CONTINUOUS FULL STRESS TENSOR MAPPING IN THE CONTERMINOUS U.S. AND ALASKA: APPLICATION TO FAULT SLIP POTENTIAL MODELS

More than 2 billion years of tectonism have crisscrossed North America with faults of nearly every orientation. Modern intraplate earthquakes typically exploit these inherited faults, yet variations in the crustal stress field control which orientations are locally prone to reactivation. This study first presents updated stress maps of the continental U.S. and Alaska using inversions of focal mechanisms formally constrained by in-situ data (e.g., from boreholes) where available. The lower 48 dataset has enlarged ~50% relative to previous works, California excluded, which sharpens resolution in many areas although most features have been previously documented. The Alaska update is the first in 15 years and first since the Earthscope Transportable Array. Key, novel findings include an along-strike transition from oblique extension in the south to contraction at the north end of the Queen Charlotte-Fairweather Fault (with implications for tsunamigenesis), ponderous complexity and localized crustal extension above the tear in the subducting Pacific/Yakutat slab, and a vast region of NNE–SSW to NE–SW extension across western Alaska from the Bering block past the western Brooks Range that suggests escape tectonics. Next, full stress tensors are calculated using 3D crustal density models derived from seismic velocity, gravity, and topography to constrain the vertical stress magnitude. Finally, force balance implies that the stress field is continuous, allowing seamless estimation of the full stress tensor at seismogenic depths across the continent. In Alaska, the fault slip potential is computed for all 1700 segments included in the USGS National Seismic Hazard Model, highlighting the most likely nucleation points for cascading multi-segment ruptures, quantifying susceptibility to hydrologic triggering, and other uses. In the intraplate eastern U.S., fault slip potential modeling near suspected Quaternary features identifies likely causal faults and winnows paleoseismic targets. For example, few previously mapped faults near Charleston, SC are compatible with the modern stress field, yet both the Gants/Summerville and Ashley Bluffs faults recently posited by Hough and Bilham are near optimal orientations. Future uses of the continuous full stress tensor models include detailed dynamic rupture simulations and proactive management of induced seismicity.