应用全张量重力梯度组合识别并提取中国南海断裂

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

断裂构造研究是重力解释的一项重要工作,与构造单元划分密切相关。全张量重力梯度数据以其信息量大、含有更高频的信号成分,能更好地描述小的异常特征等优点在地球物理领域中得到广泛应用。基于全张量重力梯度组合研究中国南海断裂识别及提取方法。首先,比较多种重力梯度边界识别方法,包括直接利用重力梯度三分量法和全张量梯度组合法,分析它们的优缺点。通过对比分析,传统重力梯度三分量方法不能有效地均衡深浅异常的振幅,当异常中同时出现正负异常可能产生假的边界结果。全张量重力梯度组合法不仅可以有效地避免传统方法的缺陷,而且获得的边界还具有良好的连续性和收敛性。其次,利用改进的边缘检测计算理论边界提取法确定断裂的精确平面位置,得到了与全张量梯度组合法一致的结果。由此推断,南海断裂以北东走向和北西走向为主,北东东、北西、东西和近南北走向为辅。

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 Tcosvalue and the Ttanvalue 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 Tcosand Ttanvalues,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.