The full-field apparent resistivity of CSAMT defined by the magnetic field y-component and an application to a geological survey in the Xiong'an New Area, China

Controlled source audio magnetotelluric (CSAMT) has good depth penetration and high data quality. However, the Cagniard apparent resistivity calculated in the near-field zone and transition zone is distorted, and collecting electric field components in some specific landscapes requires a high cost, such as desert, permafrost, and water areas. The magnetic field y-component (Hy) is not restricted by bad electrode grounding conditions, and the signal level is greater than that of the magnetic field z-component (Hz), which can be used to obtain the ground resistivity. A simple algorithm was used to calculate the apparent resistivity defined by Hy, and the response characteristics and measurement range were analysed by model calculation. The results show that the Hy full-field apparent resistivity has no obvious distortion. This method is applied to geological surveys in the Xiong'an New Area, China. The results indicate that the detection depth of the Hy full-field apparent resistivity is better than that of electric field x-component (Ex), and the signal-to-noise ratio is better than that of Hz. Moreover, the 1D and 2D inversion results are in good agreement with the known geological conditions. This method can extend the observational conditions and range of CSAMT.