Late Pleistocene-Holocene submarine active structures in the Bohai Sea

By using 5 000 km long shallow penetrated seismic data collected in recent years in the Bohai Sea, many active faults and folds were found in Late Pleistocene—Holocene unconsolidated sediments. The distribution map of active faults is plotted. Further, their distribution, shallow structures, kinematics and activities are discussed in detail. The research results show that strikes of active faults express three predominant directions: NNE, E-W and NW. The quantity of faults with an E-W-trending is the most. Fault forming is controlled by regional tectonic stress and the former faults. Most of folds are anticlines and develop along the former faults.The distribution density of active faults in the Liaodong Gulf is smaller than in other sea area. In a same structural unit, more faults developed in the boundary zone than in its inner zone. The inherited fault is usually characterized by complex fracture zone where sedimentary sequences are deformed. Fracture zones usually exhibit rake-shaped or Y-shaped on the section. The formation age of sedimentary sequences offset by faults shows that the latest tectonic movement event of most faults occurs during the middle or the end of the Late Pleistocene and parts of faults are active during the Holocene. Most of faults are dominated by the normal component, but subfaults in the Tan-Lu fault zone and the Zhangjiakou—Penglai fault zone may be with some strike-slip component besides the normal component. Activities of shallow faults in the Bohai Sea have a good correlation with the earthquake epicenter, which is valuable for seismic risk assessment.