Effects of galvanic distortions on magnetotelluric data: Interpretation and its correction using deep electrical data |
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| Authors: | Jimmy Stephen S G Gokarn C Manoj S B Singh |
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| Institution: | (1) National Geophysical Research Institute, # 66, 500 007 Hyderabad, India;(2) Indian Institute of Geomagnetism, Colaba, 400 005 Mumbai, India |
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| Abstract: | The non-inductive galvanic disturbances due to surficial bodies, lying smaller than high frequency skin depth, cause serious
interpretational errors in magnetotelluric data. These frequency independent distortions result in a quasi-static shift between
the apparent resistivity curves known as static shift. Two-dimensional modelling studies, for the effects of surficial bodies
on magnetotelluric interpretation, show that the transverse electric (TE) mode apparent resistivity curves are hardly affected
compared to the transverse magnetic (TM) mode curves, facilitating the correction by using a curve shifting method to match
low frequency asymptotes. But in the case of field data the problem is rather complicated because of the random distribution
of geometry and conductivity of near surface inhomogeneities. Here we present the use of deep resistivity sounding (DRS) data
to constrain MT static shift. Direct current sensitivity studies show that the behaviour of MT static shift can be estimated
using DC resistivity measurements close to the MT sounding station to appreciable depths. The distorted data set is corrected
using the MT response for DRS model and further subject to joint inversion with DRS data. Joint inversion leads to better
estimation of MT parameters compared to the separate inversion of data sets. |
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| Keywords: | Magnetotelluric deep resistivity sounding galvanic distortion static shift joint inversion |
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