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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 of P wave 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. [ABSTRACT FROM AUTHOR]

The Caribbean plate subducts beneath northwest South America at a shallow angle due to a large igneous province that added up to 12 km of buoyant crust. The overriding plate lacks volcanism and exhibits Laramide‐style uplifts over 500 km from the trench. Here, we illuminate the subduction structures through finite frequency teleseismic P‐wave tomography and connect those structures to the Laramide‐style deformation on the overriding plate. We use a new data set collected from the Caribbean‐Mérida Andes seismic experiment comprised of 65 temporary broadband stations integrated with permanent stations from the Colombian and Venezuelan national networks. We identify three segments of subducting Caribbean plate with one segment completely detached from the surface. The timing of the detachment aligns with other regional events, including the uplift of the Mérida Andes, about 10 Ma. Slab buoyancy post‐detachment likely resulted in recoupling with the overriding plate, reactivation of Jurassic‐aged rift structures and subsequent uplift of the Mérida Andes. Mantle counterflow over the broken segment induced by rollback of the attached slab likely contributed to the uplift of the Mérida Andes. We conclude that the northern limit of subduction lies south of the Oca‐Ancón fault, though the fault itself may be the surface expression of the boundary. The southern limit of subduction lies south of our study area. Plain Language Summary: At the convergent boundary between the southern Caribbean and northwest South America the Caribbean plate dips, or subducts, beneath South America at angles less than 30° for up to ∼300 km inland before steepening. Such low‐angle subduction systems are unique because they produce mountains hundreds of kilometers inland. Using new data collected by the Caribbean‐Mérida Andes seismic array, which continuously recorded earthquakes for two years, we imaged the Caribbean plate to depths of 660 km and identified at least three segments, including a segment detached from the surface. The timing of the detachment ∼5–15 million years ago aligns with the uplift of the Mérida Andes of Venezuela ∼500 km inland. Both the attached and detached segments interacted with the underside of South America, compressing parts of it, and causing uplift of the Mérida Andes. The northern limit of subduction lies south of the Oca‐Ancón fault of northern Colombia and Venezuela. The southern expanse of subduction includes the Bucaramanga earthquake cluster, but the boundary lies south of our study area. By understanding how the actively subducting plate, the Caribbean, deforms the upper plate, South America, we can better assess seismic risk and understand similar systems that are no longer active. Key Points: At least three Caribbean segments subduct under South America, one detached under the Merida Andes. Detachment due to lithospheric weaknessPost‐break recoupling and rollback of slab contribute to uplift of Mérida AndesNorthern subduction boundary identified [ABSTRACT FROM AUTHOR]