Core-refracted shear-wave anisotropy beneath the Korean Peninsula: insights into its tectonic evolution

Abstract

The tectonic history of the Korean Peninsula is marked by the Permo-Triassic collision between the North and South China blocks and the subsequently openings of the Yellow and East Seas during the Late Oligocene and Miocene. Despite well-constrained timing, the mechanisms behind these major tectonic episodes remain the subject of ongoing scientific debate. We studied seismic anisotropy from core-refracted shear-wave splitting to place constraints on lithospheric-scale and upper mantle structures and dynamics and provide insights into the tectonic evolution of the Korean Peninsula. We implemented the eigenvalue-based method to measure the splitting parameters and used the transverse energy minimization and cross-correlation techniques to validate our results. We found delay times ∼ 1.5 s which is consistent with anisotropy residing in the asthenospheric and/or lithospheric mantle. Our results strongly suggest that the anisotropy signature of past tectonic events have been preserved and that the upper asthenosphere and lithosphere have undergone coherent deformation. Based on our model, we interpret that the Hongseong-Imjingang belt is part of the collision boundary, since we observed a lateral variation of the splitting parameters coinciding with it. We suggest two possible scenarios for the continuation of the collision suture beyond this belt: (1) one offshore with the boundary coinciding with the West Marginal Fault Zone, and (2) another one onshore along the southern limit of the Gyeonggi massif. Our observations support a fan-shaped opening mechanism for the East Sea and an eastward post-collisional extension for the Yellow Sea. Lastly, the measured splitting parameters beneath the western Gyeonggi and Yeongnam Precambrian massifs appear to be in good agreement with a possible fossil anisotropy.