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The Wyoming Craton underwent tectonic modifications during the Laramide Orogeny, which resulted in a series of basement‐cored uplifts that built the modern‐day Rockies. The easternmost surface expression of this orogeny ‐ the Black Hills in South Dakota ‐ is separated from the main trend of the Rocky Mountains by the southern half of the Powder River Basin, which we refer to as the Thunder Basin. Seismic tomography studies reveal a high‐velocity anomaly which extends to a depth of ∼300 km below the basin and may represent a lithospheric keel. We constrain seismic attenuation to investigate the hypothesis that variations in lithospheric thickness resulted in the localization of stress and therefore deformation. We utilize data from the CIELO seismic array, a linear array that extends from east of the Black Hills across the Thunder Basin and westward into the Owl Creek Mountains, the BASE FlexArray deployment centered on the Bighorn Mountains, and the EarthScope Transportable Array. We analyze seismograms from deep teleseismic events and compare waveforms in the time‐domain to characterize lateral variations in attenuation. Bayesian inversion results reveal high attenuation in the Black Hills and Bighorn Mountains and low attenuation in the Thunder and Bighorn Basins. Scattering is rejected as a confounding factor because of a strong anticorrelation between attenuation and the amplitude ofPwave codas. The results support the hypothesis that lateral variations in lithospheric strength, as evidenced by our seismic attenuation measurements, played an important role in the localization of deformation and orogenesis during the Laramide Orogeny.

 

Much of our knowledge of the North American lithosphere comes from imaging seismic velocities. Additional constraints on the subsurface can be gained by studying seismic attenuation, which has different sensitivity to physical properties. We produce a model of lateral variations in attenuation across the conterminous U.S. by analyzing data recorded by the EarthScope Transportable Array. We divide the study area into 12 overlapping tiles and differential attenuation is measured in each tile independently; and twice for four of the tiles. Measurements are combined into a smooth map using a set of linear inversions. Comparing results for adjacent tiles and for repeated tiles shows that the imaged features are robust. The final map shows generally higher attenuation west of the Rocky Mountain Front than east of it, with significant small length scale variations superimposed on that broad pattern. In general, there is a strong anticorrelation between differential attenuation and shear wave velocities at depths of 80–250 km. However, a given change in velocity may correspond to a large or small change in attenuation, depending on the area; suggesting that different physical mechanisms are operating. In the western and south‐central U.S., as well as the Appalachians, velocity variations are large compared to attenuation changes, while the opposite is true in the north‐central and southeastern U.S. Calculations with the Very Broadband Rheology calculator show that these results are consistent with the main source of heterogeneity being temperature and melt fraction in the former regions and grain size variability in the latter ones.