Interpreting the Eromanga and Georgina Basins from magnetotelluric data

Abstract

This study uses broadband magnetotelluric (BBMT) and audio magnetotelluric (AMT) data to model the Eromanga and Georgina Basins in the Boulia region of western Queensland. Extensive data analysis to establish dimensionality, strike and the presence of galvanic distortion was conducted before inversion. The OCCAM 2D MT inversion code was used to produce conductivity sections for interpretation. The results of OCCAM inversions were compared the results of other inversion codes to ascertain the presence of any inconsistencies in the results. Several inversions were run for each profile to optimise inversion parameters with detailed inspection of data fit at each site to establish any systematic data misfits. Inversions were run on the full frequency of AMT data first as the resolution of the data was better. The broadband data was subset to frequencies above 0.4 Hz to focus the inversion on resolving the shallow features. A priori knowledge from the AMT inversions was very useful in interpreting the lower resolution BBMT data. Independent constraint in the form of drillhole and seismic data was used to aid interpretation of the inversions profiles. The BBMT inversions allowed the two-layer Georgina Basin signature evident in the south of the project area to be traced further north. They also delineated more complicated basin morphology in the west of the project area.