2.5D AEM and Geology

“Summary

The McArthur basin/EMU fault study has a classic 2D fault feature and a buried conductor with an off-end effect with other2D/3D effects away from the EMU fault. The collected AEM data has demonstrable AIP effects. A forward model of the predicted response near the EMU fault represents a synthetic observed signal from the cross-section in agreement with the AEM data. 2.5D gets it right in significantly more situations than 1D methods by honouring the information in the observed data, as illustrated by this work.

We explain the fundamental differences between 1D and 2.5D. Importantly, Maxwell’s equations are used to constrain 2.5D whilst empirical methods are commonly used in 1D.

Thus a near zero average misfit using stitched 1D models can be achieved with families of 1D inversions, whilst incorrectly predicting the geology. Therefore a low misfit does not necessarily indicate a good solution for 1D. The 2.5D method is a least-squares best fit of the observations and so the quoted misfit for 2.5D is a very different measure than for 1D.

The study demonstrates that 2.5D yields a much more satisfactory geology section and a better reconciliation with information contained in the survey data.”