A major defect in the Yukon in Canada has been quiet for at least 12,000 years, which could result in an earthquake of at least magnitude 7.5, new research suggests.
Based on the amount of tension that has accumulated over the past 2.6 million years, the Tintina fault is currently under stress that can lead to major tremors within human life expectancy, the researchers reported on July 15 in the Journal Geophysics Research Book. The finding may require experts to rethink the dangers of earthquakes in the area, the study authors said.
A magnitude 7.5 earthquake will threaten several small communities within the remote Yukon. However, the discovery that the Tintina fault could potentially cause such a large tremor is noteworthy, as the fault was quiet even before the end of the last ice age.
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Earth scientist Theron Finley, who conducted his research while earning his PhD from the University of Victoria in Canada, told Live Science, “those major ancient faults could remain as weak zones of the Earth’s crust and could concentrate on continuous structural strains.”
The Tintina fault covers over 620 miles (1,000 kilometers) in length and extends from northeastern British Columbia to Yukon to Alaska. At the southern tip, it is connected to a Rocky Mountain trench fault that creates a huge valley that runs through southern Canada and northern Montana.
400 million years ago, during the Eocene era, one side of the Tintina fault slid 267 miles (430 km) at a speed of about 0.5 inches (13 mm) each year. Today the faults seem quiet. In some sections, there are occasionally only small earthquakes of 3-4 size.
But “the question has always been whether it’s still a little active or is building up the strain at a slower rate,” Finley said.
To investigate, Finley and his colleagues used high-resolution satellite data and rider images from the Yukon. Lidar is a type of laser measurement that allows for accurate imaging of topography while neglecting vegetation. This is an important tool for forested areas. In this image, the researchers looked for signs on the surface of ancient earthquakes, such as a fault “cliff,” where the ground moves rapidly upwards on one side of the fault.
“These features can be hundreds of kilometers long in some cases, but only on the order of a few meters tall or a few meters wide. So you really need high resolution topographic data,” Finley said.
Researchers determined the date of each rumple in the landscape using traces left by glacial invasions that occurred at known intervals 12,000, 132,000, and 2.6 million years ago. They discovered that for over 2.6 million years, the sides of the faults migrate approximately 3,300 feet (1,000 m) from each other. Over the past 136,000 years, the opposite side of the fault has moved to approximately 250 feet (75 m). Finley said that perhaps hundreds of earthquakes need to accumulate that movement will be converted to 0.008-0.03 inches (0.2-0.8 mm) per year.
Research shows that there have been no major earthquakes that have ruptured the ground for at least 12,000 years. Researchers estimate that during that period the fault had accumulated approximately 20 feet (6 m) of accumulated strain. This is a movement that has not yet been released in an earthquake. Finley said the fault is likely broken at a strain of 3 to 33 feet (1 to 10 m) and is usually within the range where it can cause fractures.
“It could still take thousands of years for it to reach the bursting threshold, but we don’t know about it. It’s very difficult to predict,” Finley said.
It’s not surprising to learn that Alaska’s faults could be a sleeping giant, said Peter Heosler, geologist honorary in geological studies at the U.S. Geological Survey in Alaska’s U.S. Geological Survey. He said he was happy to see evidence coming out.
“It raises the risk of earthquakes on this neck of the forest a little,” he added, but it’s not that big as the area is already known to be seismically active. The obstacles are running near Dawson City, Canada, Finley said. There are also mining facilities in the area, and there is also the risk of landslides that cause earthquakes.
To better understand the risks, geoscientists need to excavate fault trenches to find rock formations that show past earthquakes and the frequency of their occurrence.
“Now we know a lot of people have happened, but how often we don’t feel,” Finley said. “Is 6 metres a lot of stocks or is there a good chance there’s a long way to go before another burst?”
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