Abstract:

The North China Basin, with great thick sedimentary layers, is located in the eastern part of the North China Craton and is one of the important sedimentary basins in eastern China. There are a large number of buried faults in the North China Basin. Some of buried faults are strong activity and have experienced major earthquakes, such as the 1679 Sanhe-Pinggu M8 earthquake and the 1976 Tangshan M_S7.8 earthquake. The geometric distribution and depth of these buried faults remain uncertain. Thus, it is very important to study spatial distribution and the intersecting relationships of the main faults in the region, and high-resolution aeromagnetic data is key.
In the paper, the high-precision aeromagnetic field data of the North China Basin are collected and are reduced to the pole at variable latitudes. Using the vertical first-order derivative and tilt-derivative edge-enhancement methods, and with reference to existing geological data, the geometric distribution and intersection relationships of the major faults are reinterpreted and corrected. The derivative methods have inherent limitations in the sedimentary area; the correction results are compared with previous data to ensure the reliability of the interpretation results. Moreover, the Euler deconvolution method is used to estimate the apparent depth of some buried faults in the basin. Its cutting depth is inferred and verified with other geophysical results.
The result shows that the aeromagnetic field is divided into four blocks: the chaotic magnetic zone of the northern Yanshan uplift, the high magnetic zone of the western Taihang uplift, the medium-high magnetic zone of the central North China Basin, and the low magnetic zone of the southern Luxi uplift. The North China Basin is characterized by multiple secondary structural units with alternating NE-trending uplifts and depressions. The 59 major faults are interpreted and corrected using the aeromagnetic field and its derivative, with faults mainly oriented NNE and NE, supplemented by NW, NS, and near-EW orientations. In the NNE direction, among them buried faults such as the Baoding-Shijiazhuang Fault, the Cangxi Fault, the Cangdong Fault, and the Tangshan Fault exhibit beaded bands, linear anomalies, magnetic gradient strip and so on. In the NW direction, the magnetic field characteristics of the Xiadian Fault, the Baodi Fault, and the Nankou-Sunhe Fault are faint, showing magnetic conversion and fault-bent strips, suggesting they played a regulatory role in structural deformation.
The Euler results show the apparent depth and cutting scales of 13 buried faults within the basin. Among them, 6 buried faults are middle-shallow scale faults: the Huangzhuang-Gaoliying Fault, the Nankou-Sunhe Fault, the Baodi Fault, the Cangdong Fault, the Cangxi Fault and the Liaocheng-Lankao Fault; and 7 buried faults are middle-deep scale faults: The Baoding-Shijiazhuang Fault, the Shunyi-Liangxiang Fault, the Xiadian Fault, the Jiyunhe Fault, the Tangshan Fault, the Chengxi-Yangerzhuang Fault and the Handan Fault. Multi-scale aeromagnetic computation and inversion provide a new technical approach for investigating the spatial distribution of buried faults. For large areas, especially sedimentary basins with great thick sedimentary layers, this technology is used for preliminary exploration of the geometric distribution and depth of buried faults.

Key words: North China Basin, aeromagnetic field, buried fault, planar geometric distribution, Euler deconvolution, apparent fault depth

摘要：

针对巨厚沉积层的华北盆地, 文中利用较高精度的航磁场数据开展隐伏断裂的空间展布研究。在参考前人地质资料基础上, 通过航磁场变纬度化极处理, 采用垂向一阶导数与斜导数边界增强方法, 解释修正了区域主要断裂的平面几何分布与交切关系。鉴于导数方法在沉积覆盖区的局限性, 将修正结果与前人资料进行对比分析, 以确保解译结果的可靠性。同时, 采用欧拉反褶积方法反演主要隐伏断裂的断层视深度, 推断其下切规模及延展深度, 并与前人结果进行对比验证。结果表明: 基于航磁场及其导数场解释修正了59条主要断裂, 断裂以NNE和NE向为主, 以NW、 SN、 近EW向为辅, 其中NNE向的保定-石家庄断裂、 沧西断裂、 沧东断裂、 唐山断裂等隐伏断裂表现为串珠状条带、 线性异常、 磁性梯度带等, 而NW向的夏垫断裂、 宝坻断裂、 南口-孙河断裂等磁场特征较弱, 表现为磁性转化、 折弯条带, 推测在构造变形中起到了调节作用。通过欧拉结果得到了盆地内13条隐伏断裂的断层视深度, 其中7条断裂为中深层断裂, 包括唐山断裂、 邯郸断裂、 夏垫断裂等; 6条为中浅层断裂, 包括宝坻断裂、 沧东断裂、 沧西断裂等。航磁场多尺度反演工作可为隐伏断裂空间展布研究提供新的技术手段。

关键词: 华北盆地, 航磁异常, 隐伏断裂, 平面几何展布, 欧拉反褶积, 断层视深度