Moho depth of the northern Vietnam and Gulf of Tonkin from 3D inverse interpretation of gravity anomaly data

Abstract

In this paper, the authors present the result of three-dimensional (3D) direct inversion of gravity data to determine the Moho depth along the Red River Fault (RRF) zone and adjacent areas in the land territory of Vietnam and the Gulf of Tonkin. The Moho depth was calculated by 3D Parker inversion supplemented with the gravity anomaly power density spectrum. The given Moho depth and the available teleseismic and magnetotelluric Moho depth are well matched. A structural Moho map of the study region was constructed from the interpretation results. The Moho surface was uplifted along the RRF zone. The shallowest Moho depth was determined in the Red River Basin (RRB), where it ranges from 22 ± 1.0 km to 24 ± 1.0 km in the depocenter of the RRB in the Gulf of Tonkin to 27 ± 1.0 km to 29 ± 1.0 km in the Red River Delta. It is 29 ± 1.0 km to 32 ± 1.0 km from Vietri to Laocai provinces. The deepest Moho depth was found in the northwesternmost and northernmost land territory of Vietnam, where it ranges from 33 ± 1.0 km to 35.8 ± 1.0 km. A percentage of the Earth's crustal compensation is also investigated. The obtained crustal thickness and compensation state are useful for their implications regarding the geodynamics and tectonics of the RRF and surrounding region.