Origin of Three-Dimensional Crustal Stress Over the Conterminous United States

The crustal stress field determines continental deformation, including intraplate seismicity and topographic undulations. However, the sources of observed crustal stress patterns remain debated, with proposed mechanisms including lateral variations in gravitational potential energy and mantle flow, the latter of which comprises plate boundary interactions and basal tractions. Here, we present a series of geodynamic models that simultaneously consider lithospheric and mantle dynamics in the same physical framework, based on which we investigate the sources of crustal stress over the conterminous U.S. The data-oriented nature of these models allows us to systematically explore the relative contributions of different dynamic sources to the three-dimensional crustal stress field. These models reveal that forces from the plate boundaries play a dominant role in generating the directional pattern of long-wavelength horizontal crustal stress across the conterminous U.S. In the central U.S., especially regions of high-topography, lithospheric density heterogeneities locally modify the crustal stress field. Similarly, mantle flow beneath the North American plate modulates crustal stress orientation in the eastern U.S., particularly in regions with thin lithosphere. Furthermore, we find that a denser-than-ambient lithospheric mantle beneath the central and eastern U.S. is required to match the observed continental-scale E-W topographic contrast.