Electrical Conductivity Structure of the Australia Continent

Principal Investigator

F. E. M.(Ted) Lilley

Research School of Earth Sciences

A wide range of sets of electromagnetic induction data now exists for the Australian continent. These data show regions of the continent where the conductivity structure is approximately one-dimensional on a gross scale, relative to zones, called "conductivity anomalies", where induced electric currents flows preferentially. In this project, a thin-sheet model is considered to interpret these data. Progress is being made in the development of a numerical method which inverts such data automatically, to derive a thin-sheet model for Australia.

Co-Investigators

L. J. Wang

Research School of Earth Sciences

Projects

v63 - PC


What are the results to date and the future of the work?

A conductivity model for Australia has been obtained by inverting the data. In the inverted model, the known regional conductive anomalies, which were investigated by previous studies, are well imaged. New information from this conductivity model is (1) this model gives the position, extension and shape of the anomalies, so that the relation between the anomalies can be seen; (2). the model gives conductance values for the anomalies.

In future work, the inversion program will be applied to interpret the Queensland electromagnetic induction data. The conductivity model derived from Queensland will give a detailed picture of the Carpentaria anomaly in a three-dimension sense.

What computational techniques are used?

The inversion is achieved by minimising both misfit function and model roughness function. The misfit function is least squares misfit and model roughness is the first derivative roughness.

The model changes at each step of the inversion procedures represent a compromise between fitting the data and reducing the model roughness. The compromise is adjusted by a weight factor lambda. A conjugate gradient relaxation method is used to solve the final equation.

Publications

Wang, L.J., Lilley F.E.M and Chamalaun F.H, The large scale electric conductivity structure of Australia from magnetometer arrays., Exploration Geophysics, 28, 150-155. 1997.