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The Zhangjiakou‐Penglai Fault Zone (ZPFZ) is an NW‐trending strike‐slip fault zone in Eastern China that contains abundant petroleum resources and has induced massive seismic hazards. It is left‐lateral and behaves as a conjugate relationship with the Tan‐Lu Fault Zone (TLFZ). Present studies on the ZPFZ are mainly conducted on its seismology and field exposure features, with subsurface characteristics and evolution history poorly understood. In this study, we investigated the ZPFZ in the western offshore Bohai Bay Basin based on the detailed interpretation of 3D seismic data, specializing in subsurface geometric characters and evolution history. The profile flower structure and plan broom‐like pattern featured the ZPFZ in the study area and indicate its sinistral strike‐slipping. We further investigated and discusssd the Cenozoic evolution history based on evidence in (a) distinguished tectonics in fault releasing and restraining bends, (b) strata thickness map before and after the strike‐slipping, and (c) geometry of composite flower structures. The result suggests the evolution of the ZPFZ mainly comprises three stages: (a) the initial extension from 65 to 38 Ma, (b) the sinistral strike‐slipping in transtension from 38 to 25 Ma, and (3) the sinistral strike‐slipping in transpression from 25 Ma to present. The proposed evolution of the ZPFZ had good consistency with that of the conjugate TLFZ and was closely related to the Cenozoic surrounding plate tectonism, especially the Pacific Plate subduction. [ABSTRACT FROM AUTHOR]

The western offshore Bohai Bay Basin (BBB) is located at the intersection of the Zhangjiakou–Penglai Fault Zone (ZPFZ) and the Huanghua–Dongming Fault Zone (HDFZ). Exploration experience proves that faults' activity played an import role in hydrocarbon accumulation, whereas characters and evolution of the fault system remain poorly understood. In this study, characters and evolution of the fault system were investigated through abundant seismic data from oil fields. Six NE and two NW strike‐slip faults were identified by composite flower structures on seismic profiles and show broom‐like or en echelon patterns with different scales in plan view. Massive flower‐like structures were observed, which serve as an indicator of early extension and consequent shear activity. Based on published physical modelling, the different plan forms and scales of strike‐slip faults were deciphered as an outcome of diverse strike‐slip displacements. The character and evolution of the fault system were investigated using fault activity rate, balanced restoration, and typical‐structure analysis. The result suggests that the NW‐trending faults have a more intense fault activity and strike‐slip faults in the north, and the east have larger displacements than those in the south and the west. Considered together with the basin evolution, we suggested a three‐stage fault evolution model for the fault system in the study area, mainly comprising (a) early extension; (b) mid transtension, and (c) late transpression, which resulted from multiple geodynamic events during the Cenozoic. Our study reveals that the ZPFZ and the HDFZ have a significant impact over faults in the western offshore BBB, which is demonstrated by unusual intense fault activity in the extension period and different strike‐slip displacement in the strike‐slip period. [ABSTRACT FROM AUTHOR]