三维张量CSAMT响应特征研究

张量CSAMT(可控源音频大地电磁法)能完整地描述三维的地电信息，更适应复杂地质条件下的地质勘探。采用将总场分解为一次场和二次场的策略，用差分近似微分形成大型线性方程组，通过解方程组得到张量CSAMT三维正演结果。通过计算低阻和高阻目标体的响应，发现卡尼亚视电阻率和视阻抗相位对低阻体表现为低值异常，对高阻体表现为高值异常，视阻抗相位达到极值时的频率比视电阻率达到极值时的频率要高。张量CSAMT对低阻体比高阻体更灵敏，在同样条件下，高阻体的异常区位置相比于低阻体会上移。某工区的勘察案例表明，根据卡尼亚视电阻率异常能定性地判断地下异常体的存在，为解决地质类问题提供了依据。本研究为张量CSAMT三维反演提供了基础。

Response Characteristics of 3D Tensor CSAMT

Tensor CSAMT can fully describe three-dimensional (3D) geoelectric information, and is more suitable for geological exploration under complex geological conditions. Strategy of decomposing the total field into primary and secondary field is adopted here, and the large-scale linear equations are formed by different approximate differentiation. The 3D forward modeling results of tensor CSAMT are obtained according to these equations. By calculating the response of low-resistivity and high-resistivity targets, the Kania apparent resistivity and apparent impedance phase show low and high anomaly for low-resistivity and high-resistivity body, respectively. The frequency of which the apparent impedance phase reaches the extreme value is higher than that when the apparent resistivity reaches the extreme value. Tensor CSAMT is more sensitive to low-resistivity body than to high-resistivity body. Under the same condition, the abnormal area position of high-resistivity body moves upward compared with low-resistivity body. A survey case in the study area shows that the underground abnormal body can be qualitatively judged via the Kania apparent resistivity anomaly, which facilitates geological problem solving. This study provides a basis for tensor CSAMT 3D inversion.