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First Paleoseismic Evidence of Late Quaternary Surface Rupture in the Fraser Canyon of British Columbia, Canada

The Fraser Canyon of British Columbia (BC) hosts communities and critical infrastructure including the major transportation corridor connecting Metro Vancouver to the rest of Canada. The conspicuously linear canyon follows the >400-km-long, terrane-bounding Fraser Canyon fault that separates the Coast Mountains from the Interior Plateau of BC, which has typically been considered inactive since the Oligocene. No Quaternary-active faults have been definitively identified, partially due to recent glaciation and low strain rates. From lidar images, we identified a 280 m-long, N15°W-trending, uphill-facing scarp 140 m above the canyon floor, opposite the town of Lytton, amongst several generations of glacio-fluvial terraces that post-date the Last Glacial Maximum (LGM). The scarp is adjacent to a landslide scar and is between mapped strands of the Fraser Canyon fault.
Electrical resistivity profiles across the scarp reveal sub-horizontal low-resistivity and high-resistivity zones separated by a steeply-dipping structure. The sharp contrast motivated the excavation of an 8.4-m-long, 1.7-m-deep hand-dug “Nikaia” trench that revealed three sedimentary units. From deepest to shallowest: Unit 1 is a clast-supported gravel; Unit 2 is a pebbly sand; and Unit 3 is a matrix-supported gravelly sand. Two steep, E-dipping structures show vertical separation of the Unit 1–Unit 2 contact by ~0.8 m and ≥0.5 m, respectively, and do not offset the base of Unit 3. The structures are not consistent with gravitational or glacial deformation and instead indicate surface-rupturing faulting with a reverse, east-side-up, component. We interpret Units 1 and 2 to be alluvial deposits constraining rupture to post-LGM (<17 ka), and Unit 3 to be a scarp-derived colluvial unit that caps the faults and post-dates surface rupture. Luminescence and radiocarbon dating samples were collected to refine age bounds. The observed displacement suggests at least one event of M_W ≥6.5. The Nikaia trench provides the first direct evidence for late Quaternary activity of the Fraser Canyon fault, with important implications for seismic hazard in southwestern BC.

Session: The Landscape Record of Earthquakes and Faulting - II

Type: Oral

Room: Ballroom A

Date: 4/16/2026

Presentation Time: 11:15 AM (local time)

Presenting Author: Raul Benjamin Mendoza

Student Presenter: Yes

Invited Presentation: 

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Additional Authors