Two-Dimensional Magnetotelluric Tipper and Apparent Tipper：Simulation and Application

In order to analyze abnormal responses of 2D magnetotelluric tipper data, a tipper data forward calculation was developed using the finite element quadrilateral mesh, and a forward numerical simulation of the abnormal body, inclined faults, static effects, and terrains was made based on their theoretical models. The derivation and calculation of the apparent tipper data were improved, and the tipper and apparent tipper were compared. As an application example, the apparent tipper was calculated using the transversal electric (TE)-mode apparent resistivity and phase data during the audio-magnetotelluric (AMT) exploration of the Zhongyi tunnel on the newly built Lijiang-Shangrila railway. The results show that the tipper can reflect the abnormal lateral boundary and fault apparently, and is only affected by the static displacement and topography at mid-high frequency band above 1 Hz, where the tipper and apparent tipper data have a good correspondence. In addition, the apparent tipper data can not only locate the fracture zone of the tunnel and reflect the position, scale, and trend of main faults effectively, but also can reflect the more subtle abnormal structures.