Removing Galvanic Distortion in 3D Magnetotelluric Data Based on Constrained Inversion.

The galvanic distortion caused by small-scale electrical inhomogeneities near the shallow surface perturbs the overall frequency response curve of magnetotelluric (MT) records and adversely affects the imaging of deep electrical structures. Various efforts have been made to suppress the galvanic distortion, but they are still difficult to use in complex regional structures. To effectively recover the deeper electrical structures, we develop an inversion technique in which the shallow electrical structures are constrained by other types of electromagnetic data and used as part of the prior model to remove the galvanic distortion. When other types of electromagnetic data are unavailable, we can also simulate the galvanic distortion by using a refined forward mesh and putting small-scale electrical resistivity anomalies beneath the surface. We validate our inversion approach using synthetic examples and apply it to field MT data collected from the northern Trans North China Orogen. A three-dimensional electrical resistivity model is obtained based on the prior model designed according to the locations of distorted MT stations. In our resulting model, artifacts caused by galvanic distortion are removed as compared to previous work. We demonstrate that our method is effective in improving the reliability of MT inversions in complex regions, leading to better interpretations of deep electrical structures. [ABSTRACT FROM AUTHOR]