intense until everything on her walls started shaking back and forth and her children started screaming for her.

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

But other than a few objects falling off walls or off shelves, the earthquake had relatively little impact on people living in the Yukon.

Michael West says this is not a reflection of its power.

“A magnitude 7 earthquake is really a major event. The crack was probably 50 to 100 kilometers long,” he said. “In other parts of the world a magnitude 7 could kill 10,000 people.”

‘The work of building a mountain is going on there’

However, the earthquake’s consequences are etched on the slopes of a remote range in the Yukon’s Kluane National Park, home to Canada’s tallest mountain.

In December, researchers from the Yukon Geological Survey conducted field reconnaissance to locate the fault and determine where and how it moved the Earth.

Dettmer says the earthquake and the aftershocks still occurring will help reveal more about the mechanisms of deformation in the area – the process by which plates collide and form mountains.

“There is active mountain building going on in this area,” Detmer said.

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

“Researchers around the world are investigating this earthquake in different ways,” he said. “The end result of all this is probably a new set of defects that have yet to be named.”

Researchers hope that mapping the fault lines beneath the ground will lead to a better understanding of earthquakes in the area and how much danger they may pose to nearby communities.