Novel regional–residual anomaly separation technique for evaluating Moho configuration and crustal density structure beneath the East Vietnam Sea (South China Sea)

• Novel gravity anomaly separation technique was developed, tested and applied. • Crustal density ranges from 2.54 to 2.90 g/cm 3 across East Vietnam Sea. • Estimates of Moho depth varies from 8–32 km, deepest near the Red River Basin. • Moho depth values align with previous OBS Moho depth estimates in the study area. • The study offers geodynamic, tectonic, and mineral exploration insights. This study presents a novel gravity anomaly separation technique and demonstrates its application in delineating the crustal density structure and Moho depth configuration of the East Vietnam Sea (South China Sea). The proposed method employs correlation analysis between Bouguer gravity anomalies approximated by higher-order two-variable polynomial functions and their upward-continued counterparts at varying altitudes to isolate the regional gravity field. The resulting regional component, associated with long-wavelength gravity signals, was used to model the depth to the Moho boundary, while the residual component, reflecting short-wavelength anomalies, was inverted to estimate lateral variations in crustal density. The results reveal that crustal density varies from approximately 2.54 g/cm 3 in sedimentary basins to about 2.90 g/cm 3 along the mid-oceanic ridge, indicating significant lithological contrasts. The Moho depth ranges from ∼8 km beneath the mid-oceanic ridge to ∼32 km beneath the southwestern margin, particularly near the Red River basin. These observations correlated well with previous interpretations derived from ocean bottom seismometer data, validating the effectiveness of the approach. This study develops an integrated regional–residual separation and inversion framework that refines constraints on crustal architecture while offering critical geodynamic insights for delineating tectonic domains with potential resource significance. It offers a new perspective for gravity-based crustal modeling and provides a first-order geophysical framework for understanding the lithospheric structure of the East Vietnam Sea. The method also demonstrates potential for global and broader applications in tectonic studies and regional geodynamic investigations.