Publication 185
The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and inter-station
horizontal magnetic transfer function data: Results from a synthetic case study
Campanya, J., X. Ogaya, A.G. Jones, V. Rath, J. Vozar, and N. Meqbel
Abstract
As a consequence of measuring time variations of the electric and the magnetic field,
which are related to current flow and charge distribution, magnetotelluric (MT) data in
two dimensional (2-D) and three dimensional (3-D) environments are not only sensitive
to the geoelectrical structures below the measuring points but also to any lateral
anomalies surrounding the acquisition site. This behaviour complicates the
characterisation of the electrical resistivity distribution of the subsurface, particularly in
complex areas. In this manuscript we assess the main advantages of complementing the
standard MT impedance tensor (Z) data with inter-station horizontal magnetic tensor (H)
and geomagnetic transfer function (T) data in constraining the subsurface in a 3-D
environment beneath a MT profile. Our analysis was performed using synthetic
responses with added normally distributed and scattered random noise. The sensitivity of
each type of data to different resistivity anomalies is evaluated, showing that the degree
to which each site and each period is affected by the same anomaly depends on the type
of data. A dimensionality analysis, using Z, H and T data, identifies the presence of the
3-D anomalies close to the profile, suggesting a 3-D approach for recovering the
electrical resistivity values of the subsurface. Finally, the capacity for recovering the
geoelectrical structures of the subsurface is evaluated by performing joint inversion
using different data combinations, quantifying the differences between the true synthetic
model and the models from inversion process. Four main improvements are observed
when performing joint inversion of Z, H and T data: (1) superior precision and accuracy
at characterising the electrical resistivity values of the anomalies below and outside the
profile; (2) the potential to recover high electrical resistivity anomalies that are poorly
recovered using Z data alone; (3) improvement in the characterization of the bottom and
lateral boundaries of the anomalies with low electrical resistivity; and (4) superior
imaging of the horizontal continuity of structures with low electrical resistivity. These
advantages offer new opportunities for the MT method by making the results from an
MT profile in a 3-D environment more convincing, supporting the possibility of high-
resolution studies in 3-D areas without expending a large amount of economical and
computational resources, and also offering better resolution of targets with high
electrical resistivity.
Source
Geophysical Journal International, accepted 20th September, 2016. [PDF preprint]
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Alan G Jones / 20 September 2016 /
alan.jones.geophysics -at- gmail.com