Rapid relaxation inversion of CSAMT data

In this paper an inversion algorithm for controlled-source audio frequency magnetotelluric data is presented. This algorithm combines 2.5-D finite element forward modelling with the concepts of rapid relaxation inversion of magnetotelluric data. The inversion uses the same technique to compute sensitivities as the rapid relaxation inversion, and these approximate sensitivities are validated by comparison with exact 2.5-D sensitivities. The comparison shows that the approximate sensitivities are similar in shape to the exact sensitivities when transmitter–receiver offsets are greater than one skin depth in the Earth. The magnitudes of the two sensitivities differ but the variations with depth are similar. Tests of the algorithm on synthetic data and field data provide promising results.