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 ele ment forward modelling with the concepts of rapid relaxation inversion of m agnetotelluric data. The inversion uses the same technique to compute sensi tivities as the rapid relaxation inversion, and these approximate sensitivi ties are validated by comparison with exact 2.5-D sensitivities. The compar ison shows that the approximate sensitivities are similar in shape to the e xact sensitivities when transmitter-receiver offsets are greater than one s kin 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.