THE BC87 DATASET - APPLICATION OF HYPOTHETICAL EVENT ANALYSIS ON DISTORTED GDS RESPONSE FUNCTIONS AND SOME THIN SHEET MODELING STUDIES OF THE DEEP-CRUSTAL CONDUCTOR

Galvanic distortion of the regional MT responses was inferred from the analyses of the BC87 dataset presented at the MT-DIW1 in 1992. Since perturbation currents also produce an anomalous magnetic field, the GD S response functions were suspected to be distorted in the long period range. In order to reveal the correct regional strike direction, hypo thetical event analysis was applied to the data from all sites. With t his technique, common regional information, such as strike and impedan ce phase, can be recovered from distorted response functions. Although the BC87 GDS data. are noisy, and the distortion is more of an induct ive than of a purely galvanic nature, the resulting regional strike di rection of 60 degrees agrees well with the azimuth suggested from prev ious MT decomposition methods. Thin sheet modelling studies of the geo metry of the deep crustal conductor (L-shaped or oblique) at 1000 s im ply that along the BC87 profile induction arrows are generally produce d by current concentrations around a resistive region associated with the Nelson Batholith. Comparison of the model induction arrows with th ose determined from the BC87 data indicates that the model featuring t he oblique, NE striking conductor (SABC) may be favoured.