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Legacy product - no abstract available

Legacy product - no abstract available

The Australian National Gravity Database (ANGD) contains over 1.8 million gravity observations from over 2,000 surveys conducted in Australia over the last 80 years. Three processes are required to correct these observations for the effects of the surrounding topography: firstly a Bouguer correction (Bullard A), which approximates the topography as an infinite horizontal slab; secondly a correction to that horizontal slab for the curvature of the Earth (Bullard B); and thirdly a terrain correction (Bullard C), which accounts for the undulations in the surrounding topography. These three corrections together produce complete bouguer anomalies. Since February 2008, a spherical cap bouguer anomaly calculation has been applied to data extracted from the ANGD. This calculation applies the Bullard A and Bullard B corrections. Terrain corrections, Bullard C, have now been calculated for all terrestrial gravity observations in the ANGD allowing the calculation of complete bouguer anomalies. These terrain corrections were calculated using the Shuttle Radar Topography Mission 3 arc-second digital elevation data. The complete bouguer anomalies calculated for the ANGD provide users of the data with a more accurate representation of crustal density variations through the application of a more accurate Earth model to the gravity observations.

Deep-water Otway and Sorell basins developed during Gondwana break-up when Australia rifted away from Antarctica. The 2D and 3D gravity modelling in conjunction with seismic and geological interpretation has led us to an improved understanding of basement architecture of the study area. 2D gravity modelling particularly along selected seismic lines reveals a N-S crustal-scale lineament extending down to the Moho. A distinct density contrast of 0.16 t/m3 (3.05 t/m3 and 2.89 t/m3) across the structure points to a significant lithological difference at middle to lower crustal depths, interpreted here to reflect a change from dominantly basaltic to felsic lower crust. This structure is assumed to be inherited from a pre-existing basement structure and supports the hypothesis that the evolution of the Sorell Basin was probably basement controlled. The 2D models also help us to conclude the basaltic underplating in the lower-crustal region resulting from the breakup history, all long the margin. The computed 3D gravitational response of the basin-wide seismic interpretation correlates moderately well to the observed gravity trend, which implies (a) consistency between the seismic and gravity data of the inferred model. (b) Throws some light on basement topography, hence gives an idea of possible depo-centres. The depth to magnetic basement map derived independently from magnetic data has given a close proximity with that obtained from the 3D forward modelling, which essentially enhance reliability on the derived model to a good extent.

Legacy product - no abstract available

This Report lists stations of the Australian gravity base-station network. It gives values both on the old (Isogal65) and on the new (Isogal84) international gravity datums. Formulae are given for calculating gravity anomalies, and for converting between the two datums within Australia.

Encyclopedia entry describing different characteristics of raw gravity data, definitions of different anomalies, corrections to be applied, offshore, onshore data treatment, intricacies of Bouguer, terrain and indirect effects

This grid represents gravity anomalies of the Australian region. The grid combines accurate onshore gravity measurements, a sub-sample of the levelled offshore marine gravity traverses with satellite data used in areas where there is no marine data. The cell values represent simple Bouguer anomalies at a density of 2.67 tm-3 onshore and free-air anomalies offshore. The grid cell size is 0.5 minutes of arc, which is equivalent to about 800 metres. The smallest wavelength contained in the grid is 1600 m.