Finley, T., Gosselin, J.M., Biegel, K.M., Lipovsky, P.S., Cronmiller, D.C., Schaeffer, A.J. and Dettmer, J., 2026. The December 6, 2025 Mw 7.0 earthquake in Yukon, Canada: Tectonic significance and observations of ground failure. In: Yukon Exploration and Geology 2025, A. Stuart, L.H. Weston and S.K. Schultz (eds.), Yukon Geological Survey, Government of Yukon, p. 131–148.. Abstract: The December 6, 2025 moment magnitude (Mw) 7.0 earthquake in southwestern Yukon was the largest onshore earthquake in Canada in over 75 years. It caused no casualties or damage to the built environment but offers insight into the complex active tectonics of the St. Elias orogen and hazards posed by major faults in the Yukon. It also caused widespread landslides and avalanche activity, providing an opportunity to study relationships between ground shaking and mass wasting. Here, we use double-difference relocation to refine the location of the mainshock and 3280 ensuing aftershocks. Based on satellite imagery and a reconnaissance flight to the epicentral area, we compile a preliminary inventory of over 200 landslides and other surface effects caused by the event. During the December 12, 2025 flight, no evidence of a surface rupture was observed. The areal extent of landslide occurrences was also considerably smaller than expected based on empirical data from past earthquakes, possibly due to the cold temperatures and presence of permafrost. The earthquake relocations and landslide distribution indicate that the main rupture and strongest shaking occurred beneath the Mt. King George massif. We infer that the rupture occurred on the southernmost section of the hypothesized Totschunda-Fairweather Connector fault. Slip initiated with strike-slip motion, rupturing northwestward, and may have activated a conjugate reverse fault toward the northwest segment of the rupture.

We provide the first conclusive evidence of numerous large (>Mw 7.5) surface-rupturing earthquakes in the Quaternary on the Tintina fault Offsets to Early and Middle Pleistocene glaciofluvial ter...