3:00 PM - 3:15 PM
[SEM12-06] Applicability evaluation of non-conforming deformed hexahedral mesh for marine magnetotellurics
Keywords:magnetotelluric inversion, non-conforming mesh, finite element method, electrical resistivity structure
Topographic distortion is a major problem in magnetotelluric modeling and interpretation. Especially, observed data of ocean magnetotelluric surveys can be affected by large-scale bathymetry and land-ocean distribution as well as smaller-scale seafloor undulations around observation sites. Some modeling approaches have been proposed to overcome the problem. However, a previously developed inversion approach based on the finite difference method shows the model recovery depends on the prior and initial models. Although the inversion using an unstructured tetrahedral finite element mesh is another effective approach to deal with topographic distortion, it requires a substantial effort to include global-scale land-ocean distribution. Therefore, I made a magnetotelluric inversion code using non-conforming deformed hexahedral mesh to incorporate both large-scale bathymetry and smaller-scale seafloor undulations effectively in the electrical resistivity modeling. The non-conforming hexahedral mesh allows us to make small elements only around observation sites, where smaller-scale undulations need to be represented. Besides, the developed inversion code does not use the prior model because the Laplacian of logarithms of subsurface electrical resistivities is used as the regularization term. I confirmed that, for a sinusoidal seafloor model, the forward calculation using a non-conforming deformed hexahedral mesh gives the apparent resistivity, phase, and vertical magnetic transfer function close to their analytical solutions. Furthermore, a synthetic inversion test demonstrates that the developed inversion code can recover the original electrical resistivity structure.