Boundary Identification and Extraction of Fault Structure in the South China Sea Using Full Tensor Gravity Gradient Combination

  Objectives  The South China Sea is located at the junction of three major plates, i.e, Eurasian, Indo-Australian, and Pacific Plates. Affected by the superposition of the Tethys tectonic domain in the west and the Pacific tectonic domain in the east, it has a special tectonic background and a unique tectonic location. The complex geological structure of the South China Sea and the interactions between different plates have made the tectonic problems in the South China Sea still controversial, including the location of the ancient South China Sea suture zone and the division of geological tectonic units. The study of fault structure is important for gravity interpretation and is closely related to the division of tectonic units.

  Methods  The full tensor gravity gradient data contains a large amount of information and higher frequency signal components and can better describe small anomaly characteristics, and thus it is widely used in geophysics. On the basis of the full tensor gravity gradient combination, this paper studies the fault identification and extraction method in the South China Sea.

  Results  Multiple gravity gradient boundary rec‍ognition methods are compared to clarify the advantages and disadvantages of each method, including the direct use of the three-component gravity gradient method and the full tensor gradient combination meth‍od. Through comparative analysis, the traditional three-component gravity gradient method cannot effectively balance the amplitude of deep and shallow anomalies. When both positive and negative anomalies appear spontane‍ously, false boundary results may be generated. The full tensor gravity gradient combination method can not only effectively avoid the defects of traditional methods but also obtain boundaries with good continuity and convergence. In addition, the boundary identified by the T _cos value and the T _tan value of the full tensor gravity gradient component combination is consistent with accurate positioning and the better convergence, and the accuracy of the horizontal position of the fracture structure or the boundary of the geological body is improved. Moreover, this paper also uses the improved Canny boundary extraction method to accurately obtain the plane position of the South China Sea fault. The obtained South China Sea fault boundary is consistent with the T _cos and T _tan values, and the boundary of the South China Sea structural unit is accurately given.

  Conclusions  The characteristics of the margins of the South China Sea Basin are different, with the west, east, south, and north as a strike-slip fault, a trench subduction fault, a compression fault, and a tensile fault, respectively. The South China Sea fault strikes are mainly in NE and NW directions, followed by NEE, NW, EW, and near SN directions.