Gravity Surveying Gravity Surveying 1. Introduction Gravity surveying involves the measurement of subsurface geology on the basis of variations in the Earth's gravitational field generated by differences of density between subsurface rock. The main control of rock density variation is its composition and porosity. Density increases with depth due to compaction and progressive cementation.
Porosity is one of the main controls of density variation in sedimentary rocks.
Whereas composition is the dominant control of density variation in metamorphic and igneous rocks. For example, the density of an igneous rock increases from acid to basic due to a decrease in silica content. When evaluating gravity data, a knowledge of the theory of gravity, and an appreciation of the aquisition and processing of gravity data should prove fruitful when interpretating subsequent geological anomalies. The power with which 2 masses will attract one another is proportional to the given mass and conversely proportional to the square of the distance. This is known as 'Newton's Law of Gravitation' as Newton framed it in 1686.