Study of the structural characteristics of the Earth’s crust in Cao Bang province and adjacent areas using gravity data

Cao Bang province and adjacent areas in northern Vietnam are affected by modern tectonic fault zones, leading to frequent landslides and earthquakes. Understanding the deep structural characteristics of the Earth’s crust is crucial for advancing the study of geodynamics and geological hazards. Most previous studies on the deep structural characteristics of this region used only a few analysis methods, and their results were not highly reliable. Aiming to provide highly reliable information about the deep structural characteristics of this region, this study we apply a calculation process with a combination of gravity data analysis techniques and earthquake data. Specifically, the depth results obtained from the 2D modeling problem are utilized as inputs to construct an initial 3D model, thereby improving the accuracy of the depth of the crystalline basement and Moho surfaces. By integrating the results from these techniques with earthquake data, a more accurate fault system map can be developed. Maximum horizontal gradient, tilt angle, constrained two-dimensional inversion, Euler deconvolution, 2D modeling and 3D inversion are the main techniques used. The results of the study area show that the fault system is quite complex. Large faults can be easily recognized such as F1 (Pho Day River), F2 (Yen Minh – Phu Luong), F3 (Sub-meridian fault) and F4 (Cao Bang – Tien Yen). The depth of the crystalline basement surface varies from 0 to 4.32 km, with the basement outcropping in Bac Kan province and reaching deep depths in the Cao Bang and That Khe basins. The depth of the Moho surface varies from 28.77 to 38.01 km. The shallowest depth of the Moho surface is located in the northern area of Cao Bang province, the southern area of Bac Kan province, the southeastern area of Lang Son province, and the Cao Bang and That Khe basins. The deepest depth value of the Moho surface is located in Bac Kan province, where the crystalline basement is outcrop. The study results have shown the effectiveness and high reliability of applying calculation processes and combining analytical methods.