Ancient Canadian fault could produce major earthquakes in the future
Researchers found high-resolution evidence of a future earthquake threat.
The Tintina, a major geologic fault that extends 1,000 km northwestward across much of the Yukon Territory, was thought to have been inactive for at least 40 million years, but new research led by a team at the University of Victoria (UVic) finds evidence of “numerous large earthquakes”, suggesting additional earthquakes could occur in the future.
The team used high-resolution images from satellites, airplanes, and drones. They found a 130-km-long fault segment near Dawson City, suggesting seismic activity in the Quaternary Period, dating from 2.6 million years ago to today.
"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," Theron Finley, recent UVic PhD graduate and lead author of the recent article, says 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."
Canada’s current understanding of earthquake frequency and risk is limited to the last couple of hundred years, the authors say, and it is comprised of data derived from Indigenous records, historical archives, and modern technology.
“However, for many active faults, thousands of years can elapse between large ruptures,” the authors say in a statement.
Large or shallow quakes can rupture Earth’s surface, creating a linear feature in the land known as a fault scrap. This feature, which can be hundreds of kilometres long, can remain for tens of thousands of years and provide insight into seismic activity in the area. They’re notoriously difficult to detect, especially in Canada’s dense forests.
The high-resolution topographic data used in the study is one of the best ways to detect fault scraps.
It revealed glacial landforms that formed about 2.6 million years ago were laterally offset across a fault scrap by 1000 metres. Some that are 132,000 years old are offset by 75 metres.
“These findings confirm that the fault has slipped in multiple earthquakes throughout the Quaternary period, likely slipping several meters in each event. What's more, landforms known to be 12,000 years old are not offset by the fault, indicating no large ruptures have occurred since that time. The fault continues to accumulate strain at an average rate of 0.2 to 0.8 millimetres per year, and therefore poses a future earthquake threat,” the authors write in a statement.
Finley says future earthquakes on the Tintina fault could be major, exceeding a mangitude 7.5, potentially causing severe shaking in Dawson City, a community with a population of about 2,350 people.
“Compounding the hazard from seismic shaking, the region is prone to landslides, which could be seismically triggered. The Moosehide landslide immediately north of Dawson City and the newly discovered Sunnydale landslide directly across the Yukon River both show ongoing signs of instability,” the authors write.
The research will be shared with local authorities, governments, and infrastructure planners to help mitigate risk.
Earthquake frequency in Canada
Small earthquakes are common in Canada, with the Geological Survey of Canada recording and locating an average of 4,000 earthquakes annually, or 11 per day, nationwide.
Header image: Approximate location of the Tintina fault. Cheryl Santa Maria for The Weather Network.