## 5 Results of MT Profile Experiment  
In order to verify the effect of the MRR method, we arranged an MT survey line (AA') from Matou Town, Zhuozhou City, to Liujie Township, Yongqing County, Langfang City (Figure 1). This survey line passes along the BGHSR, Beijing-Jiujiang Railway and Beijing-Xiong'an Intercity Railway and through densely populated cities such as Zhuozhou and Gu'an. Human interference of various types is particularly strong. In order to reduce the influence of cultural noise, the positions of some sites are offset at a certain distance according to the surrounding interference. The distance between the stations is approximately 1 km. There are a total of 60 stations with a total length of approximately 60 km. In this area, much exploration work has been done for many years. Figure 8a shows a known seismic survey profile near AA'. Many deep wells have been drilled. This enables us to gain a deeper understanding of the cap layer structure and base structure of the area. Figure 7: Plots of apparent resistivity and phase data of station 2. Red curves denote the single station (ss), blue curves denote nocturnal data (nd), magenta curves denote station 8 as a remote reference (RR8), green curves denote station 7 as a remote reference (RR7), and black curves denote stations 7 and 8 as remote references (MRR7&8). (**a**) Comparison of ss and MRR. (**b**) Comparison of nd and MRR. (**c**) Comparison of RR7 and MRR. (**d**) Comparison of RR8 and MRR. Figure 8: Comparison diagram of the inversion results for profile AA\({}^{\prime}\). (**a**) Seismic profile near AA\({}^{\prime}\). (**b**) The 2D inversion result of the MRR (7 and 8). (**c**) The 2D inversion result of the SS. We used the impedance tensor decomposition technique for the profile data and calculated the direction of the electrical principal axis. After rotating the impedance tensor towards the geo-electric strike direction, the data of the transverse electric (TE) and traverse magnetic (TM) modes were obtained. The nonlinear conjugate gradient method (NLCG) implemented in WinGlink software was used for two-dimensional inversion [36]. The frequency range we used was 433-0.001 Hz. First, the poor-quality data were removed, and then the 2D inversion of the TM, TE and TM + TE modes of the apparent resistivity and impedance phases were performed [37; 38]. The initial model was constructed with a uniform half-space of 100 \(\Omega\)m. The data were inverted with the regularization parameter \(\tau\) = 10. The inversion results of the three modes were analyzed by referring to the geological and geophysical information of the survey area. Finally, the TM + TE mode inversion result was selected because it was more consistent with the actual geological conditions. The inversion of the MRR data was completed with an RMS misfit of 2.34 after 99 iterations. The inversion of the SS data was completed with an RMS misfit of 2.24 after 103 iterations. In general, a sharp change in resistivity is often a sign of fracture or lithologic interface, where a slow change corresponds to a stable and uniform electrical layer. Therefore, the image of the contoured resistivity section can reflect the distribution law of the resistivity of the underground half-space medium along the survey line, that is, the electrical structure model of the profile. Figure 8b is a two-dimensional inversion section based on data with MRR, which clearly shows the lithologic units. From west to east, it corresponds to the Beijing sag, Daxing uplift, Langgu sag, Niutuo uplift and Baxian sag. The upper part of the section, where the resistivity value is very low and uniform, is exactly the Langgu and Baxian sag, where the Cenozoic deposits are very thick. The resistivity value also reflects the shallow-buried Daxing and Niutuo uplifts. Figure 8a is a seismic section very close to AA' [26; 39], and the average wave speed is approximately 3000 m/s. It shows that the reflected underground structure is almost the same as that in Figure 8b.