Pseudo-Magnetotelluric 2D Inversion Technology of Magnetic-Source Transient Electromagnetics

Based on the fact that it is difficult to implement optimum inversion using 2D and 3D forward modeling with magnetic-source transient electromagnetics (TEM), this paper explores a novel approach to the implementation of 2D magnetic-source TEM inversion. In particular, we converted magnetic-source TEM data into magnetotelluric (MT) data and then used a 2D MT inversion method to implement a 2D magnetic-source TEM inversion interpretation. First, we studied the similarity between magnetic-source TEM waves and MT waves and between magnetic-source TEM all-time apparent resistivity and MT Cagniard apparent resistivity. Then, we selected an optimal time–frequency transformation coefficient to implement rapid time–frequency transformation of all-time TEM apparent resistivity to MT Cagniard apparent resistivity. Afterward, we conducted 1D pseudo-MT inversions of magnetic-source 1D TEM theoretical models. The 1D inversion results demonstrated that the difference between the inversion parameters and model parameters was small, while the MT 1D inversion method could be used to conduct magnetic 1D TEM inversion within a certain margin of error. We further conducted 2D pseudo-MT inversions of 3D magnetic-source TEM theoretical models, and the 2D inversion results indicated that selecting a joint 2D pseudo-MT transverse-electric (TE) and transverse-magnetic (TM) inversion method based on measuring the line above a 3D anomalous body can help to accurately implement a 2D inversion interpretation of the 3D TEM response.