The Voisey's Bay area, in northern Labrador, presents unusual problems in the interpretation of audiofrequency magnetotelluric data. The survey area is located between two east-oriented fjords; the sea-water filling these is assumed to have a resistivity of about 0.3 ohm.m. This is in strong contrast toi the resistive Proterozoic metamorphics underlying the survey area, which have resistivities in the range 10,000 to 100,000 ohm.m. Thus, the sea-water interface can be expected to have a major impact on measurements. In addition, recent sediments occur in minor pods along drainages and near lakes, and these again cause significant AMT responses. Previous work (e.g. Mackie and Watts, 1999) has modeled the gross effect of the sea, and Balch et al. (1998) presented a comparison between AMT and AEM surveys over the same area. In this paper, we show how the use of AEM data to quantify the resistivity and extent of shallow conductors improves the numerical interpretation of AMT data.
CSEM can provide oil companies with information on rock resistivity before drilling a well. We present a CSEM interpretation workflow based on anisotropic 3D inversion applied to a dataset acquired offshore west of Greenland. We show how the method can give complementary information on the resistivity properties. Integrated with seismic and geological knowledge, this allows high-grading prospective leads, detection of resistivity features such as volcanics or shallow basement, and provides evidence of possible resistivity anisotropy.
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