The role of displacement currents in transient electromagnetic soundings

Аннотация

The electrical prospecting by the transient electromagnetic sounding method (TEM) employs a set of the established notions. For example, it is believed that the effect of the displacement currents on the results of TEM is typically negligible except for the techniques which are intended for exploring the uppermost portions of the section and use high frequencies. In other words, for the underlying physicomathematical description, it is sufficient to use a quasi-stationary approximation. This is true for the traditional methods; however, the studies and results presented in this paper show that these notions need to be revised when TEM soundings are viewed from a more general standpoint. The suggested approach to the problem of the displacement currents’ influence on TEM soundings consists in the fact that the question should be partitioned into several issues and the shallow-depth electric prospecting which employs the high frequencies (or very short transient times) should be considered separately. The problem should be viewed from the standpoint of using the TM (transverse magnetic) and TE (transverse electric) polarizations of the electromagnetic field. As the core of this paper, I suggest the new and, in my opinion, rather fascinating results showing that the displacement currents can be in principle vital for the deep electrical prospecting studies; however, this is the case only if a pure TM field is used.