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    Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Magnetic Anomaly Map of Australia, Seventh Edition, 2019 TMI Greyscale image is a greyscale image of the TMI grid of the Magnetic Anomaly Map of Australia, Seventh Edition, 2019. The 2019 Total magnetic Intensity (TMI) grid of Australia has a grid cell size of ~3 seconds of arc (approximately 80 m). This grid only includes airborne-derived TMI data for onshore and near-offshore continental areas. Since the sixth edition was released in 2015, data from 234 new surveys have been added to the database, acquired mainly by the State and Territory Geological Surveys. The new grid was derived from a re-levelling of the national magnetic grid database. The survey grids were levelled to each other, and to the Australia Wide Airborne Geophysical Survey (AWAGS), which serves as a baseline to constrain long wavelengths in the final grid. It is estimated that 33 500 000 line-kilometres of survey data were acquired to produce the 2019 grid data, about 2 000 000 line-kilometres more than for the previous edition. The grid used to produce this greyscale image has a cell size of 0.00083 degrees (approximately 80m). This greyscale image shows the magnetic response of subsurface features with contrasting magnetic susceptibilities. The image can also be used to locate structural features such as dykes.

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  • This report describes seismic refraction, magnetic, and resistivity surveys on the Upper Pieman Power development scheme of the Hydro-Electric Commission of Tasmania. The purpose of the surveys was to determine the depth to the bedrock, and the nature of the bedrock and overburden at five localities, viz: Spillway of the Hanging Rock dam site, Buttress Hill dam site, Tullibardine Saddle dam site ) Murchison No. 4 dam site, and Boco Saddle dam site

  • This Record describes a seismic refraction survey on the Delville Saddle dam site on the west coast of Tasmania, carried out at the request of the Hydro-Electric Commission of Tasmania. The overburden of decomposed basalt and unconsolidated sediments is up to 270 ft thick. The seismic wave velocity in the decomposed basalt is 3500 ft/sec or less; the velocity in the unconsolidated sediments is 5000 to 6000 ft/sec. Correlation between seismic velocities and porosity for the Savage Dolomites suggests that some of the dolomites are very porous, and hence are likely to be permeable.

  • The Irrigation and Water Supply Commission of Queensland requested the Bureau to test geophysical methods in the search for underground water in shallow basins, coastal plains, or river flats. Locations south of Bundaberg were selected as test areas. The application of the seismic refraction method and resistivity depth probing showed promising results.