Seismic Imaging Reveals Ongoing Modification of Craton Margins in Northeast Asia

Abstract Cratonic margins are commonly modified, yet the processes responsible remain debated. The Korean Peninsula, situated between adjacent cratons, the Japan Trench, and a back‐arc system, provides a natural setting to investigate this problem. Using 4 years of dense seismic observations, we image upper‐mantle structure beneath the peninsula with P‐wave tomography that incorporates a prescribed anisotropy model to reduce velocity artifacts. The results reveal a pronounced east–west contrast, with slow velocities beneath the eastern peninsula and fast velocities beneath the western peninsula. The eastern low‐velocity anomalies are consistent with hot and/or compositionally modified mantle, whereas the fast western anomalies may indicate ongoing lithospheric modification beneath the peninsula.