Structural evolution characteristics and analogue modelling of the arcuate fault zone in the western slope of Xihu Sag, East China Sea shelf basin

The Xihu Sag has experienced multi-stage tectonic movements, creating favorable conditions for hydrocarbon accumulation and making it a highly prospective exploration target. The arcuate fault zone on the western slope is characterized by complex fault interactions, yet the contrasting development of its northern and southern segments remains controversial. Based on 3D seismic interpretation, we identify NNE-trending extensional faults in the north and NNW-trending strike-slip faults in the south, along with graben, Y-shaped, and negative flower structures. Balanced cross-section analysis reveals alternating extensional and compressional regimes across different evolutionary stages. Sandbox physical modeling experiments suggest that the arcuate fault zone experienced a four-stage evolution: independent growth in the rifting period, linkage of fault-depression transformation, segmented growth in the depression period and termination of development in the inversion period. Since the Cenozoic, NW-SE-oriented regional extension promoted normal fault systems in the north, whereas reactivation of the NW-trending Gushan basement fault in the south induced strike-slip deformation. The final hard linkage between the two segments formed the arcuate fault zone. Comparison between experimental models and geological observations highlights the pivotal role of the plastic layer, which, together with basement fault reactivation, jointly controlled the development of the arcuate fault zone.