The relationship between the magnetotelluric tensor invariants and the phase tensor of Caldwell, Bibby and Brown

In recent papers Caldwell, Bibby and Brown (2002, 2003) (hereafter referred to as CBB) have introduced a new and elegant method for analysing magnetotelluric (MT) data which can be applied directly to galvanically distorted data in a regional conductivity structure of any dimension. It is therefore more general and direct than previous methods (e.g. Bahr, 1988; Groom and Bailey, 1989; Smith, 1995) which involve a decomposition of the MT tensor based on the assumption that the regional conductivity structure is 2D. The procedure of CBB, on the other hand, is founded on their innovative definition of a real 2 × 2 ‘phase tensor’ which is independent of any real (galvanic) distortion that may be present (in fact it is identical for both the distorted and the regional data), and does not require any assumption about the dimensionality of the underlying regional conductivity.