Abstract: The tipper vector,a significant parameter in magnetotelluric(MT) sounding,is applicable to infer fault structures that cause lateral inhomogeneity of media.Subsurface faults typically exhibit three-dimensionality and complexity.To reveal the MT tipper response characteristics in 3D fault models,this study conducted numerical simulations of the MT tipper response in 3D fault models based on the vector finite element method.First,the validity of the 3D tipper forward modeling program was verified through theoretical model calculations and comparisons with previous finite element results.Subsequently,four typical 3D models for vertical,normal,reverse,and strike-slip faults were employed for forward modeling,obtaining the response characteristics of the real part,imaginary part,amplitude,and phase of the tipper.The simulation results are as follows:(1) In two polarization modes,the response characteristics of the real part,imaginary part,and amplitude of the tipper effectively reflect the properties,strikes,and dip directions of the four different faults while indicating the location of the laterally inhomogeneous boundaries,thus serving as a significant basis for discriminating fault types and characteristics;(2)In contrast,the relatively complex response characteristics of the phase fail to effectively mirror the fault characteristics.