‘Sleeping Giant’ Fault Under Canada Shows Major Earthquake Potential

After 12 millennia of relative inactivity, a geologic fault that stretches across the territory of Yukon, Canada, and Alaska now appears capable of producing a major earthquake, according to a new study. The findings point to an underrecognized source of seismic hazard in northwestern Canada.

Scientists previously believed that the Tintina fault, which extends roughly 620 miles (1,000 kilometers) from northeast British Columbia through the Yukon and Alaska, remained quiet for the last 40 million years. These new findings, published July 15 in the journal Geophysical Research Letters, challenge that theory. Using high-resolution topographic data, a team of researchers identified an 81-mile-long (130-kilometer-long) segment of the Tintina that produced multiple large earthquakes far more recently. The last one occurred about 12,000 years ago, and stress has been building on the fault ever since. When it ultimately ruptures, the quake could be powerful—potentially exceeding magnitude 7.5.

Such a quake would threaten small Yukon communities situated near the Tintina, particularly Dawson City, home to over 1,500 people. Severe shaking could trigger landslides and damage near highways and mining infrastructure. Over the last 20 years, there have been a few small earthquakes of magnitude 3 to 4 along the Tintina, but no large ruptures, according to Finley. He and his colleagues set out to determine whether this fault is capable of producing larger quakes.

“In the last couple of years, there’s been a much more widespread availability of high-resolution topographic data,” Finley told Gizmodo. His team used data collected from satellites, airplanes, and drones to scan the area near the Tintina for fault scarps. These features form when earthquakes rupture Earth’s surface, serving as evidence of past quakes.

The researchers found an 81-mile-long (130-kilometer-long) series of fault scarps passing within 12 miles (20 kilometers) of Dawson City. To determine the timing of the earthquakes that created them, they observed landforms left by glacial incursions that occurred 12,000, 132,000, and 2.6 million years ago. This revealed that the fault has produced multiple large earthquakes over the last 2.6 million years, likely slipping several meters each time.

However, the 12,000-year-old landforms were not offset by the fault, indicating that there hasn’t been a major rupture since then. Over these millennia, the Tintina has been accumulating strain at a rate of about 0.2 to 0.8 millimeters per year, according to the study. Based on this, Finley and his colleagues estimate that roughly 20 feet (6 meters) of total slip deficit have built up.

Eventually, the building strain will cause the fault to rupture and potentially produce a major earthquake, Finley said. However, that does not mean this region is in immediate danger. “Although large earthquakes can occur on this fault, they likely occur with many thousands of years between them,” Finley said. “It’s impossible to say, from our current understanding, whether one is imminent or thousands of years away.”

Still, the possibility of a major Tintina quake warrants some reconsideration of the seismic hazard in Northwestern Canada. The nation’s National Seismic Hazard Model (NSHM)—which informs seismic building codes and other engineering safety standards—does not currently recognize the Tintina as a discrete seismogenic fault source, according to a UVic release. Finley’s findings will eventually be integrated into the NSHM and shared with local governments and emergency managers to improve earthquake preparedness. “What our information does is refine the location of where some of the largest hazards would be in this seismic hazard model,” he said.