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Tectonic Significance and Observations of Ground Failure From the 6 December 2025 Mw 7.0 Earthquake in Yukon, Canada

Description: 

The 6 December 2025 M_w 7.0 earthquake in southwestern Yukon (60.37°N, 139.54°W) was the largest onshore earthquake in Canada in over 75 years. The earthquake highlights the complex tectonics of the St. Elias orogen and the interrelation of the Fairweather-Queen Charlotte fault system at the North American plate boundary with inboard fault systems (Totschunda and Denali faults). We study the mainshock and aftershocks through 6 January 2026, along with widespread ground failure induced by the earthquake sequence. We present double-difference relocations of the sequence, along with associated centroid moment tensor (CMT) solutions and cluster analysis, which collectively indicate a complex rupture on multiple faults along the southernmost section of the hypothesized Totschunda-Fairweather Connector fault zone. The relocated aftershocks cluster along at least two distinct fault planes: a SE-striking plane subparallel to the regional trend of the Connector fault, and a conjugate WSW-striking plane. The CMT solution for the mainshock indicates oblique fault slip and a significant non-double-couple component. Rupture complexity is further supported by CMT solutions for large aftershock events, which indicate strike-slip rupture along the primary SE-striking fault structure (Connector fault) and reverse slip on the secondary conjugate fault. Spatiotemporal evolution of aftershocks shows no pattern, until a resurgence of up to M_w 5.7 aftershocks with reverse kinematics on December 31^st that likely occurred on the secondary conjugate fault. Based on satellite imagery and a reconnaissance flight to the epicentral area, we identify over 200 landslides, extensive snow avalanches, and damage to glacial ice associated with the mainshock. Landslides are mostly restricted to the Mt. King George massif within the footprint of the aftershock sequence, whereas avalanches and damaged glacial ice are more widespread. This event has provided an invaluable opportunity to understand the tectonic structures, seismic hazard, and relations between ground shaking and mass wasting in this remote part of the Yukon.

Session: SSJ-SSOC-SSA Joint Session: Lessons from Recent Major Earthquake Sequences Around the World - I

Type: Oral

Date: 4/17/2026

Presentation Time: 02:00 PM (local time)

Presenting Author: Katherine Biegel

Student Presenter: No

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