On Monday May 1, 2017, at around 5:30 a.m., a magnitude 6.2 earthquake landed near the B.C.-Yukon border, followed by another slightly stronger one at around 7:30 a.m. The rare event got a lot more people talking about seismic activity in the region, and a few murmured their fears of an eventual “big one.”
While this train of thought is understandable (if a bit pessimistic) in places like Vancouver Island and California (seen as overdue for some major quakes), the Yukon’s situation isn’t quite the same.
Maurice Colpron, head of Bedrock Geology at the Yukon Geological Survey, is a leading expert on the geology of the northern Cordilleran mountain belt. He said that May 1, 2017, was a unique event and broke down how earthquakes affect the Yukon.
“I do recommend that we all be prepared to be self-sufficient for seventy-two hours, in case of emergency, but I’m not talking about houses falling down or anything like that,” said Colpron. He said that damage to infrastructure, causing power outages and road blocks, is more of a concern.
Hotspots for seismic activity in the Yukon
Seismic or earthquake activity in the Yukon occurs primarily in southwest Yukon, from the Denali fault to the Gulf of Alaska. The largest-magnitude quakes mostly occur there, including those from May 1, 2017.
“Yukon earthquakes are predominantly shallow, generally low-magnitude strike-slip earthquakes,” said Colpron. He said that these larger quakes occurred mostly along strike-slip faults that are linked to the plate boundary between the Pacific and North American plates.
Yukon communities that are most at risk of earthquake hazards are those closest to what Colpron describes as the “hotspot of activity” in southwest Yukon, and particularly those located near the Denali fault—Haines Junction, Burwash Landing and Destruction Bay are closest to the fault. Beaver Creek is also relatively close to the Denali fault.
“The Denali fault system experiences multiple low-magnitude events every year,” Colpron said. “Although the Alaska portion of the Denali has experienced more and larger events than its Yukon portion, we can’t preclude the possibility of large events in Yukon. Infrastructure closest to epicentre [is] most likely to be damaged by ground motion.”
The potential destructive forces or ground motions of an earthquake decrease rapidly away from epicentre. Even though, Colpron points out, “we might experience a good shaking,” as was the case on May 1, 2017.
“Of course, the main infrastructure that could be affected by earthquakes are roads following the Denali fault corridor in western Yukon—the Alaska Highway and the Haines Road.”
The actual plate boundary is located along the Fairweather-Contact faults in this region (extension of the Queen Charlotte fault to the south).
Clusters of mostly low-magnitude earthquakes north of the Tintina fault, in the Ogilvie, Richardson and Mackenzie mountains, in central Yukon, are not as well understood. “Current thoughts are that they are far-field effects of collision of the Yakutat terrane in the corner of the Gulf of Alaska,” said Colpron.
The Yakutat terrane is a piece of crust carried along the Queen Charlotte-Fairweather fault system that Colpron said is being “stuffed” underneath the St. Elias Mountains, explaining their rapid rise and extreme elevation.
“The current hypothesis is that much of Yukon is gliding slowly to the northeast along deep faults that come to surface in the Richardson–Mackenzie mountains, 600–700 kilometres away from the ‘collision’ of these tectonic plates.”
Pulse of the planet
While many find earthquakes and the accompanying ground tremors scary, not to mention the occasional disruption of human activity and infrastructure, Colpron sees them as mostly a good thing. “We live on a dynamic planet. The tectonic plates are constantly in motion—new ocean floor is being created at mid-ocean ridges and consumed at subduction zones where it returns into the mantle,” he said.
He pointed out that these movements are healthy and normal functions of the Earth’s natural rhythm. “The Earth is constantly reshaping itself as the tectonic plates grind past each other or bump into each other, and this activity generates earthquakes, particularly near plate boundaries.”
Colpron said that, in a way, this constant reshaping and the close interactions between plates (the lithosphere to geologists) and the atmosphere and ocean can metaphorically suggest that the “planet is alive …” and, he said, “… in this sense, earthquakes are kind of the heartbeat of the planet … so if she’s shaking, the planet is doing fine.”
It’s always good to know where you stand, and the same can be said for earthquake preparedness strategies.
Colpron explains that the Yukon is located in the mountainous northern Cordillera region, which was developed along the western edge of the North American continent, near its boundary with the Pacific Ocean (or tectonic plate).
“Earthquakes occur mainly along tectonic plate boundaries. They are a fact of living in western Canada. That being said, most earthquakes are generally of low magnitude, and only a few are usually detected by people.”
Although southwest Yukon is along the plate boundary, Colpron said the region has historically experienced fewer numbers of quakes and generally of lesser magnitude than Alaska.
“The chance of a large earthquake near Whitehorse, where most of us live, is very low. We only have one small event of M2.6 recorded within thirty kilometres of the city in the past fifty years.”
Colpron wanted to clarify that, while we can always guess, scientists cannot predict earthquakes and that claims to the contrary should be taken with a grain of salt. “We can only study past events and essentially guess that future events may resemble the past …” He gave an example: “We know from studies on Vancouver Island that the Cascadia Subduction Zone experienced a major quake every 300–500 years, with the last major event on January 26, 1700.
“So it’s fair to say that the Vancouver–Pacific Northwest region is probably due for another ‘big one,’ but who’s to say when it will occur … could be in 200 yrs? or tomorrow? Not much of a prediction really …”
Fore those of you yearning for more, an earthquake awareness campaign takes place every year on October 18 at 10:18 a.m. (www.shakeout.org/yukon/).
The website provides info on how to protect yourself in case of severe ground motion. “Other preparations for emergencies, such as earthquakes, are the same as any other emergencies, such as wild fires or floods,” said Colpron.
“The basic rule—you should be ready for self-subsistence for at least 72 hours …”
Yukon government provides information and guidelines for emergency preparedness at PreparedYukon.ca.