A hidden tectonic fault in Canada’s Yukon could be gearing up to unleash a major earthquake of at least magnitude 7.5, according to a new study.
The Tintina fault, which runs from northeastern British Columbia through to central Alaska, has been quietly accumulating strain for at least 12,000 years. Previously thought to be relatively benign, new analysis suggests it’s still very much active.
Worryingly, scientists can’t say when the next major quake will strike – only that it almost certainly will.
“Our findings indicate that the fault is active and continues to accumulate strain,” Dr Theron Finley, lead author of the study published in Geophysical Research Letters, told BBC Science Focus. “And so we anticipate that in the future, it will rupture again.”
Tintina is what’s known as a ‘right-lateral strike-slip fault’ – a type of fault where two blocks of the Earth’s crust slide past each other horizontally. If you stand on one side of the fault and the other side moves to your right during an earthquake, it’s called right-lateral.
Over time, one side of the fault has slipped around 430km (270mi), mostly during the Eocene period – a geological epoch that occurred roughly 56 to 33.9 million years ago – when it’s thought to have been moving as much as 13mm (0.5in) a year.
Although small earthquakes have occasionally been recorded in the region, the Tintina fault was largely considered dormant.
“There have been a few small earthquakes in the magnitude three to four range detected along or adjacent to the Tintina fault,” Finley said. “But nothing really suggests that it's capable of larger ruptures.”
That changed when Finley and his team used new technologies to re-examine the fault. Combining satellite surface models with drone-mounted Light Detection and Ranging (LIDAR) data, the researchers were able to see through the dense forest and uncover signs of a seismically active past – and future – in the Yukon.
Scattered across the landscape were fault scarps – long, narrow landforms produced when an earthquake ruptures all the way to the surface. These can stretch for tens or even hundreds of kilometres, though they’re usually only a few metres high and wide.
“In the case of the Tintina fault, the scarps appear as an interesting series of aligned mounds,” Finley said.
By dating these surface features, the researchers found that while the fault has ruptured numerous times over the past 2.6 million years, it hasn’t produced a major earthquake in the last 12,000 years – all while slowly accumulating strain at a rate of 0.2 to 0.8 mm (0.008 to 0.03 in) per year.
Fortunately, the region is sparsely populated. But when the fault does rupture, Finley warned that significant landslides, infrastructure damage, and impacts to nearby communities are likely.
“I want to be clear that we don’t have a great sense of how imminent an earthquake is,” he said. “We just know that from our observations, it appears that a long time has elapsed since the last one. But there’s not really a way to tell whether another one is more likely in the coming days and weeks versus thousands of years from now.”
Now that the fault has been confirmed as active, Finley says the next step is to better estimate how often large earthquakes occur there. While this won’t allow researchers to predict exactly when the next rupture will happen, it could provide a more reliable timescale for when one should be expected.
“Earthquakes don't necessarily occur periodically, but it would give us a better sense of how often we expect large earthquakes,” Finley said. Regardless, when Tintina finally does go, it won’t be a small one.
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About our expert
Theron Finley is a surficial geologist at the Yukon Geological Survey. He recently graduated with a PhD from the University of Victoria, Canada, where he conducted research on active faults in western Canada using remote sensing, tectonic geomorphology and paleoseismology.