A New Genetic and Evolutionary Model for the Ningbo Structure in the Xihu Sag, East China Sea Shelf Basin: Insights from Seismic Interpretation and Analogue Modeling

The central inversion tectonic belt of the Xihu Sag is a typical inversion structural zone in the East China Sea Shelf Basin and a key target for hydrocarbon exploration. The Ningbo structure underwent five evolutionary stages—rifting, post-rift transition, depression, transpressional inversion, and regional subsidence—during which the stress regime evolved from extension to transpression-dominated strike-slip deformation. This study employs seismic interpretation, fault-throw analysis and sandbox analogue modeling to clarify its genetic mechanism and controlling factors. The results show that the fault system exhibits characteristics typical of strike-slip deformation, including high-angle master faults and well-developed flower structures. Along strike, fault throw alternates between normal and reverse displacement over short distances, forming a “dolphin effect,” reflecting spatial alternation between transtensional and transpressional domains. Comparison of three experimental models demonstrates that the overlap and lateral spacing of pre-existing basement faults primarily control deformation style. Greater overlap and closer spacing promote through-going fault linkage and the formation of a principal displacement zone, generating a narrow, continuous uplift belt. A three-dimensional genetic model is established, providing a unified explanation of structural patterns, with implications for similar inversion systems.