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Topic

Neotectonics of major faults in the Canadian Cordillera

School of Earth and Ocean Sciences

Date & location

• Wednesday, April 23, 2025
• 9:30 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Edwin Nissen, School of Earth and Ocean Sciences, University of Victoria (Co-Supervisor)
• Dr. John Cassidy, School of Earth and Ocean Sciences, UVic (Co-Supervisor)
• Dr. Kristin Morell, School of Earth and Ocean Sciences, UVic (Member)
• Dr. Andrew Schaeffer, School of Earth and Ocean Sciences, UVic (Member)
• Dr. Christopher Bone, Department of Geography, UVic (Outside Member)

External Examiner

• Dr. Magali Rizza, Département des sciences de la Terre et de l'atmosphère, Université du Québec à Montréal

Chair of Oral Examination

• Dr. Peter Dietsch, Department of Philosophy, UVic

Abstract

The Canadian Cordillera is an 800 to 1000 km-wide accretionary orogen comprised of numerous terranes and crustal fragments, which are bounded and crosscut by major, mature fault zones. Despite being most active during Mesozoic to early Cenozoic mountain building, the Cordillera continues to be tectonically active in the present, with elevated seismicity and strain rates compared to the stable continental interior. The role of the major faults within the Cordillera in accommodating ongoing deformation has remained unclear, in part due to sparse seismic and geodetic instrumentation, but also due to the challenging surficial environment (i.e., recent glaciation, high precipitation, dense vegetation) that has hindered tectono-geomorphic and paleoseismic studies.

In this thesis, I leverage a recent expansion of high-resolution topographic data coverage across the Canadian Cordillera to investigate the geomorphic signature of faulting in the landscape. I make use of new airborne lidar (light detection and ranging) data made available by provincial and territorial governments, and I also collect new lidar using a novel drone system – the first of its kind applied to tectonic geomorphology. In addition, I take advantage of the new ArcticDEM dataset, derived from optical satellite imagery, and covering all regions north of the 60^th parallel. These datasets enable the mapping of subtle fault scarps, as well as the glacial landforms that constrain the timing of past ruptures.

I focus on three major fault zones: the Tintina fault in northern Yukon, the Eastern Denali fault in southwestern Yukon, and the Southern Rocky Mountain Trench fault in southeastern British Columbia. The Tintina fault is a major, ~1000-km-long fault that has accommodated over 400 km of dextral offset in the Eocene but is generally not considered active today. I show that it has in fact ruptured numerous times throughout the Quaternary, is capable of future large earthquakes (>M_w 7.5), and may be late in a seismic cycle, representing a major seismic hazard to the region. The Southern Rocky Mountain Trench fault is thought to have been a locus of significant extensional deformation in the Eocene. Using new airborne lidar, surficial mapping, and shallow geophysical surveys, I provide evidence of multiple extensional surface ruptures in the Holocene. A potential decrease in slip rate through time is speculated to be related to glacial isostatic adjustment. The Eastern Denali fault, a major terrane-bounding fault, is already known to be a potential seismogenic source, however its kinematics and the level of tectonic activity have remained topics of debate. Using a new, comprehensive lidar dataset covering nearly the entire fault, I demonstrate that its kinematics are dominantly dextral despite being in an overall compressive setting, highlighting the role of inherited fault geometry.

The results of this work have significant implications for seismic hazard assessments in Canada. Much of Canada’s National Seismic Hazard Model is based on historical and instrumental records of seismicity to define probabilities of shaking over broad areas. My work will enable the inclusion of discrete fault sources in the hazard model. In addition to seismic hazard, these geomorphic studies shed light on the driving mechanisms and characteristics of neotectonic deformation across the Cordillera and provide broader insight into how pre-existing, mature faults behave in regions of moderate to low strain.