In Canada’s Yukon, the Tintina Fault has the potential for an earthquake exceeding magnitude 7.5. Dawson City lies dangerously close to the epicentre and could be severely affected by the shaking.
A research team led by the University of Victoria has identified a previously little-noticed geological fault in Canada’s Yukon Territory as a significant earthquake hazard. It is the approximately 1,000-kilometre-long Tintina Fault, along which the researchers mapped a 130-kilometre-long series of fault scarps and pressure ridges. Their analysis shows that in the geologically recent past (the last 2.6 million years), the fault has produced multiple large, surface-rupturing earthquakes — contrary to earlier assumptions that it had been inactive for 40 million years.
“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,” Dr. Theron Finley, a geoscientist at the University of Victoria and lead author of the study, said in a press release.
The traces of the historic earthquakes only became visible through high-resolution topographic data from satellite imagery as well as lidar surveys conducted by aircraft and drone. “The expanding availability of high-resolution data prompted us to re-examine the fault, looking for evidence of prehistoric earthquakes in the landscape,” explains Finley.
The models reveal linear terrain offsets that would otherwise remain easily hidden in the boreal forest. The fault zone runs less than 20 kilometres from Dawson City — close enough that a future major earthquake could cause considerable damage there.
In particular, the lateral displacements of dated glacial landforms provided the team with crucial clues. Moraines and gravel terraces from a glaciation during the transition from the Pliocene to the early Pleistocene, around 2.6 million years ago, are offset by more than a kilometre, while younger features from the last interglacial period are displaced by several dozen metres. Early Holocene terraces (around 12,000 years old), on the other hand, show no offset — an indication that no major earthquake has ruptured the surface since that time.
A long period of quiet — yet for the authors, this does not mean the fault doesn’t pose any risk. On slowly moving, long-established faults, very long intervals can occur between major earthquakes. “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,” says Finley. Such an event could reach a magnitude of at least 7.5.
The existing seismic monitoring network has provided little indication of any hazard, as historical records and modern seismic data cover only a few centuries. According to the study, geodetic measurements are also often too imprecise to detect movement rates in the sub-millimetre range. Parts of the northwestern Yukon remained largely ice-free during the last glaciation — one reason why ancient fault features there are exceptionally well preserved.
Tectonically, the Tintina Fault is among the major structures of the Northwest: since the Eocene, it has accumulated hundreds of kilometres of lateral displacement, as shown by the study published on 15 July in Geophysical Research Letters. Even though its current slip rate is low — 0.2 to 0.8 millimetres per year — such long-established faults are still capable of producing very large events, especially as the fault in the Yukon runs remarkably straight over long stretches.
The consequences of a major earthquake would be severe. In Dawson City (population around 1,600), strong to very strong shaking would be expected. Key transport routes and mining facilities could be damaged. Landslides are an additional threat: the Moosehide slide north of the town and the newly discovered Sunnydale slide on the opposite bank of the Yukon River are already considered unstable.
The official hazard maps will also need to be updated. Canada’s National Seismic Hazard Model does account for large earthquakes in central Yukon, but so far it has not listed the Tintina Fault as a distinct source. The new findings are to be incorporated into future revisions — with implications for building codes, engineering standards, and emergency plans. The results will also be shared with local authorities and emergency services to improve earthquake preparedness.