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


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.


Geophysical Journal International, accepted 20th September, 2016. [PDF preprint]

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Alan G Jones / 20 September 2016 / alan.jones.geophysics -at-