Under Pressure: The Lateral Stress Transferring and Localization Among Lithospheric Blocks as Revealed by Seismology and Machine Learning

Abstract

The Rocky Mountains feature intermittent landforms, with mountains separated by relatively undeformed basins. Previous studies have suggested a connection between pre- Laramide crustal weaknesses and the localization of deformation. Although seismic tomography results reveal significant heterogeneity in the lithospheric mantle, the connection between deformation and deeper lithospheric structure has received comparatively little attention. In southern China and Iberia, thicker lithospheric blocks appear to be associated with undeformed regions. We investigate the possible connection between deformation, topography, and lithospheric structure, in Wyoming and surrounding regions. Newly available data from local arrays, including the recent CIELO and FlexArray BASE experiment, enable us to pursue a better characterization of the lithosphere than was previously available. We employ seismic attenuation inversion, seismic velocity tomography, and seismic event detection to reveal the contrast of lithopshere’s thickness and strength among different blocks. We find a moderate correlation between seismic velocity above 150 km, path-integrated seismic attenuation, conductivity, and topography in the Laramide uplifts of Wyoming and South Dakota Multiple small-scale anomalies in both velocity and attenuation spatially coincide with the basement-cored uplifts. In addition, seismic events as detected by state-of-the-art machine learning detectors suggest the relative abundance of earthquake events in regions that are associated with higher attenuation and slower velocity around the depth of the Lithosphere-Asthenosphere Boundary. The results imply the presence of colder and thicker lithosphere beneath the basins and warmer and thinner lithosphere beneath the mountain ranges. Given the modest amount of shortening across any individual range, we assume the lithospheric structure is not a consequence of contraction and existed Pre- Laramide. Therefore, localization of deformation is likely associated with pre-existing variations in lithosphere strength, which may have contributed to the formation of crustal weaknesses along which the uplift of ranges like the Bighorn Mountains and the Black Hills occurred.