Sensitivity Patterns for Features of MT Response Functions and Their Application to Inversion

Abstract

Summary The measured electromagnetic fields in the magnetotelluric (MT) survey are converted into various MT response functions, which are used as the input of inversion. Inversion results are dependent on the input MT response functions. We examine characteristics of the major MT response functions (impedance, apparent resistivity, and tipper) in inversion using their sensitivity patterns. The sensitivity patterns show that xx- and yy-components of the impedance are suitable for 3D inversion; xy- and yx-components of the impedance and apparent resistivity are useful for inversion of 2D structures whose strikes are along the y- and x-axes, respectively; and the tipper can be helpful in imaging both 2D and 3D structures. Through the synthetic examples and case study, we show how to apply the sensitivity patterns for inversion. In the synthetic examples for 2D interpretation of MT data, the features of the sensitivity patterns of the tipper contribute to imaging of a 2D structure for a specific receiver array where receivers right above the 2D structure are not available. In the case study, we show that the strategy of selecting optimal MT response functions developed by considering the situation of MT survey and the sensitivity patterns improves inversion results.