3D Moho Architecture Along the Sumatra Oblique Subduction Margin: Insights from GOCE Cross-Gravity Gradients

Abstract

Sumatra Island is an active subduction margin controlled by the subduction of the Indo-Australian Plate beneath Sundaland, oblique deformation, and the activity of the Great Sumatran Fault; thus, it is an important region for examining regional crustal structure. This study aims to determine the three-dimensional Moho topography beneath Sumatra using the cross-gravity gradient components from the GOCE satellite, namely Γxy, Γxz, and Γyz. The approach used was the Vening Meinesz–Moritz isostatic inversion with Tikhonov regularization, while the regularization parameter was selected using the L-curve method. Each component was inverted separately to produce the Mxy, Mxz, and Myz models, then combined into a multi-component model Mxyz. The results showed that all cross-gradient components displayed a regional northwest–southeast pattern aligned with the physiographic orientation and tectonic framework of Sumatra. The Moho models from the inversion showed similar regional geometry, but the combined Mxyz model provided the most stable solution with a depth range of 27.1–46.9 km. Spatially, the Moho was relatively shallower in the oceanic forearc domain to the southwest and became deeper beneath the main landmass of Sumatra, especially in North Sumatra, West Sumatra, South Sumatra, Bengkulu, and Lampung. Compared with the reference model, all GOCE-based models tended to produce a deeper Moho, but Mxyz showed the smallest residual distribution with a standard deviation of 7.05 km and an RMS of 11.85 km. Spectral analysis also showed that Mxyz best preserved the regional signal while suppressing extreme local fluctuations. These results confirm that GOCE cross-gravity gradients are effective for reconstructing the regional Moho topography and revealing crustal segmentation beneath Sumatra.