A stress province boundary and tractions on the North American plate

Abstract

Stress provinces, characterized by nearly constant directions and relative magnitudes of horizontal principal stresses, are potentially informative of the forces acting on a lithosphere plate. This applies most strongly to stress provinces which occupy a large part of a plate, such as the Mid-Continent Stress Province of North America identified by Zoback and Zoback¹. We have used fractures known as breakouts in oil-wells, which are controlled by the in situ stress, to show that this stress province extends through the western Canadian sedimentary basin to the arctic coast. There is a strong possibility that a uniform stress orientation, with greatest compression NE–SW, is co-extensive with the North American continent east of the Rocky Mountains excluding the Appalachian and Gulf of Mexico stress provinces. We further report new breakout orientations in the far northwest of Canada, which locate the boundary between the Mid-Continent Stress Province and an Alaskan stress province, with largest compression NNW–SSE, probably controlled by the subduction of the Pacific plate under Alaska.