Publication 17
Statistical evaluation of MT and AMT methods applied to a basalt-covered area in south-eastern Anatolia, Turkey
O.M. Ilkisik and A.G. Jones
Abstract
The effïcacy of the magnetotelluric and audiomagnetotelluric (MT/AMT) methods for
detailing the structure of a hypothetical geological section is investigated by using the singular
value decomposition (SVD) technique. The section is representative of southeastern
Turkey, which is mostly covered by basalt and is a prime area for oil exploration. One of the
geological units, the Germav shale at a depth of 600 m, is a problem layer for electromagnetic
surveys because of its very low resistivity (on average 3 Qm) and highly variable thickness
across the area (200-900 m). In the MT frequency range (0.000440 Hz) its total
conductance-or, since its resistivity is known from resistivity log information, its thicknessis
the best resolved model parameter. The total depth to the Germav shale and the resistivity
of the Cambrian/Precambrian basement are the marginally resolved parameters. In the AMT
frequency range (410 O00 Hz) the resistivity of the surface basalt layer strongly affects the
resolution of the other, less important, model parameters which are the total depth to the
Germav shale and the total conductance of the Germav shale. The errors in the measurements
determine the number of model parameters resolvable, and are also important for
interpretation of the geological model parameters to within a desired accuracy.
It is shown that statistical evaluation of the MT andfor AMT interpretations by using an
SVD factorization of the sensitivity matrix can be helpful to define the importance of some
particular stage of the interpretation, and also provides a priori knowledge to plan a proposed
survey. Arrangements of MT and AMT observations, together with some Schlumberger
resistivity soundings, on a large grid will certainly provide three-dimensional detailed
information of the deep geoelectric structure of the area.
Source
Geophysical Prospecting, 32, 706-724, 1984.
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Alan G Jones / 7 October 2007 /
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