Two-dimensional joint inversion of magnetotelluric and dipole-dipole resistivity data

This paper describes 2-D joint inversion of MT and dipole-dipole resistivity data with the emphasis on the computer algorithm. The algorithm produces a 2-D model composed of a large number of rectangular blocks, each of which has constant resistivity. The solutions to two forward problems are based on the finite-element method. The computation time for the partial derivatives of MT responses is reduced by using the reciprocity relation and the concept of a fictitious source. The smoothness-constrained least-squares method, together with the modified Gram-Schmidt method, is also used to stabilize the solution and avoid spurious resistivity features. Synthetic and field data examples show that the 2-D joint inversion can be effective for improving the resolution attained by the 2-D interpretation of a single kind of data set.