Moho structure in Sulawesi area based on spherical gravity inversion

The geophysical inversion based on spherical coordinate system is widely used in regional scale research, which can take the Earth's curvature into account. This paper presents the method of calculating Moho depth variations based on spherical gravity inversion. The inversion objective function is established by considering data error and the smoothness regularization. In addition, the method is applied to study the Moho depth variations in Sulawesi area. Sulawesi area is located in the convergence zone of the Pacific Plate, Philippine Sea Plate, Eurasian Plate and Indo-Australia Plate with young subduction zones and complex fault systems which make it an ideal place to study the initiation mechanism of subduction and many other cutting-edge scientific issues. At present, there are not many geophysical observations in the study area, so we lack reliable seismological data to constrain the Moho depth. There are few overall knowledges of the Moho structure in the study area. In this study, we extract the gravity anomaly that reflects the Moho structure from the Bouguer gravity field by matched filtering. And the reference Moho depth in the study area is given by spectrum analysis. In the inversion, three hyperparameters including the regularization parameter, the Moho density-contrast, and the reference Moho depth are estimated using the method of hold-out cross-validation twice. At last, Moho depth is obtained by iterative inversion. According to our result, the average Moho depth in Sulawesi area is about 20. 0 km. The Moho depth ranges from 9. 2 km to 33. 3 km, which is shallower in the sea area, about 10. 0 similar to 20. 0 km, while deeper in the land area, about 25. 0 similar to 33. 0 km. Our result is in general consistent with that in Crust1. 0 model, previous gravity inversion research and seismological data, so it can be seen as a reasonable result in Sulawesi area.