巷道影响下三维全空间瞬变电磁法响应特征

使用磁偶极源模拟三维均匀介质内部低阻体的全空间响应特征,采用非均匀网格和时间步长推导了瞬变电磁场的三维时域有限差分格式,并根据多个测点计算的数据,绘制了磁场和磁场对时间导数的等值线图,分析了瞬变电磁场的传播规律,以及巷道和交界面对场的影响特征。结果表明:在磁场穿过低阻体与大地的交界面时,磁场的扩散速度降低,衰减变慢;随着迭代次数的增加,磁场以低阻体为中心形成等值线环。巷道在早期对场影响较大,晚期则不明显,为解释全空间TEM异常提供参考。

Response Characteristics of the 3D Whole-Space TEM Disturbed by Roadway

The 3D whole-space response characteristic of the sheet conductive body located in uniform medium has been imitated with a magnetic dipole,and adopting non-uniform grid and time step length,the 3D time domain finite-difference formula has been deduced,the contour figure of the magnetic field and itshave also been plotted on the basis of the data obtained at quite a few surveying points.The diffused regularity of the transient field,the characteristic of the field affected by roadway and boundary plane was analysised in detail.The results showed that diffused velocity of the transient field reduced and its attenuation slowed down,when magnetic field passing through the boundaryplane between the sheet conductive body and the earth;and as the iterative number increasing,a ring-contour shaped at the center of the sheet conductive body;the effect of laneway was obvious at early time and feeble at late time.The objectives are to provide interpretation guidelines for the whole-space TEM anomalies.