This paper considers the method of interpretation of, and results from, magnetotelluric soundings when integrated with data from magnetometry, gravimetry, and other geological and geophysical data. Stress is placed on incorporating the shift effect and the 3-D coast effect, which was studied in tentative models using numerical modeling of the magnetotelluric field. The interpretation is based on longitudinal curves, which are less subject to distortions at low frequencies. Transverse curves were used to obtain more accurate resistivities in the upper section and to identify faults. Longitudinal MTS curves were inverted to derive a geoelectric section that characterizes the resistivities in the sedimentary-volcanogenic cover and in the underlying rocks. The Earth's crust contains a conductive layer that lies at varying depths, between 30 and 15 km. We discuss a possible origin for crustal resistivity anomalies and their possible relationship to ore occurrences at the ground surface.
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