Role of inherited fault reactivation in accommodating multistage deformation in the southwestern margin of the Ulleung Basin, East Sea (Sea of Japan): Insights from 3D seismic interpretation

The southwestern margin of the Ulleung Basin, the East Sea (Sea of Japan), preserves complex structural and stratigraphic architectures produced by a multistage tectonic evolution in response to the Cenozoic convergence of the Indian and Pacific/Philippine Sea Plates to the Eurasian Plate. However, the origin, geometry, kinematics, and interrelationship of geological structures that evolved through the multistage tectonic deformation remain elusive, particularly regarding the role of structural inheritance in the evolution of the basin. Based on comprehensive 2D and 3D multichannel seismic reflection and well data, we present structural interpretations of regional-scale faults, folds, and growth strata in the southwestern margin of the Ulleung Basin, with a focus on inherited fault reactivation. In addition, a revisited deformation framework is proposed, involving back-arc extension/normal faulting (stage 1: ca. 23 to 15 Ma), positive inversion/reverse faulting (stage 2: 15 to 10.6 Ma), and strike-slip faulting/local transpression (stage 3: 10.6 Ma to present). Here, we illustrate how the reverse reactivation and propagation of segmented NE–SW normal faults and subsequent strike-slip movement have led to the complex structural and stratigraphic architectures presently evident in the study area. Notably, the final overprinting of a strike-slip deformation on the inherited NE–SW faults during deformation stage 3 has caused significantly damaged stepovers and tips, in which secondary faults and folds might control hydrocarbon migration/trapping and leakage. In this context, we suggest that the gentle antiformal Gorae Ⅰ structure is linked in origin to the Gorae Ⅴ structure, bearing a commercially viable gas trap as a detachment fold system formed by local transpression during deformation stage 3. Our comprehensive 3D structural seismic interpretation increases the understanding of Cenozoic multistage deformation, highlighting the impact of different tectonic drivers affecting the eastern marginal sea of the Eurasian Plate.