Differential evolution of marginal basin fault: A case from numerical simulation of Pingbei Slope, Xihu Sag

In the East China Sea shelf basin, massive landward-dipping boundary faults were developed since the basin was born in the Mesozoic. Its structural geometry and tectonic process differ from those of other East Asian marginal basins. Previous studies focused on mainly tectonic migration of the East China Sea shelf basin, but differential evolution mechanism and its controlling factors in fault geometry were generally neglected. The northern part of the Pingbei Slope is the fault terrace zone formed by seaward-dipping normal faults, while the southern part is half-grabens controlled by landward-dipping normal faults. Differential evolution of faults in this region reflects the overall formation of the entire basin. To clarify the controlling factors, we investigated the development of landward-dipping and seaward-dipping faults by discrete element modeling. Results show that lithological differences affected the fault development. The landward-dipping normal faults tended to develop in the context of high-strength rocks, while seaward-dipping normal faults usually formed in the region of low strength. The stress orientation was another important factor for regional differential evolution, giving rise to faults development in opposite dipping. Although many slopes were developed during the formation of marginal basins, the topographic slope alone were not able to dominate the fault differential evolution. The differential evolution of the Pingbei Slope and the marginal basins might be controlled by the bedrock strength and geostress orientation. This study provided an insight and theory basis for understanding the mechanism of differential evolution in marginal basins.