Seismic reflection imaging of a major strike-slip fault zone in a rift system; Paleogene structure and evolution of the Tan-Lu Fault system, Liaodong Bay, Bohai, offshore China

The Tan-Lu fault system in the Liaodong Bay, Bohai, offshore China, affords an exceptional opportunity to document the structural features of a major strike-slip fault using two- and three-dimensional seismic reflection data, as well as evolution of a strike-slip fault developed coeval with a rift system. The fault zone displays a relatively straight, throughgoing trace longitudinally bisecting the rift valley. It consists of positive and negative flower structures and en echelon folds in the south bay, and three parallel, flower-structure systems northward. The middle fault bifurcates northward into two semiparallel vertical fault strands. To the north, the west strand bends clockwise and merges with the east strand. The stepping pattern and orientation of en echelon structures indicate right-lateral sense and about N10-35 degrees E azimuth of slip. The fault apparently accrued about 30-40 km (20-25 mi) of post-early Eocene slip based on the current distribution of deformation zones and depocenters. Tan-Lu fault segments with clockwise and counterclockwise orientation relative to the regional slip direction are characterized by divergent and convergent structures (i.e., restraining and releasing bends), respectively. Waning of rifting eliminated the cause of a major restraining bend, putting an end to development of associated convergent structures in the south bay area. Near the central-north bay, deformation occurred along major normal faults related to the basin rifting. Although a prominent feature reflecting regional strain partitioning, the Tan-Lu fault apparently was not a major factor in the Paleogene opening of the Liaodong Bay basin and the larger North China rift basin.