Inherited Fault Angle Control on Basin Inversion Structures in the East China Sea: Insights From Numerical Simulations

Basin inversion involves the contractional reactivation of inherited extensional structures, and inherited fault dip is known to influence reactivation potential: during inversion, lower‐angle inherited faults are generally more favorably oriented for reverse reactivation than steep normal faults. In the Xihu Sag of the East China Sea, the Jiaxing and Ningbo segments of the Central Anticline Structural Zone show contrasting inversion styles. The principal inherited faults beneath these segments differ in dip, we combine seismic‐stratigraphic interpretation with two‐dimensional discrete‐element models to test whether inherited fault dip explains this difference. The experiments include one reference model and inherited faults dipping 30°, 45°, 60°, and 80°, each subjected to extension followed by equal‐magnitude shortening. The models reproduce three inversion modes: the 30° and 45° faults undergo efficient reverse reactivation and accommodate most shortening by slip reversal along the inherited plane; the 60° fault produces a hybrid fault‐fold system in which shortening is partitioned among partial reactivation, fold amplification, and breakthrough thrusting; and the 80° fault is only weakly reactivated as shortening is transferred into fold growth and a footwall shortcut thrust. The Jiaxing segment contains steeper inherited faults associated with tighter and higher‐relief folds, whereas the Ningbo segment contains more moderately dipping faults associated with broader, lower‐amplitude folds and more continuous inherited‐fault reactivation. Together with the seismic observations, these results suggest that dip‐dependent shortening partitioning explains the contrasting inversion styles of the Jiaxing and Ningbo segments and provides a framework for interpreting structural differences in inverted rift basins.