The Moho Depth of the South China Sea Basin From Three‐dimensional Gravity Inversion With Constraint Points and Its Characteristics

Abstract

We calculate the gravity anomalies due to lateral changes in bathymetry from an independent topography compilation, and those due to changes in sediment thickness and density. To obtain the Moho depth and the crustal thickness of the South China Sea basin, the 3‐D gravity inversion method is employed, based on an “initial model of fluctuating interface” constrained by the control points from seismic data and sonobuoys. And then, the gravity data is corrected for the lithospheric thermal gravity anomaly within continental margin due to lithosphere thinning. Over most of the South China Sea basin, the Moho depth ranges between 8∼14 km, the crustal thickness is 3∼9 km. The NNE trending fossil spreading center of the East and the Southwest Basin extend to 112°E, the Moho depth is more than 12 km, the crustal thickness is above 6 km in the spreading center. However, the crust of the spreading center at the northwest basin is not obviously thickened. In the northern margin of the southwest basin, south of Zhongsha block, there is a crustal thinning belt, nearly EW trending, where the crustal thickness is about 9∼10 km. The 14 km isoline of the Moho depth and the 9 km isoline of the crustal thickness are very close to the Continent‐Ocean Boundary.

Estimating the Lithospheric Flexure of a Plate with Non-uniform Flexural Rigidity: A Quantitative Modelling Approach

“…The key to calculating lithospheric flexure via the FD method is to obtain accurate spatial distributions of the Moho and T e . The Moho depth is usually recovered via gravity inversion (Wu et al 2017). There are currently two main methods for mapping the spatial variations in T e based on the coherence between the Bouguer gravity anomaly and topography/bathymetry.…”

“…Joint inversions that involve gravity measurements and other geophysical constraints are generally employed to reduce the non-uniqueness of the best-fit models (Chappell & Kusznir 2008;Bai et al 2014;Ji et al 2018). Here we perform a three-dimensional gravity inversion that is constrained by seismic observations (Wu et al 2017) to recover an accurate Moho topography. the Moho and initial interface can then be obtained by substituting this difference into the gravity inversion equation (Oldenburg 1974…”

“…We largely follow the procedure outlined in Wu et al (2017), except for the implementation of Eq. (1) to determine the interface difference during each iteration of the inversion, to ensure that both the Moho depth and Bouguer gravity anomaly (Bg) satisfy the 123 inversion equation (Oldenburg 1974) after the Moho topography is recovered.…”

“…This is still an 77 idealised model that considers the vertical density variation in the lithosphere. Furthermore, we 78 obtain T e variations via the fan wavelet coherence method (Kirby & Swain 2004 and the 79 Moho topography via a constrained gravity inversion method (Wu et al 2017). We then employ 80 the finite-difference (FD) method to model lithospheric flexure.…”

Estimating the lithospheric flexure of a plate with non-uniform flexural rigidity: a quantitative modelling approach

“…Numerous studies have used T e to analyse lithospheric rheology and deformation (Pérez-Gussinyé et al 2009;Chen et al 2015;Ji et al 2017Ji et al , 2020Lu et al 2020). However, this idealised term does not refer to an existing thickness or physical layer within the Earth, but instead corresponds to the thickness of an ideal elastic plate that undergoes the same deformation as the lithosphere under the same loads (Watts 2001). As T e is a periphrastical parameter for understanding lithospheric rheology and deformation, directly modelling lithospheric flexure should provide key insights into the nature of tectonic evolution and dynamics.…”