Abstract: The delectability of transient electromagnetic method (TEM) to multiple 3D conductive sheets with valley topography is discussed in detail in the paper. An anomalous body with a resistivity of 10⁶ohm.m is designed to simulate the valley topography. The results of the modeling illustrate that the total anomalous fields are the summation of anomalous fields produced by the valley and the conductive sheets. The delectability of TEM to the conductive sheets buried shallower beneath the receivers is quite good without valley topography and TEM is much more sensitive to anomalies near the source than those far from the source. It is interesting that the total field will enlarge the anomalies fields of those conductive sheets placed in far source when the valley topography exists and, in some sense, this will be helpful for TEM to detect the anomalies from far source. The delectability of TEM will become weaker when the distance between two anomalous bodies is too small. In general, the delectability of TEM to multiple 3D conductive sheets is still good when valley topography exists.

Key words: topography, forward modeling, transient electromagnetic responses, anomalous bodies

摘要： 以层状地层中的2个三维导电薄板为例,考虑了山谷地形存在时,瞬变电磁法(TEM)分辨地下多个三维异常体的能力。模型计算的结果表明,当有山谷地形存在时,总的异常场由薄板的异常和地形的异常叠加在一起,表明异常场在空间上具有可加性质。在地形平坦时,TEM方法对相同尺寸的近源异常体的分辨能力要优于远源,而且离源越远的异常体异常越小,最后直到无法分辨。但是当存在山谷地形并且把源放在其中时,它们的总异常场叠加后会“放大”远源异常体的异常场,在一定意义上说,这对于分辨远处的异常体更加有利。当异常体在接收器下方埋深不是太大时,不论山谷地形在源处还是接收器处,TEM法对这些异常体的探测能力都是比较好的。2个异常体相距太近时,其异常会叠加在一起,给TEM的分辨增加一些困难。总体表明,在有山谷地形存在时,TEM方法对多个异常体仍具有较好的探测能力。

关键词: 地形, 正演, 瞬变电磁响应, 异常体