All Aligned on the Western Front of North America? Analyzing the Stress Field in the Northern Cordillera

Abstract

This study presents the first rigorous statistical analysis of the present-day crustal stress along the western margin of the North American Plate, covering the entire Canadian Cordillera and Alaska. Using circular statistics and geometric tests, we develop a regional stress province model that constrains the directions of first-order stresses. Observed stresses from the World Stress Map database and other published sources are compared with modeled directions derived from plate boundary stresses, mantle drag, and gravitation-induced body forces. Our results show that plate boundary forces dominate the stress field, particularly those associated with the convergent and transform boundaries between the Pacific/Yakutat and North American plates. Local stress modifications are caused by slip partitioning related to oblique plate boundary geometries. Active regions at the northeastern edge of the Cordillera coincide with the superposition of stresses from both the Pacific–North American transform boundary and the Arctic/North Atlantic ridge push. Despite their large distance from active plate boundaries, the alignment of stress trajectories in the Richardson Mountains and Mackenzie Mountains results in stress amplification and eventually deformation. Conversely, misalignment and hence stress reduction explains the seismic quiescence in the Canadian Rocky Mountains. Thereby, the lithospheric-scale structural inheritance along the Tintina Fault and the northern Rocky Mountain Trench acts a major deflector of far-field stresses. Second-order drivers, notably gravitation-induced body forces, further modify stress fields, particularly along the northern slope of the Brooks Range and within the North American foreland of the Cascadia subduction zone.