A fault line is a fracture or space of weakness in the Earth’s crust where tectonic plates meet, and are the main source of earthquakes. The Tintina fault stretches around 1,000 kilometres (621 miles) northwest across the region through to Alaska. It runs parallel to the Yukon River and is one of the great fault systems in western North America. Over its lifetime, it has shifted sidewards by 450 kilometers (280 miles) but was thought to be inactive for at least 40 million years.
However, new topographic imaging from satellites, aircrafts and drones have led researchers to discover a 130 kilometre (80 miles) portion of the fault near Dawson City that shows signs of several large earthquakes during the Quaternary Period (spanning the last 2.6 million years to the present). This finding suggests the fault may still be active and could produce significant future earthquakes.
Dr Theron Finley, lead author of the recent article in Geophysical Research Letters, said: ‘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. The expanding availability of high-resolution data prompted us to re-examine the fault, looking for evidence of prehistoric earthquakes in the landscape’
Seismic hazard estimates across Canada are usually informed by historical earthquakes records including Indigenous oral histories, archived documents, and readings from modern seismic networks but these only go back a few hundreds of years. But major faults can lie dormant for thousands of years between large earthquakes, which means that seismic risks may go undetected without geological investigation. So the team, which consisted of researchers from UVic, the Geological Survey of Canada, and University of Alberta, used high-resolution topographic data from the ArcticDEM dataset from satellite images, as well as from light detection and ranging (lidar) surveys from airplanes and drones. They found a series of fault scarps (a small step-like offset that forms due to a vertical shift along a fault line) passing within 20km of Dawson City.
They also found that glacial landforms, which are around 2.6 million years in age, are laterally offset across the fault scarp by 1000m. Others, which are 132,000 years old, are laterally offset by 75m. These findings confirm the fault has slipped in multiple earthquakes throughout the Quaternary period, at several metres in each event. The researchers also found that landforms, around 12,000 years old, are not offset by the fault, suggesting no large ruptures have happened since. The fault continues to strain at an average rate of 0.2 to 0.8 millimeters per year, so poses a future earthquake threat. A magnitude of 7.5 or greater would cause severe shaking across the city, and could pose a threat to nearby highways and mining infrastructure. The region is also prone to landslides, which could be seismically triggered. Dr Finley said: ‘We determined that future earthquakes on the Tintina fault could exceed magnitude 7.5. 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’
Tintina fault
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