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Crustal Stress in Alaska and NW Canada: New Insights Into Intraplate Deformation and Fault Slip Potential

Description: 

The crustal stress field represents the summed effects of plate-boundary and basal tractions, gravitational body forces, and surface loads. In turn, local stress controls the seismogenic potential and coseismic slip behavior of crustal faults. Here, we leverage the quadrupling of focal mechanisms from intraplate Alaska and NW Canada over the past 15 years to produce an inversion-based crustal stress model that constrains the causes and kinematics of deformation. Edge tractions alone produce smoothly varying intraplate stress fields marked by horizontal stresses that decay with distance inland, and this characterizes first-order stress patterns: Maximum horizontal compression (σ_H) is broadly margin-perpendicular (e.g., N40E in British Columbia, N25W in the eastern Brooks Range, N80W in the Bering block) and reverse-oblique faulting near the plate boundary grades to strike-slip ~500 km inland. Deviations from these trends must result from other processes. In the arcuate Mackenzie Mountains σ_His range-perpendicular, rotating from N65E to N5E along the range while regional σ_Htrends N30E. Collision of the translating crust with the craton edge or a divergent mantle flow at the keel could create this stress perturbation. Western Alaska (from the Iditarod-Nixon Fork Fault across the Bering Sea) is extending southward. Dynamic return flow northwest of the Pacific slab may increase gravitational potential energy, causing the switch in deformation style, while minor far-field compression guides margin-parallel stretching. In this heterogeneous stress field, the seismogenic potential of intraplate faults cannot be assessed with a single model. We build stress models for 1803 segments on 84 crustal faults from the USGS National Seismic Hazard Model to quantify fault slip potential, predict coseismic behavior (e.g., rake), and identify along-strike stress variations that could influence rupture segmentation. This modeling underscores the importance stress heterogeneity in fault kinematics and ultimately seismic hazard.

Session: Compiling Active Faults for Improved Hazard Modeling from Cascadia to Alaska - I

Type: Oral

Date: 4/17/2025

Presentation Time: 04:30 PM (local time)

Presenting Author: Will

Student Presenter: No

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