In existing regional geomagnetic field modeling, the smoothness of basic functions and the insufficient data constraints in marginal regions lead to the omission of detail features and extrapolation oscillations. To address these limitations and develop a high-precision marine regional geomagnetic field model, we develop a back propagation neural network (BPNN) method enhanced by particle swarm optimization (PSO). The PSO-BPNN method has the ability of adaptive learning and could extract local features. By combining the magnetic field data measured by ships with the previous model data, a high-precision geomagnetic field model of the northern South China Sea (SCS) is developed. The fitting error of the PSO-BPNN model is 18.05 nT, which is 16% and 20.1% lower than those of the traditional Legendre Polynomial (LP) and Taylor Polynomial (TP) models, respectively. The proposed PSO-BPNN model demonstrates superior robustness and higher accuracy, while retaining more magnetic signals of small geological bodies.

Moho fold structures provide critical insights into the tectonic evolution of the East China Sea. However, previous models exhibit substantial uncertainties, primarily resulting from the unaccounted gravitational effects of crustal sources and insufficient constraints on inversion parameters. In this study, we applied wavelet multi-scale analysis and the power spectrum method to remove crustal contributions, combined with an improved Bott’s method to achieve robust hyperparameter estimations. The Moho topographic model obtained through this method exhibits a significantly enhanced accuracy, with a root mean square deviation from seismic control points reduced by approximately 30% compared to other models. The resulting Moho fold structure reveals three key findings: (1) The South China Block has undergone vertical stress that forced the mantle to subduct. (2) In the northeastern and central parts of the Ryukyu Arc, vertical subduction forces are dominant. In the southwestern part of the Ryukyu Arc, vertical subduction forces are in balance with another force associated with mantle upwelling. (3) There is no interplate stress beneath the Okinawa Trough, and its crustal thinning may have been influenced by upwelling in the mantle.