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.
