1‐D Forward Modeling of the CSAMT Signal Incorporation IP Effect

Abstract

AbstractThe response of a geological object to an exciting source of electromagnetic (EM) waves in the frequency domain is the integrated one of EM induction and induced polarization. In the forward and inversion modeling of the conventional CSAMT method, telluric resistivity is assumed to be a real number unrelated to frequency. It is, however, actually a complex number associated with frequency because of the induction polarization (IP) effect. The purpose of this work is to promote the study on the integrated response above mentioned, expand the application area of the IP method and enhance the precision of EM exploration. Based on the Dias model, using complex resistivity to replace direct current resistivity which does not incorporate IP effect, we have made forward simulation of a CSAMT field source on a 1‐D layered model to offer the theoretical basis for extracting the IP information in CSAMT signal. The result shows that the response curves of apparent resistivity and phases (including the far field, transitional field, and near field) have obvious abnormal changes due to incorporation of the IP parameter. The peak anomalies of amplitude ratios and phase differences before and after polarization can exhibit IP anomalies in a direct view. These peak values have a continuous correlation with the polarized layer thickness, buried depth and variations of resistivity. It demonstrates that extracting IP information from EM signals in the frequency domain has a bright prospect.