Two-dimensional Magnetotelluric Inversion with Electrical Anisotropy and Its Application in the Northern Tibetan Plateau

Electrical anisotropy exists at all scales in earth. Identifying electrical anisotropy contributes to understanding of the physical state in depth, deformable environment and dynamic models within the Earth. In this study, based on the realized finite-difference magnetotelluric forward algorithm considering arbitrary electrical anisotropy, we construct the objective function for anisotropic inversion and calculate its value and gradient. Then, we complete the anisotropic magnetotelluric inversion algorithm with mature non-linear conjugate gradient inversion technology. A two-dimensional synthetic model is used to exam the stability of the inversion algorithm. The synthetic examples directly show the difficulty in recovering vertical resistivity. And, the elements of conductivity tensor should be considered simultaneously as a whole in the anisotropic interpretation. Along a magnetotelluric profile across the east Kunlun to the west Qaidam Basin in northern Tibetan Plateau, the previous two-dimensional isotropic inversion results have imaged a low resistive anomaly in the uppermost mantle beneath Qiman Tagh range. An apparent azimuthal anisotropy structure appears at the same place in the anisotropic inversion results. The shear direction indicated by the minimum principal resistivity is not parallel to the surface orogenic belt, which implies that, in addition to the control of the collision of India-Eurasia plate, the stress environment is possibly affected by left-lateral shear in the strike-slip Altyn Tagh Fault.