What do you call a 1,000-kilometer-long fault line that has slept for 40 million years, suddenly and quietly starting to wake up right under your feet? Geoscientists have a new name for Canada’s Yukon Territory’s Tintina fault: a seismic hazard hiding in plain sight uncovered by the persistent gaze of modern LiDAR and topography mapping.
For many years, the Tintina fault had been thought of as a geologic relic, a structure that had finished its tectonic job in the Eocene. Nonetheless, as Theron Finley, author of a new paper, pointed out, “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.” That assumption has now been turned on its head with the charting of fault scarps stretching 130 kilometers near Dawson City, charted using high-resolution topography and LiDAR data that were collected from satellites, airplanes, and drones.
The technical advancement is in using airborne and drone-borne LiDAR to break through the dense boreal forest cover to reveal the bare-earth surface. The technology that transmits laser pulses and measures their returns permits the generation of digital elevation models (DEMs) with sub-meter accuracy. Such precision is necessary in the Yukon, where a few-meter-high and wide fault scarps may persist for millennia but are beyond naked-eye observation or standard aerial photography. As Finley described it, “The expanding availability of high-resolution data prompted us to re-examine the fault, looking for evidence of prehistoric earthquakes in the landscape.”
The data are persuasive. Glacial landform offsets at 2.6 million years are approximately 1,000 meters on each side of the fault, while the younger 132,000-year-old features are offset 75 meters. These offsets, cross-validated with glacial chronology, indicate multiple large-magnitude earthquakes throughout the Quaternary period. On the other hand, landforms produced 12,000 years ago are displacementless, indicating more than quiescent interval exceeding 12 millennia since the last major rupture.
Despite this, the fault is not quiescent. The fault continues to build tectonic stress at a rate of between 0.2 to 0.8 millimeters per year. Over 12,000 years, this amounts to a slip deficit of some six meters a magnitude 7.5 or greater earthquake if released in one episode. “We determined that future earthquakes on the Tintina fault could exceed magnitude 7.5,” Finley said. “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.”
The implications are much more than merely intellectual interest. The rupture would generate violent shaking in Dawson City, threaten vital mining infrastructure, and in an already weakened region, potentially trigger landslides. The Moosehide and Sunnydale landslides, lying in close proximity to the fault, are also showing signs of active instability and could be seismically induced by a subsequent earthquake further endangering the surrounding populations and infrastructure.
From a seismic hazard assessment perspective, the findings are groundbreaking. The Tintina fault has never been treated as a discrete seismogenic source within Canada’s National Seismic Hazard Model (NSHM). Future revision of the NSHM will include new evidence drawn from LiDAR-aided mapping and geomorphic analysis, influencing seismic building codes and engineering practice in the Yukon and elsewhere to protect lives and infrastructure.
The Tintina case highlights the strength of LiDAR as a geological hazard mapping tool. Its capacity to penetrate vegetation and produce high-resolution terrain models has made fault detection a new science, allowing subtle geomorphic expressions indicative of ancient and recent tectonic activity to be pinpointed. As the technology itself matures with more and more miniaturized sensors, cloud computing, and AI-powered data analysis, its use in seismic hazard evaluation and disaster preparedness will only expand making it a gold standard for earth scientists and engineers.
For earth scientists and advanced geology enthusiasts, reactivation of the Tintina fault is a sobering reminder: even the oldest of tectonic giants may wake up, and only the sharpest eyes of technology can find them.
