Body-growth inversion of magnetic data with the use of non-rectangular grid

• We presented a magnetic version of body-growth inversion.
• The subsurface is divided by non-rectangular grid into finite elements.
• Sensitivity matrix is integrated by using Gauss–Legendre quadrature.
• It offers fine representation of complicated relief and subsurface structure.
• Forcing positive magnetic susceptibility is readily implemented.

Recently, inversion of magnetic data to recover a distribution of magnetic susceptibility has been widely used for mineral exploration and other problems. However, the commonly used grid-based techniques have some practical difficulties, namely, degraded resolution with depth, increased computational cost with the size of the problem, and the influence of regional field. Especially, most of inversion techniques employ rectangular grid for division, which is inconvenient to represent complicated magnetic structure and actual topography.We presented the magnetic version of body-growth inversion method with the use of non-rectangular grid. Essentially, this method is a new implementation scheme of 2-D and 3-D magnetic inversion, inherited from the gravity inversion by means of growing bodies, previously developed. For simple modification, we adopt non-rectangular grid to divide the subsurface region into a set of isoparametric finite elements rather than the commonly used rectangular grid of prismatic cells. This allows a better representation of actual topography and complicated magnetic structure in forward modeling. Additionally, the calculations of magnetic field and sensitivity matrix are implemented by the Gauss–Legendre quadrature rather than analytic formulae.We tested the method by using synthetic data for two 2-D and three 3-D models and applied it to field data. Resultantly, we conclude that the method has some advantages such as: better representation of actual topography, automatic imposing of the positive magnetic susceptibility, and possibility to separate the regional field and remove its effect to inversion result. Thus, it seems to be a better alternative to the traditional grid-based techniques when inverting local bodies with complicated shapes under mountainous terrain.