Is it possible for a fault line, silent for millennia, to suddenly awaken with catastrophic force? That is the question now ringing out among Canada’s earthquake scientists, in the wake of a shocking find on Yukon’s Tintina Fault. For decades, the Tintina nearly 1,000 kilometers long and having shifted 450 kilometers sideways over its geologic life was assumed to be quiescent, its last great activity dating more than 40 million years ago. But with the advent of a new generation of high-resolution topographic imagery, that supposition has been turned on its head, uncovering a seismic risk of far greater reach than the Yukon backcountry.
The game-changer was the use of sophisticated remote sensing technologies. Researchers from University of Victoria, Geological Survey of Canada, and University of Alberta used satellite-based ArcticDEM, airborne, and drone-based LiDAR surveys to penetrate thick boreal forest cover and reveal subtle fault scarps imperceptible to conventional mapping. As Theron Finley, the senior author of the recent research, put 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 outcome: a 130-kilometer section in the vicinity of Dawson City, mapped by a string of scarps passing within 20 kilometers of the town, each a mute witness to ancient seismic disturbances that lasted for thousands of years.
The technical innovation is the combination of multi-platform data. ArcticDEM, which was sourced from stereo satellite imagery, offered extensive regional coverage, whereas airborne and drone LiDAR produced sub-meter resolution digital elevation models that could exclude vegetation and emphasize ground-level discontinuities. This level of detail is critical: fault scarps in forested areas are usually only a few meters high and wide but can stretch tens or hundreds of kilometers. As shown from Korean and Slovenian research, LiDAR’s capability to “see through” the canopy has transformed active fault detection in difficult conditions where classical fieldwork is practically unfeasible.
The paleoseismic record derived from these data is impressive. Glacial features dated at 2.6 million years are displaced by 1,000 meters, while structures 132,000 years old exhibit 75 meters of lateral displacement. Most strikingly, landforms less than 12,000 years old are unbroken, suggesting that there have been no surface-rupturing earthquakes since the close of the last glaciation. The fault, however, is still accumulating strain at 0.2 to 0.8 millimeters annually, which over 12,000 years amounts to a slip deficit of six meters sufficient to release a magnitude 7.5 or higher earthquake were it released in one episode. “We determined that future earthquakes on the Tintina fault could exceed magnitude 7.5,” Finley warned. “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 engineering and hazard consequences are significant. The large-scale rupture would produce intense ground shaking at Dawson City, pose risks to essential mining and transportation facilities, and potentially activate landslides in an area already unstable. The Moosehide and Sunnydale landslides, both in near proximity, are closely monitored for movement signs and could be activated by intense seismic waves with a large-scale event.
To seismic hazard practitioners, the Tintina find underscores the limitations of a dependence on past earthquake catalogs particularly in intraplate environments where seismic cycles may run for millennia. Seismic hazard models in Canada have historically been constructed from a mosaic of oral tradition among Indigenous populations, archive records, and contemporary seismic networks, seldom projecting more than a few centuries in time. The record of the Tintina Fault shows that large faults can be silent for thousands of years in between large ruptures, hiding their real hazard potential until exposed by geological exploration.
The application of these discoveries into Canada’s National Seismic Hazard Model (NSHM) has just begun. Although the NSHM currently factors in the risk of large earthquakes in central Yukon, the Tintina Fault was never before considered an individual seismogenic source. Its inclusion of slip rate, segmentation, and paleoseismic history will have a direct impact on seismic building code, infrastructure planning, and emergency preparedness for all communities in the region.
This episode highlights a larger trend in earthquake science: the integration of remote sensing, geochronology, and engineering modeling is now critical to realistic seismic risk assessment in far-flung and forested areas. As demonstrated by similar investigations in East Asia and the Alps, the interplay between LiDAR, InSAR, and field trenching has the potential to revolutionize our knowledge of fault behavior, slip rates, and the likelihood of multi-segment ruptures critical parameters for next-generation hazard models that need to predict the unexpected.
