Three-Dimensional High-Resolution Modeling of the Seismogenic Tectonics Associated with the Gaoyou-Baoying Ms 4.9 Earthquake

On July 20, 2012, the Gaoyou-Baoying Ms 4.9 earthquake occurred in a seismically weak area of eastern China, and its seismogenic structure remains controversial. Constructing a detailed three-dimensional fault model of the source region is crucial for understanding the seismogenic mechanism and assessing regional seismic hazards. This study focuses on the Gaoyou-Baoying seismic zone and, for the first time, integrates multi-source data including surface fault traces, focal mechanism solutions, precisely relocated aftershocks, shallow and deep seismic reflection profiles. Using an implicit-function modeling approach based on the Discrete Smooth Interpolation (DSI) algorithm, along with multiple rounds of iteration and sensitivity analysis, this study effectively addresses key issues such as weight allocation for multi-source data, and spatial coupling was effectively addressed, resulting in the construction of a high-precision 3D seismogenic fault model. The model reveals that the mainshock and aftershock sequences are concentrated along an S-shaped segment of a right-lateral strike-slip fault with an NNE strike, SEE dip, and dip angles ranging between 69° and 85°. The fault steepens with depth and ultimately converges at the top of the upper crustal crystalline basement, with a cutting depth of approximately 20 km. Comprehensive analysis confirms that the seismogenic structure is the Yangchacang-Sangshutou fault at the northwestern boundary of the Gaoyou Sag. This study establishes a differentiated weight constraint strategy for multi-source data and a quantitative residual control process, significantly improving model convergence and reliability. The innovative integration of implicit functions and the DSI algorithm offers strong reproducibility and generalizability, providing not only a key tectonic model for determining the seismogenic mechanism of the Gaoyou-Baoying earthquake but also a new technical approach and scientific basis for deep structural exploration and seismic hazard assessment in similar seismic zones of eastern China.