Enhanced Gravity-Geologic Method by Considering Nonlinear Effects of Surrounding Seafloor Topography: A Case of Bathymetric Prediction in the Sea of Japan

Summary The gravity-geologic method (GGM) is an approach that utilizes marine gravity anomalies and shipborne bathymetric data to invert seafloor topography by resolving short-wavelength gravity anomalies through the Bouguer plate approximation. Such an approximation ignores the nonlinear effects caused by surrounding seafloor topographical undulations that actually exist in short-wavelength gravity anomalies, and thus leaving the space for further modification of GGM. This study thoroughly derives the relationship between seafloor topography and gravity anomaly (GA), as well as the formula of GGM. Then, we propose a self-adaptive method to improve the accuracy of the inversion significantly: the enhanced gravity-geologic method (EGGM). The method employs the equivalent mass line method to approximate the nonlinear gravitational effects of the surrounding seafloor topography to correct the short-wavelength gravity anomalies. By introducing two optimal density contrast parameters, EGGM has been designed to effectively integrate the combined effects of various nonlinear factors to a certain extent. The accuracy of the seafloor topography models, produced with a spatial resolution of 1'×1', was evaluated over the study area (132 °E-136 °E, 36 °N-40 °N) located in the Sea of Japan. The results indicate that the accuracy of EGGM has a relative improvement of 13.73% compared to that of GGM in the overall study area, while the accuracy of both models is higher than that of the SIO_unadjusted model. The study further investigated the feasibility and stability of EGGM by examining the accuracy of both GGM and EGGM in various water depth ranges and areas with diverse terrain characteristics.