ELECTRICAL ANISOTROPY IN THE LOWER CRUST OF BRITISH-COLUMBIA - AN INTERPRETATION OF A MAGNETOTELLURIC PROFILE AFTER TENSOR DECOMPOSITION

The application of a magnetotelluric (MT) tensor decomposition scheme to the long period responses of the BC87 data set yields an almost two-dimensional regional conductivity structure with a strike of N45-degrees-E. The main feature in the MT responses of the observed region are diverging apparent resistivity curves and phase differences. 1-D modelling and 2-D inversion of different combinations of these MT parameters suggest the existence of a strongly anisotropic layer in the middle to lower crust. Based on the 1-D estimates for resistivities, and using the geometry from the 2-D inversion, a 2-D forward model is derived which includes a strongly anisotropic layer at 30 km depth with the two principal resistivities of 300 OMEGAm and 5 OMEGAm. This model explains mainly the phases of the impedance tensor at longer periods. The apparent resistivities are affected by small-scale, near surface inhomogeneities.