Abstract: The Huimin Depression is located in the western part of the Jiyang Depression in the Bohai Bay Basin, which has undergone a north-south extension during the Cenozoic period, forming a typical half graben structure. In the plane, a NE to near-EW oriented transtensional fault system is formed in the Central Uplift Belt (CUB) of the Huimin Sag. Vertically, the fault system of the CUB shows the characteristics from en-echelon to gradual connection from deep to shallow level. The structural characteristics of the Huimin CUB fault system have been well characterized, but its kinematic processes and controlling factors remain descriptive. In this paper, a set of transtensional analog modeling experiments are designed to investigate the faults evolution of the Huimin CUB. Our experiment reproduces the three stages of the fault system in the CUB of the Huimin Sag from early isolated segmentation, lateral propagation, and finally linking in the plane. In the profiles, the experimental results also correspond well to the structural changes of the CUB from a conjugate structure to a stepped faulting pattern along the strike. Based on the strain analysis by particle imaging velocimetry (PIV), this paper constructs a three-stage strain-distance statistics diagram for each segmented fault. It reveals the structural evolution of each segmental fault from early disconnected through lateral growth, from soft- to hard- linkage. This paper reveals the mechanism of faults development in the Huimin CUB based on sandbox analog modeling experiments. It can provide insights for the study of fault evolution and hydrocarbon forma tion in other similar transtensional basins.

Key words: Analogue modeling, transtensional structure, fault linkage, relay ramp, Huimin sag, the Central Uplift Belt