地面回线源瞬变电磁法一维反演系统及其应用

A 1D inversion system of the ground-based loop-source transient electromagnetic method

瞬变电磁法现阶段的资料处理解释仍以一维反演为主,因此开发一套功能齐全、高效稳定的一维反演系统对进一步提高国内瞬变电磁法的应用水平仍具有重要意义。本研究开发的地面回线源瞬变电磁法一维反演系统包括了基于高斯牛顿法的最小构造反演和Occam反演,也包括了基于阻尼最小二乘法的横向约束反演和空间约束反演。以内蒙古那仁宝力格煤田玄武岩岩体形态探测为例,将该反演系统的最小构造反演和Occam反演结果与商业软件IX1D进行了对比验证,发现不同反演方法获取的电阻率二维断面图中,玄武岩岩体形态相似、电阻率范围一致;结合钻孔资料,这些一维反演结果清晰反映了玄武岩岩体除岩浆上涌通道区域外的分布形态。将横向约束反演和空间约束反演应用于该实例,结果表明:相邻测点间玄武岩岩体电阻率差异缩小,玄武岩与沉积岩界面的连续性得到增强。

The processing and interpretation of the data derived using the transient electromagnetic(TEM) method are still mainly conducted through one-dimensional(1D) inversion presently. Therefore, developing an efficient and stable 1D inversion system with complete functions is greatly significant for further promoting the applications of the ground-based loop-source TEM method in China. This study developed such an inversion system, which involves four methods, namely minimum-structure inversion, Occam’s inversion, laterally constrained inversion(LCI), and spatially constrained inversion(SCI). The first two methods are based on the Gauss-Newton method, and the others are based on the damped least-square method. This 1D inversion system was applied to detect the occurrence forms of the basalt rock masses in the Narenbaolige coalfield in Inner Mongolia. Then, the results derived from the minimum-structure inversion and Occam’s inversion used in the 1D inversion system were compared with those obtained using the commercial software IX1D. As shown in the 2D pseudosection maps of resistivity obtained by these inversion methods, the basalt rock masses have similar occurrence forms and consistent resistivity range. Compared with drilling data, these 1D inversion results clearly reflected the distribution patterns of basalt rock masses in the Narenbaolige coalfield except for the upwelling channels of magmas. Afterward, the LCI and SCI were also applied to the coalfield. The results indicate a decrease in the resistivity differences of the basalt rock masses between adjacent survey points and an increase in the continuity of the interfaces between the basalts and sedimentary rocks.