Investigating the gravity variable-density inversion method in complex geological settings: application to the South China Sea

Abstract Gravity data constitute a crucial dataset for probing the deep crustal structure and tectonic evolution of the South China Sea (SCS). Gravity inversion can effectively estimate the depth of Moho interface and crustal thickness. However, the inversion of the Moho interface in the SCS faces significant challenges, primarily due to the complex geological configurations where diverse crustal types coexist. In such settings, the density contrast between the crust and mantle exhibits three-dimensional (3D) variations, characterized by a vertical gradient and horizontal abrupt changes. To address these challenges, we introduce a strategy that employs an enhanced variable-density model, which is composed of multiple polynomials to delineate the complex varying crustal compositions, in conjunction with seismic data as constraints for the inversion of Moho depths. The efficacy of this approach is demonstrated through a synthetic example and its application to the Moho interface inversion in the SCS. The inverted Moho depth, derived crustal thickness, and stretching factor provide valuable insights into the interpretation of major tectonics in the SCS.