Gravity

Gravity data measures variations in the Earth’s gravimetric field caused by variations in density of the underlying rocks.  It provides valuable information on basement topography and the nature of the deeper parts of the crust and mantle beneath the basins.  Important intra-basin elements often have an associated gravity signature indicating that each element is related to a deep basement structure.  Standard Free-air and Bouguer gravity images will contain information from all these sources.  The major aims of image processing are to highlight the more subtle features from the various sources, separate anomalies from different source depths, and to accurately position anomalies (i.e. so that they sit over their source).

Example densities for various earth materials from the School of Earth Sciences University of Melbourne.In order to interpret the geological source of a gravity anomaly, the data must be calibrated.  Gravity images show density contrasts within the crust, but the source of the contrast is not unique.  As a regional tool it gives information both on the density of bodies within the crust and on differences in mantle depth and composition.  Satellite free-air gravity also has a major contribution from bathymetry.  Thus, the nature of each anomaly as crust or mantle must be distinguished.  By combining the onshore gravity data with the mapped geology of the same region, the sources of many anomalies can be inferred and extrapolated offshore and/or under sedimentary cover.  Others require geophysical modelling which must be constrained by a geological model.  Calibrated interpretation of gravity data is a powerful tool for developing an understanding of basin shape.