Augmented electrical resistivity tomography magnetotelluric response function

Abstract

With the magnetotelluric (MT) method, conductive layers can mask deeper resistors. An analytical relationship is derived between electrical resistivity tomography (ERT) and MT data to calculate an augmented ERT-MT response function. The augmented ERT-MT response function adds additional high-frequency content in the MT response function. This allows us to model the near-surface conductive layer from the ERT data and resolve deeper resistive structures with the MT data. In general, for the 1D case, the augmented ERT-MT response function results in a 1D inverse model that demonstrates an improvement of up to approximately 91% in recovering the true resistivity model. The augmented ERT-MT response function also is tested on theoretical 2D models. Two electrical resistivity models are used for the 2D tests. For both 2D models, the resistive dike and conductive overburden that were initially concealed are recovered when using the augmented ERT-MT response function. The augmented ERT-MT response function also is applied to field data, allowing us to map a resistive dike below a conductive overburden that was absent in the standard MT inverse model. The recovered dike and fault zone in the augmented ERT-MT response function resistivity inverse model correlate with the same features observed in a magnetic susceptibility inverse model. The augmented ERT-MT response function technique improves the resolution of MT to recover resistors beneath a conductive layer for the theoretical and experimental cases.