Sandbox modeling on the reworking of strike-slip faulting from pre-existing thrusts: a case study of Zhangjiakou-Penglai Fault Zone in Bohai area

It is common in nature for thrust structures to form new composite structural systems under the influence of strike-slip faulting. Since the Cenozoic, the sinistral strike-slip movement of the Zhangjiakou-Penglai fault zone in Bohai basin altered the pre-existed Yanshanian thrust structure. Driven by the subduction of the Pacific Plate since the Cenozoic, the NW-trending Zhangjiakou-Penglai fault zone fault zone co-worked with the conjugate NE-trending Tancheng-Lujiang fault zone and established the modern tectonic pattern of the Bohai Bay Basin. This area is an earthquake-prone area and also an oil-gas accumulation area. To understand the mechanism of strike-slip faulting from pre-existing thrusts, we conducted sandbox modeling with various strike-slip rates and basement rigidity setting. Results show a series of thrust faults forming thrust imbricate fan and pop-up structures under compression. After the superposition of thrusting by strike-slip motion, some strike-slip faults were formed and they cut through pre-existing thrusts, presenting a flower structure. Seen in the cross-section, the larger the strike-slip rate, the more faults, the larger the fault spacing, and the more complex flower structure. In the local plastic basement model, the strike-slip zone without superposition can form a fault depression. Combined with the tectonic evolution process of the study area, the modeled results showed a similar pattern of the tectonic pattern of the Zhangjiakou-Penglai fault zone, especially those of the flower structures in the Shabei fault and Shadong fault. Therefore, the strike-slip fault played a role in controlling the tectonic trap. This study provided a reference for understanding the dynamic mechanism of tectonic superposition of strike-slip faulting and thrusting.