基于可控源电磁法阻抗信息的有限内存拟牛顿法三维反演

本文研究了利用阻抗信息进行可控源电磁勘探有限内存拟牛顿法三维反演的技术。首先用理论模型来验证有限内存拟牛顿法反演的准确性和可行性。观测参数为复阻抗Z_xy分量，采用交错网格有限差分方法计算模型响应，反演采用有限内存拟牛顿法。数值模拟结果表明：有限内存拟牛顿法反演迭代速度较快，每4 min迭代一次，拟合差由146.00下降到1.78，收敛稳定；异常体的位置与理论模型吻合较好，有效地验证了有限内存拟牛顿法可控源三维反演的正确性。为了进一步验证该方法的实用性，将其应用到隐伏钼矿可控源电磁勘探工作中。工区的反演结果显示：在工区北西段深部存在高阻异常，其上为低阻异常。截取过钻孔的3号测线发现，-500~-100 m的位置表现为低阻，东侧存在向上涌起的高阻。推测此低阻为矿化蚀变带，延伸较深。该异常与钻探资料揭示的钼矿脉一致，证明了反演结果的准确性。因此，利用可控源观测得到的阻抗信息进行有限内存拟牛顿法三维反演，可以获得可靠的三维电阻率分布。

Three-Dimensional Inversion Based on the Impedance Information of Controlled Source Electromagnetic Method by Limited Memory Quasi-Newton Method

In this paper, a three-dimensional limited memory quasi-Newton algorithm inversion for controlled source electromagnetic method based on impedance information is discussed. Firstly, the synthetic data from theoretical model is used to verify the accuracy and feasibility of the limited memory quasi-Newton inversion method. The observed data type is Z_xy, using staggered grid finite difference method to calculate the forward responses, and the limited memory quasi-Newton algorithm to perform the inversion. The numerical simulations show that the limited memory quasi-Newton inversion method has fast iteration speed, 4 minutes in one iteration, and the fitting error decreases from 146.00 to 1.78 with stable convergence; the location of the anomalous body agrees well with the theoretical model, which validates the limited memory quasi-Newton method for three-dimensional inversion of controllable sources electromagnetic method. To further verify the practicability of this method, it is applied to the exploration of concealed molybdenum deposits. The inversion results show that there are high resistivity anomalies in the deep part of the northwest and low resistivity anomalies in the upper part of the survey area. The profile of line 3 through the borehole shows a high conductivity region at the depth of -500 m——100 m, and a high resistant anomaly in its east. It is speculated that the low resistivity zone is a mineralized alteration zone with deep extension. The anomaly is consistent with the molybdenum vein revealed by drilling data, which proves the accuracy of the inversion. Therefore, the reliable three-dimensional resistivity distribution can be obtained by inverting the impedance information with limited memory quasi-Newton three-dimensional inversion method.