An Inversion Method for Moho Depth Distribution Characteristics in the Bohai Sea and Its Adjacent Areas Based on the Improved Bott-Parker Method

Abstract. The Bohai Sea and its adjacent areas (116.5°~123.5°E, 36.5°~41.5°N) are located in eastern China, serving as a critical marine-continental transition zone in the eastern part of the country. Acquiring high-precision distribution characteristics of the Moho depth in this region is of great significance for understanding the local deep tectonic features and the distribution of mineral resources such as oil and gas. Owing to the high cost of seismic surveys, it is difficult to obtain the overall Moho topography of the region. Therefore, based on the latest generation of SWOT-03 satellite gravity data, this study uses the improved Bott-Parker method to invert a high-resolution Moho topography with a resolution of 1′×1′ in the Bohai Sea and its adjacent areas. First, Bouguer correction was applied to the SWOT-03 free-air gravity anomalies to derive the Bouguer gravity anomalies of the study area. To separate the Moho gravity anomalies, which reflect the distribution characteristics of the Moho depth, from the Bouguer gravity anomalies, an 8th-order wavelet multiscale decomposition was performed on the Bouguer gravity anomalies, generating the corresponding wavelet approximations and wavelet details. Then, the average radial logarithmic power spectrum analysis method was used to calculate the approximate source depths of the wavelet details of each order, thus obtaining the gravity anomalies that represent Moho undulation. Finally, the improved Bott-Parker method was employed to invert the high-resolution Moho topography of the Bohai Sea and its adjacent areas. Specifically, the improved Bott-Parker method obtains the initial Moho topography via linear regression using known seismic Moho data and Moho gravity anomalies derived from wavelet multiscale decomposition, and then continuously corrects the Moho topography using the gravity difference between the forward-calculated values from the Parker method and the observed gravity values. Compared with the traditional Parker-Oldenburg method, the improved Bott-Parker method avoids the need to set the cutoff frequency of the filter. The results demonstrate that the average Moho depth in the Bohai Sea and its adjacent areas is 32.98 km, with a variation range of 24.26~57.22 km, and multiple Moho uplift and depression zones are present in the region. The inverted Moho topography is basically consistent with the Crust1.0 global crustal model, which can well reflect the distribution characteristics of the Moho depth in the Bohai Sea and its adjacent areas as a whole. This study has certain guiding significance for understanding the regional tectonic features and conducting oil and gas exploration.

Keywords: SWOT-03 satellite gravity data; Moho depth; Gravity inversion; Wavelet multi-scale decomposition；Improved Bott-Parker method