剩磁影响下的南海三维磁性结构反演策略

The Strategy of 3D Inversion of Magnetic Structure from South China Sea Affected by Strong Remanent Magnetization

磁力数据是研究南海海域深部结构、地质构造及构造演化的重要资料,南海海域三维磁性结构反演研究,将有助于为丰富和深化如上地质问题的认识提供定量的地球物理证据。然而由于南海地处低磁纬度区且南北跨度大,同时存在强剩磁影响,这些复杂因素的交织为南海磁测数据处理与反演提出巨大的挑战。为应对如上挑战,提出利用等效源技术与磁异常模量反演相结合的策略,开展南海海域三维磁性反演。考虑到低磁纬度、南北向磁倾角的剧烈变化以及地球曲率对频率域异常模量计算的影响,借助等效源技术可实现异常模量在空间域的稳定计算,继而基于模量数据进行三维模量反演,在剩磁影响和总磁化方向难以判定的情况下,可直接反演出地下的三维磁性分布。理论模型试验和南海东北部海区磁异常三维模量反演试算结果表明,等效源技术与磁异常模量反演相结合的策略是复杂条件下三维磁性反演的有效途径。

The magnetic data is an important data for studying deep crustal structures, regional geological structure, and tectonic evolution in South China Sea (SCS). The research of 3D magnetic structure inversion would help to provide the geophysical quantitative evidence for enriching and deepening the understanding of the above geological issues in SCS. However, the processing and inversion of magnetic data in SCS are faced with significant challenges due to intertwined influence factors, such as low magnetic latitudes, a large scale from south to north and the influence of strong remanent magnetization. To tackle these challenges, we present a comprehensive research strategy through the joint use of the equivalent source technique and amplitude inversion to construct 3D subsurface magnetism distribution from observed magnetic data. Firstly, in order to overcome the prohibitive difficulties in the wave-number domain due the low magnetic latitudes, dramatic changes of the magnetic inclination along longitude direction and the curvature of the earth, we use equivalent source technique to calculate the amplitude stably in the space domain. We then carry out amplitude inversion to generate 3D subsurface distribution of magnetization strength in the case that strong remanent magnetization is present and the general magnetization direction cannot be estimated. The test results of both synthetic model and field data in northern SCS demonstrate that the combined equivalent source technique and amplitude inversion is a feasible and effective approach to construct 3D magnetic structures under the complicated conditions in SCS.