Three-dimensional galvanic distortion of three-dimensional regional conductivity structures: Comments on "Three-dimensional joint
inversion for magnetotelluric resistivity and static shift distributions in complex media" by Y. Sasaki and M.A. Meju (2006).
Alan G. Jones
In their paper, Sasaki and Meju  describe their approach to 3-D inversion of MT data for 3-D
structure taking galvanic distortion, which they characterize and simplify as static shifts, into account.
The purpose of this comment is to draw attention to the fact that their approach is valid only in two very restrictive cases; either that the structures are 2-D (which begs the question as to why 3-D inversion is being undertaken) or in the unlikely case that the distortion at every observation site is such that there are only statistically significant values on the diagonal elements of the distortion tensor, and the off-diagonal distortion elements are statistically zero.
In addition, this Comments draws attention to the point that one cannot adopt a technique routinely applied in 2-D inversion of MT data to deal with static shifts, namely to set large errors floors on the apparent resistivities, as the phases are also distorted from their true regional values.
Journal of Geophysical Research - Solid Earth, 116, B12104, doi: 10.1029/2011JB008665.
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Alan G Jones / 19 December 2011 /