This is a flagship paper that presents our work investigating updates to the way we characterize seismic site response in sedimentary basins of varying size, as well as non-basin areas. The paper details our efforts which resulted in changes to the mean estimates and associated variability as it relates to ground motion hazards, going beyond the ergodic 1D representations. The findings from this work are published in Earthquake Spectra, and will impact the National Seismic Hazard Model products that are used in engineering designs. See the publications page of this website to get more information and access.