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On the Effects of Finite Dipoles in 3-D Magnetotelluric Modeling
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 81st EAGE Conference and Exhibition 2019, Jun 2019, Volume 2019, p.1 - 5
Abstract
Electric fields are measured across dipoles of typically 50m to 200m at ground Magnetotelluric (MT) soundings. Modeling algorithms, however, normally use point electric field values at the surface of single cells to calculate MT transfer functions.
This is perfectly reasonable for the majority of cases, but there are situations with strong shallow variability of resistivity, where available detailed information might not be used optimally. We explore the consequences of this omission by quantifying the difference between point solutions and electric field integrations across dipoles in 3D forward calculations for selected cases.
The topic ties closely with galvanic distortion and inversion for related parameters, lateral magnetic field variations, and the benefit of providing shallower constraints for the imaging of deeper targets. As a side product, the analysis led us to focus on the fields output from the 3D modeling, and we illustrate electric current systems through the cases analyzed. We observe that in the presence of strong topography and outcropping inhomogeneities, finite dipole solutions can differ considerably from point solutions, while over a varying but continuous regolith cover the effect appears more contained.