The application of audio magnetotelluric for 3D geological mapping in the Gobi Desert area. (18th August 2019) - Liu, Ying
Abstract : Constructing the strata and bedrocks beneath the overburden for three‐dimensional (3D) geological mapping in the Gobi Desert area is challenging but necessary. Rock resistivity is a key parameter to research the underground media. In the Gobi Desert area, the overburden has low resistivity, while the underlying strata and bedrocks have much higher resistivity in general. These features provide the basic conditions for distinguishing the rocks by their resistivities. The audio magnetotelluric (AMT) method is effective for investigating the electrical structure of most upper crust. Due to minor anthropogenic electromagnetic interference, good data can be easily acquired by reducing the ground resistance and by placing a remote reference station in the Gobi Desert area. WAL analysis and phase tensor method, derived from impedance tensors, can indicate the dimension of a structure, which in turn suggests whether a two‐dimensional or 3D inversion needs to be used. The resistivity distribution obtained via inversion can be translated to lithological units associated with rock resistivity measurement. Combined with borehole constraint, the strata and bedrocks beneath the overburden could be explicitly described. By application of AMT, the Quaternary and Tertiary strata could be divided in the Barkol Basin by a low‐resistivity layer, which was attributed to saturation with salty water. The Eocene and Jurassic strata were distinguished in the Hami Basin by 10‐ and 50‐Ωm contour lines, respectively. In both areas, high‐resistivity bedrocks were clearly depicted.