Effects of galvanic distortion on magnetotelluric data over a three-dimensional regional structure |
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Authors: | Juanjo Ledo Pilar Queralt & Jaume Pous |
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Institution: | Departament de Geologia Dinàmica, Geofísica i Paleontologia, Universitat de Barcelona, Martíi Franqués s/n, 08028 Barcelona, Spain. E-mail: |
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Abstract: | Although the galvanic distortion due to local, near-surface inhomogeneities is frequency-independent, its effect on the magnetotelluric data becomes, in a 3-D structure, frequency-dependent. Therefore, both the apparent resistivity and the phase responses are disturbed, and a correction should be carried out prior to the 3-D interpretation in order to retrieve the 3-D regional impedance tensor. In many cases, the structure is 2-D for depths corresponding to a first range of periods and 3-D for longer periods (called 2-D/3-D). For these cases, a simple method which allows us to retrieve the 3-D regional impedance tensor (except the static shift) is presented. The method proposed uses the Groom & Bailey decomposition of the distortion matrix for the short periods. Three examples are presented: two using synthetic data and one employing real data. These examples show the effect of the galvanic distortion over a regional 2-D/3-D model and the retrieval of the regional transfer functions from the distorted ones. |
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Keywords: | electrical resistivity magnetotellurics structural dimensionality tensor decomposition |
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