Three-dimensional S-wave azimuthal anisotropy and its tectonic implications in the central and eastern North China Craton

The subduction and rollback of the Western Pacific Plate and the expansion of the Tibetan Plateau have significantly influenced the tectonic evolution of the North China Craton (NCC). However, the detailed characteristics of the associated deep dynamic processes remain poorly understood. Seismic anisotropy serves as a key indicator for probing deformation and dynamics in the Earth’s interior. Based on surface wave data recorded by dense seismic arrays, this study applied Eikonal tomography method to obtain Rayleigh wave azimuthal anisotropy images at periods of 12–120 s across the central and eastern NCC. We further inverted these data for a 3-D shear-wave velocity structure and azimuthal anisotropy down to 260 km depth. Our results reveal a prominent low-velocity anomaly in the upper mantle beneath the central-eastern part of the study region, where the fast direction is generally E–W. We propose that this low-velocity anomaly likely originates from the dehydration of the stagnant Western Pacific slab in the upper mantle, which induces partial melting that subsequently ascends to the base of the lithosphere. Meanwhile, the east–west anisotropic pattern is likely associated with eastward flow of the asthenosphere caused by the retreating subduction of the Pacific plate. To the east of the Ordos Block, an N–S trending low-velocity anomaly below 180 km depth exhibits weak anisotropy, which may be attributed to deep material upwelling associated with eastward asthenospheric flow and abrupt lateral variations in lithospheric thickness. In the northeastern part of the Craton, the fast direction in the asthenosphere and below shifts to NW–SE, distinct from that beneath the North China Plain. This difference may reflect variations in the subduction angle and rollback rate between the Japan Trench and the Ryukyu Trench. Our findings provide new observational constraints on lithospheric deformation and deep dynamic processes in this region.