Basin resonances can significantly amplify and prolong ground shaking, and accurate site‐amplification estimates are crucial for mitigating potential seismic hazards within metropolitan basins. In this work, we estimate the site amplification of long‐period (2–10 s) ground motions across northeast China for both surface waves and vertically incident shear waves. The spatial distribution of relatively large site amplifications correlates strongly with known sedimentary basins for both wave types. However, the site response of surface waves is typically twice as high as that of shear waves at most basin sites. We further show that these site‐amplification features can be well explained by predictions based on the local one‐dimensional structure at each site. Our results highlight the importance of accounting for surface‐wave contributions and demonstrate the usefulness of semi‐analytical theory for surface‐wave amplification, which may be broadly applicable in future seismic hazard analysis.