The real and imaginary parts (or amplitude and phase) of physically realizable transfer functions are explicitly related by the integral dispersion relation (DR). Application of the DR is especially effective in the magnetotelluric (MT) method, since it allows to increase the data quality, correct the biased estimations of the impedance tensor and other transfer functions, detect the inconsistent data, etc.

Unfortunately, the DR could be violated in some geoelectrical situations (namely, over curved 3D conductors, strongly anisotropic bodies, and for the off-shore MT measurements), which dramatically reduces its practical value. We show that such violations have very specific nature and thus could be distinguished from those caused by inconcistent or noisy data. Furthermore, it turns out that by careful choice of the appropriate kind of relation and appropriate transfer function the DR applicability may be extended to the data obtained virtually at any MT site irrespective of the geoelectrical circumstances.