Geophysics is the study of the physical characteristics of surface and buried rocks, such as their magnetic properties, electrical conductivity, density and natural radioactivity.
The Geological Survey of NSW (GSNSW) conducts geophysical surveys and archives the data. Open file geophysical survey data from exploration companies are also archived for public access following title relinquishment.
GSNSW geophysicists use this data to provide information about geology at depth in the Earth's crust and help to define areas of mineral or energy resource potential. They use the information provided by field geologists to produce geophysical-geological map interpretations and to build 3D models of crustal geology. Geophysical data are also used with outcrop maps to validate geological cross-sections.
GSNSW conducts a range of geophysical surveys.
- Airborne magnetic and radioelement surveys acquire total magnetic intensity, radioelement and elevation data. They assist geological mapping and structural interpretation, particularly in areas covered by soil, alluvium, or younger rocks.
- Airborne electromagnetic (AEM) surveys measure the natural variations in the electrical resistivity of rocks, soil and water up to 500 m below the surface.
- Gravity surveys can be ground-based or airborne and map variations in rock density which help map covered geology and define areas of mineral and energy potential.
- Magnetotelluric (MT) surveys measure the electrical resistivity of the Earth at depths between 100 m down to 200 km depth, depending on the instruments being used.
- Seismic surveys use large trucks to generate pressure waves which penetrate into the Earth and are reflected from rock interfaces. The reflected waves are detected by an array of geophones and the data processed into seismic sections which image stratigraphy and faults. Seismic surveys can image from 100 m to 30 km depth depending on the equipment used.
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