Two dimensional interpretation of 3-D magnetotelluric data: an example of
limitations and resolution
Ledo, J., P. Queralt, A. Marti and A.G. Jones
Interpretation of magnetotelluric (MT) data for three-dimensional (3-D) regional conductivity
structures remains uncommon, and two-dimensional (2-D) models are often considered an adequate
approach. In this paper we explore 2-D interpretation of 3-D data by considering the synthetic responses
from several profiles over a 3-D structure chosen specifically to highlight the advantages and
limitations of 2-D interpretation. We obtain 2-D models from inversion of the synthetic 3-D data
set with different conditions (noise and distortion) applied to the data. We demonstrate the importance
of understanding galvanic distortion of the data and show how 2-D inversion is improved when the regional
data are corrected prior to modelling. When the 3-D conductive structure is located below the profile,
the models obtained suggest that the effects of finite strike are not significant if the structure has a
strike extent greater than about one-half of a skin depth. In this case the use of only TM-mode data
determined better the horizontal extent of the 3-D anomaly. When the profiles are located off the 3-D conductive
structure the use of only TM-mode data can imagine phantom conductive structures below the profile, in this
case the use of both polarizations produced a better determination of the subsurface structures.
It is important to note that the main structures are identified in all the cases considered here, although
in some cases the large data misfit would cause scepticism about features of the models.
Geophysical Journal International, , accepted, 23 January 2002.
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Alan G Jones / 10 June 2004 /