After 12,000 years of calm, a seismic outburst is brewing in northwestern Canada as an ancient geologic fault grows restless. The Tintina fault, which stretches across the Yukon Territory and terminates in the center of Alaska, has become so strained that it could unleash powerful earthquakes in the future.
A recent study published in Geophysical Research Letters explains how this ominous threat has snowballed over time, as the Tintina fault continues to show signs of buckling under pressure. Because of the sustained accumulation of strain, the fault may eventually reach a breaking point, producing future earthquakes of 7.5 magnitude or higher that could endanger Yukon cities and infrastructure.
The Tintina Fault’s History
Throughout history, the Tintina fault has been mostly dormant. The same can’t be said for a neighboring fault, the Denali fault, which was the site of a magnitude 7.9 earthquake that shook Alaska in 2002 — it turned out to be the largest inland earthquake in North America in 150 years.
The Tintina fault has only caused minor earthquakes in recent years; yet, researchers involved in the study wanted to turn the clock back and see when it was last active in ancient times.
“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 lead author Theron Finley, a recent Ph.D. graduate at the University of Victoria, in a statement. “The expanding availability of high-resolution data prompted us to re-examine the fault, looking for evidence of prehistoric earthquakes in the landscape.”
Read More: Do You Live Near an Earthquake Zone? You Might Be Surprised
The Aftermath of Ancient Earthquakes
To find evidence of ancient earthquakes along the fault, the researchers looked for fault scarps, a landscape feature caused by large and/or shallow earthquakes. Fault scarps act as records of geologic activity far into the past, although they are only a few meters wide and tall, and usually hard to find in heavily forested areas.
The researchers were able to pinpoint a series of fault scarps within 20 kilometers (about 12 miles) of Dawson City in western Yukon with the help of high-resolution topographic data and lidar surveys taken from the sky.
They found two pieces of evidence that suggest large earthquakes have occurred earlier in the Quaternary period, the current period in geologic history. First, they observed 2.6-million-year-old glacial landforms that are laterally offset across the fault scarp by 1000 meters (3280 feet). Other landforms that are 132,000 years old are laterally offset by 75 meters (about 246 feet).
This movement along the fault scraps means that the fault has slipped several times throughout the Quaternary due to earthquakes. Yet, the larger earthquakes slowed down at one point; this is evident in 12,000-year-old landforms that are not offset by the fault, indicating that no large ruptures have occurred since then.
A Ticking Geological Time Bomb
The Tintina fault, however, is poised to wake back up after all these years. The fault has a low slip rate, but it has still been accumulating strain at an average rate of 0.2 to 0.8 millimeters per year, according to the researchers. And while low-slip-rate faults produce earthquakes more sporadically, when they do happen, they tend to be particularly ferocious.
“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 meters in the last 12,000 years. If this were to be released, it would cause a significant earthquake.”
A magnitude 7.5 or greater earthquake would threaten Dawson City and also potentially cause major damage to nearby highways and mining infrastructure. In addition, an earthquake of this level would likely aggravate already unstable landslides. The researchers say the data they gathered will be integrated into Canada’s National Seismic Hazard Model to prepare for any earthquakes that may hit the Yukon in the years to come.
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Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine.
