High up in Canada’s Yukon Territory, a seismic gun is being cocked and aimed at the little community of Dawson City—population 1,600. If a new study in the journal Geophysical Research Letters is correct, that town or one of many others in the region could be rocked by a major earthquake pretty much at any moment. The source of the danger is a 1,000 km (620 mi.) formation known as the Tintina fault that cuts northwest across the Yukon and terminates in Alaska. It has been mostly still for the past 12,000 years but appears to be getting ready to lurch to life.
“Over the past couple of decades there have been a few small earthquakes of magnitude 3 to 4 detected along the Tintina Fault, but nothing to suggest it is capable of large ruptures,” said Theron Finley, a recent PhD graduate at Canada’s University of Victoria and the lead author of the study, in a statement. That’s not the full story, though, Finley says. What the last few decades suggest and what the geological record now shows are two different things—and according to the paper, Tintina is a lot more menacing than it seems.
What caught the interest of Finley and his colleagues is a 130-km (80 mi.) segment of the fault that runs near Dawson City, with surface features suggesting that numerous large earthquakes occurred in relatively recent geological history—during the Quaternary Period, which runs from 2.6 million years ago to the present. To get a better understanding, the researchers used an existing library of high-resolution imagery from airplanes, satellites, and drones, some of them captured by lidar—which uses pulsed laser emissions to produce 3D maps of the surface. This allowed them to study that stretch of the fault in unprecedented detail—and find a number of geological secrets hiding in plain sight.
At one point in the Tintina segment, they discovered a fault scarp—or a ridged crack in the surface—where the land broke and shifted by 1,000 m (3,280 ft.). That is a clear fingerprint of an earthquake, one that, according to the rounding and wear and sloping of the scarp, occurred about 2.6 million years ago. At another spot they found another scarp, misaligned by a more modest 75 m (250 ft.), that they estimate to have been caused by a smaller but still considerable quake that occurred about 132,000 years ago. No evidence of significant quakes turned up at any time in the past 12,000 years, meaning Tintina has been relatively stable throughout the entirety of the Holocene Epoch, which runs from 11,700 years ago to the present.
But for modern day folks living in Dawson and elsewhere, that recent period of quiescence is actually bad news. Just because a fault isn’t causing quakes doesn’t mean it isn’t on the move. Finley and his colleagues estimate that Tintina is moving and accumulating strain on the order of 0.2 mm to 0.8 mm a year. Over the course of 12,000 years, those millimeters add up, and when the strain is suddenly released—which it ultimately must be—the result will not be pretty.
“We determined that future earthquakes on the Tintina fault could exceed magnitude 7.5,” said Finley in a statement. “Based on the data, we think that the fault may be at a relatively late stage of a seismic cycle, having accrued a slip deficit, or build-up of strain, of six metres [20 ft] in the last 12,000 years. If this were to be released, it would cause a significant earthquake.”
The estimated 7.5 magnitude of the quake would put it on a scale with some of history’s bigger temblors, including China’s 1976 Tangshan event which claimed an estimated 240,000 to 650,000 lives; and the 2020 Haiti quake, which killed 300,000. The Yukon Territory is much more sparsely populated than Tangshen or Haiti, meaning fewer casualties. Still, there would quite likely be deaths, along with damage to local highways, mines, and other infrastructure. The area is also prone to landslides which could be triggered by a quake.
“Our results,” the researchers wrote, “have significant implications for seismic hazard in the Yukon Territory and neighboring Alaska. If 12,000 years have elapsed since the last major earthquake, the fault may be at an advanced stage of strain accumulation.”
It is impossible to know exactly when that strain will be released, of course—one of the things that makes seismology such a confounding science. The best the scientists can do is warn locals of the long term risks and leave them to prepare go bags, survival kits, and evacuation plans. The Earth will quake at will; we can only react.