Adaptive regularization joint inversion of marine CSEM and MT data in vertically anisotropic stratified structures

In inversion and interpretation of industrial EM data sets, it can be sufficient in a number of situations by assuming isotropy, however, the presence of electric anisotropy in the earth' s crust, due to thin layer interbedding or grain alignments in the sediments can significantly alter the response measured in the EM receiver. Ignoring anisotropy in interpreting marine CSEM data may lead to a distorted image of seabed conductivity structures, even misinterpretation. We present a joint inversion method for frequency domain marine CSEM data and MT data in vertically anisotropic stratified media. The inversion approach is based on the Gauss-Newton scheme. Due to the influence of ocean currents, the transmitter antenna will appear tilting and rotating. Applying superposition principle of electromagnetic field, we extend the scheme of Loseth and Ursin (2007) for calculating CSEM fields from a horizontal dipole source (HED) and/or a vertical dipole source (VED) in stratified media with vertical anisotropy to the general case of arbitrary orientation dipole source. The partial derivatives of the electromagnetic fileds (CSEM data) with respect to both the horizontal and vertical resistivity and apparent resistivity (MT data) with respect to the horizontal resistivity are analytically calculated. Based on the relationship between the horizontal resistivity and the vertical resistivity of the inversion model, an adaptive selection method for regularization factors is proposed to balance the effects of the data misfit and the structural constraint.